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As yet another olympish event, I have named myself the “indoor antenna research station,” without taking a vote. I learned this approach from a recent political figure who made up his own laws.
As yet another olympish event, I have named myself the “indoor antenna research station,” without taking a vote. I learned this approach from a recent political figure who made up his own laws.
I have dedicated my extra AMT3000 transmitter to the important project of experimenting with and documenting indoor antenna and grounding methods. This is more fully explained on a web page I have opened:
http://www.kdxradio.com/indoor_antennas.html
This is yet another in a series of great part 15 projects launched by part15.us in which its members become part of a committee of development engineers to further the part 15 movement.
We had the Big Talker Shortwave Transmitter project, the as yet incomplete Deep Voice Long Wave Transmitter Project, and at times we speak of a Part 15 Radio Network Project.
Not to be overlooked are the many independent projects such as Radio8Z’s High Efficiency Transmitter, MRAM 1500’s End-Fed Dipole for shortwave, RFB’s anticipated Carrier Current Manual, and many others.
This Forum, and my special web page, will slowly begin to gather everything we can discover about the art of indoor antennas and grounds.
Carl Blare
Total posts : 0Whereas most of us know that metal objects “receive” RF energy present in the air from many sources, it was interesting to note that, with the AMT3000 turned OFF, the test points (T1, T2) showed a voltage of 1.69 VDC. I presume this is energy being picked-up by the antenna system.
What this made me think about, was the idea of making a note of an antenna’s “idle” voltage measurements, when NOT being actively used for transmission.
Furthermore, this “idle” voltage needs to be tested with our OTHER transmitters turned OFF, then ON, to see whether they are contributing to this residual voltage.
If we find that voltages are being induced in nearby antennas by our own transmitters, it will open the discussion on “What should we do about it.”
RFB
Total posts : 0You guessed right. Those antennas are picking up other EM fields and since that antenna is connected to a tuned network in front of it, yes your test points before the network circuit is going to reflect some voltage the antenna is picking up, plus being tuned by the matching network. It don’t matter if its picking up an on frequency signal or way off in la la land elsewhere, it’s still going to do what it’s doing because of one thing I have mentioned about before….
..all those close proximity transmitting wires in the house.
There are several solutions to this little problem. All the more easier to deal with since this is micropower. Now imagine trying to null out that mess from a 50kw AM or 100kw FM. It does happen, and there are some very fancy, very expensive pieces of equipment put on the feedlines to reduce that residual residue.
Band-pass filters, direct DC shunt relay to ground upon TX shutdown, disconnect the wire antenna when done, re-locate the transmitters and antennas away from each other.
I think you picked a good subject to begin the new Indoor Antenna Research idea, a problem that most are not aware of until they discover it by accident like you did.
RFB
Carl Blare
Total posts : 0It is always easier to “think behind” (hind-sight is 20/20).
But I now try to think ahead, imaging what it would be like to feed the questionable antenna into the input of the on-order spectrum monitor.
I will pre-guess that the spectrum will show all the activity taking place within 50-miles, but it will also show which personal transmitters are showing up on the antenna, how strong they are, and they should disappear when each transmitter is turned off.
Testing every piece of metal in the house with the spectrum analyzer will be more fun than broadcasting. I may discontinue our program schedule and watch that spectrum all day.
RFB
Total posts : 0Well I can guarantee you will be more entertained and informed by that spec-an than from the skinny (fat for crt types) glow box in the corner or hanging on the wall. At least the spec-an won’t lie to you.
RFB
radio8z
Total posts : 0Years ago I was building a RF white noise generator for a project and all went well except for the testing which showed an almost sine wave “oscillation” when viewed with a scope. I spent hours trying to figure out why the circuit was oscillating and finally I checked the frequency…it was 700 kHz. Then I realized that since I lived 7 miles from the WLW tower (50 kW at 700 kHz) that the oscillation wasn’t real.
Even now, there are times when I have to shut down the AM transmitter to do bench tests. They may be Part 15 signals but up close they are strong.
Neil
MICRO1700
Total posts : 0I can’t remember when or how or
why – and I eventually solved the
problem. But it did happen.When we got a phone call, I had
to turn off the AM transmitter.
Then I showed everybody in the
house how to do it.I never thought that small amount
of energy from a Part 15 AM rig
could do that.Bruce, DRS2
Carl Blare
Total posts : 0The near fields produced by part 15 AM transmitters are unexpectedly strong. In the kitchen the receiver overloads from the AMT5000 / 1680 AM antenna, 10-feet away, which is why I run 1550 AM from 3-rooms away, so the kitchen radio gets a clear signal.
Now that I have the cordless phone I also finally have a Caller ID Screen, which I’ve been paying for, but previously couldn’t see.
Every so often I get a hang-up call on the answering machine in which KDX audio plays loud and clear on the answering machine until it hangs up. This was very confusing at first, because I thought someone was calling and deliberately playing back my station on the telephone. That would be very weird. But Caller ID shows “Card Services” and “Charity Clothing”, two telemarketers. I still don’t know how my station is getting on the answering machine. I never get KDX on the telephone when making calls.
RFB
Total posts : 0““The near fields produced by part 15 AM transmitters are unexpectedly strong. In the kitchen the receiver overloads from the AMT5000 / 1680 AM antenna, 10-feet away, which is why I run 1550 AM from 3-rooms away, so the kitchen radio gets a clear signal.”
Remember when you first got the LPB TX 2-20 and took it apart to FTC it? And do you remember when you had the exciter on the bench, sitting right underneath your..what is it you guys call that 13 Mhz thing…loud mouth, big mouth something talker…:p
Anyway you fired up that exciter, outside of it’s protective metal casing and what was it you experienced?
Audio from that 13 Mhz signal inductively coupling into the exciter electronics and embedding that induced signal (modulated) onto the exciter’s dead air carrier.
Scaled down, it was like us weebees here on this rotating ball floating in the either getting a massive CME shower. Fortunately you shut it down and moved things before proceeding and got it going!
Yep, this Indoor Antenna Research thing will be great! Lot’s of discoveries and surprises to unfold!
RFB
MICRO1700
Total posts : 0A couple of years ago, I was
working on a tuning unit for
my AMT-3000.I had a battery powered CD player
feeding the SS-Tran. When I peaked
the system, the CD player stopped.
It couldn’t function within the
strong RF field. (This system became
the tuning system I used a few years
ago, which worked well.)RFB: I have been working on my version
of the 13 MHz Big Talker. As I assemble
it, I have learned one thing: I can’t
build SMALL. What I have will be done
soon, and if it works, it will go into
a box. So far, the 3 stages are TOO big
for the box. Maybe I SHOULD name it
BIG MOUTH!Bruce, DRS2
Carl Blare
Total posts : 0Quick catching up of the current indoor activity….
Built a loading coil on a triangular form instead of a round form,
Tuned it up at 1550 AM on AMT3000,
the only grounding is the jumpers that put RF ground down through the power transformer,
today took the first drive into the eastern uphill field and heard a strong signal for 2.5 blocks, about 1-block farther than the AMT300 reached using the internal tiny inductors.
Whoa! Wait until a better ground goes in!
And it’s all “functionally compliant!”
RFB
Total posts : 0Sounds great! Functionally compliant? What exactly is that anyway?
So many different angles to one simple thing of compliance. Amazing! 😉
RFB
Carl Blare
Total posts : 0Thought about that question, RFB, and I think it would be possible to have a “non-functionally compliant” part 15 station. Sure. Makes perfect sense. Also, there could be a functionally non-compliant station. Most of all, COMPLY! WE WARN YOU.
But on to indoor antenna business.
As you know, one way of studying the results of particular indoor antenna experiments will be to view the Spectrum Analyzer (SA) to see how it compares to other antenna experiments, and how changes to the antenna affect the spectrum analysis.
Of course the SA will need its own antenna at the input, and as we’ve discussed, we will roll-our-own for starters. Later on we will invest in the professional loop-antenna you mentioned, of the type used by the FCC (pronounced “fissss”).
For simple home-spun use, would a plain vertical wire be sufficient for indoor testing?
RFB
Total posts : 0“For simple home-spun use, would a plain vertical wire be sufficient for indoor testing?”
Yes. At least for your SW and VHF signals. For HF and MW/LW your going to need a loop antenna if you want as close as possible to accurate measurements. And close is better than no where near the ball park.
Although I have an LP-3 loop, I built one using typical loop antenna construction techniques. It’s square, about 3 feet each side and has about 180 windings on the coil. A 350pf variable is across the leads for fine tuning and a home brew 50 ohm balun feeds the coax to the spec an.
Again this is not nth decimal accuracy, but were not striving for nth decimal accuracy. Your striving for a way to be able to take some kind of measurement of your stations by going beyond the use of a simple radio with an S meter or cruising around in the car with the radio on determining where noise begins and why the cop behind you wants you to pull over for running the stop light because you were fiddling with the tuning button on the radio. (hypothetical scenario there!)
When you get the actual measuring done for documentation, you can calibrate and note your readings versus readings on the other test equipment. Once that is done, you will have a way to make sure those signals are at or below those readings taken by the more accurate equipment.
Now I will pitch this question out there for anyone to answer.
Do the actions being taken by Carl and going so far as purchasing a spectrum analyzer, that he is doing everything possible and within his ability to make sure his operations are …”functionally compliant”??
I think so.
RFB
Carl Blare
Total posts : 0I don’t think levity, jocularity, kidding around and silly nonsense make the right impression with severe literalist part 15 by-the-book fundamentalists, but that’s all this is, when I say….
I want to be able to accurately measure the exact milliWattage to the hair’s perfection, and then give it one extra boost.
We are not trying to prove to our patriarch that we honestly obey the curfew and never imbibe on Sunday.
Even though I enjoy the part 15 pastime, the teeny-tiny measuring of magnifying-glass nearly undetectable quantum particles is too silly to remain a stoicly reverent discipline.
It was even meant to be a joke when the FCC set it up. It had to have been.
Rich
Total posts : 0… if that is of any concern.
Mr Blare wrote “I want to be able to accurately measure the exact milliWattage to the hair’s perfection, and then give it one extra boost.
Just to point out that an accurate measure of the input or output power of a “Part 15 AM” transmitter using an intentional radiator is not proof that such a system is compliant with Part 15.
The paper linked below shows why (note the difference in range to the same field intensity for the two systems while using equal tx power, based on their antenna configurations — without an “extra boost” in that tx power).
http://i62.photobucket.com/albums/h85/rfry-100/AM_System_Comparison.gif
RFB
Total posts : 0“Just to point out that an accurate measure of the input or output power of a “Part 15 AM” transmitter using an intentional radiator is not proof that such a system is compliant with Part 15.”
A very valid point right there, and one that should ring a bell in everyone’s memory…ie KENC.
We have seen even a certified transmitter can be found to be out of compliance by simply where it is mounted and what it is using to connect itself to ground (dirt).
For 221 it’s the same, except a 221 system is not trying to establish a far field signal to reach a 1/2 mile away from the wiring. But like 219 there are specifications that must be met.
Best way to do this is to have on hand something to be able to measure with. A good general tool is a radio with several bands and an S meter. However that tool is very limited in what it can tell you.
Either way, a radio with an S meter or an investment into a piece of test gear that will serve more purposes than just checking Part 15 signals, effort is being made to have the tools on hand for checking compliance and to be in compliance.
I can’t think of any other better way for a Part 15 operator to make sure they are in compliance.
Only other way is to just shut it all off. Would that then be considered “functionally compliant”?
RFB
Rich
Total posts : 0I can’t think of any other better way for a Part 15 operator to make sure they are in compliance. Only other way is to just shut it all off.
Another way would be to install the transmitter plus its attached ~3-m vertical whip so that the top of the whip is 3 meters above the earth, with the transmitter r-f ground terminal connecting to something buried in the earth via a conductor only a few inches in length.
Then, if the transmitter input power is 100 mW or less (unmodulated), the system will comply with 15.219, and field intensity measuring equipment will not be needed.
RFB
Total posts : 0“Another way would be to install the transmitter plus its attached ~3-m vertical whip so that the top of the whip is 3 meters above the earth, with the transmitter r-f ground terminal connecting to something buried in the earth via a conductor only a few inches in length.”
Based on public available data in how testing for compliance is done with Part 15 devices (not just AM or FM transmitters) is the DUT is placed upon a table that is 1 meter in height sitting on a ground plane system. Since the DUT was certified at this height and given an FCC certification number, there should not be any out of compliance issue if someone has a Rangemaster or Procaster or TH/iAM ATU mounted in the same manner.
Of course that could be said to only apply to certified units and not kits or home built systems.
However there are no rules stating that a Part 15 AM intentional radiator, certified or not, MUST be mounted at ground level (dirt).
However mounting it close to the ground improves the return pathway with less ground path resistance through a conductor longer than a few inches. The less ground resistance to the dirt the better, and the better conductivity footprint in the dirt is even all the more better, as well as eliminating the “ground lead” nonsense and eliminating any chance of a long ground path radiating.
RFB
Carl Blare
Total posts : 0My ever so carefully measured system would be exactly as you describe, with a 3-meter vertical and buried earth grounding.
First you said that would be no assurance of compliance,
then you assured me it would comply (100mW at the final input).Time out.
Are we repeating ourselves, over and over and over and over and over and over?
Time for the boost.
Rich
Total posts : 0My ever so carefully measured system would be exactly as you describe, with a 3-meter vertical and buried earth grounding. First you said that would be no assurance of compliance, then you assured me it would comply (100mW at the final input).
What I wrote was that using a transmitter with 100 mW input power to the final r-f amplifier did not assure compliance with Part 15.219, because such compliance also requires using a compliant antenna system.
Buried earth grounding doesn’t necessarily mean that such an r-f ground is not connected to an elevated transmitter by one or more long, radiating “ground” conductors.
Some claim that the top of such a long conducting path connected to a buried r-f ground also is r-f ground, but it is not. That long conducting path radiates, and this issue has been the source of several NOUOs issued by the FCC.
The reasons I post this information more than some people want to see it are (1) that the point never appears to be accepted, and (2) it might help someone who wants to avoid an FCC action.
Carl Blare
Total posts : 0This forum is concerned with indoor antennas, and unless we live in an old church or auditorium, we will not have elevated antennas with long ground-lead attachments.
But I know that long ground leads is the inevitable outcome of many conversations in the past and many to come in the future, so I strongly suggest a dedicated forum be opened on “Long Ground Leads”, where the subject could exist without need of non sequitur.
Back to the subject at hand, the Spectrum Analyzer has just arrived by postal delivery and I guess I’ll spend the day reading its literature and planning where to install.
Then, maybe tonight, I’ll round-up available plans and instructions for building a MW loop, and will do a triangular design, since they can be anywhere from round to square.
Mr. rich, do you have any input re: loops?
RFB
Total posts : 0Although this is about indoor antennas, grounding topics are important here as well.
Reason? An indoor antenna’s ground can also radiate if it is long enough to overtake the short wire’s length. The TX will cause the longer conductor to radiate rather than the intended radiator, which is the wire, or custom built antenna. They all need something for a return path for the RF.
Usually this ends up being either the ground via the audio cables, power cables or the enclosure of the TX connected to some form of ground system via copper strap or wire. But the same result will occur, long grounds will end up radiating.
Perhaps what might help in this situation would be the approach taken by neutral coupling in CC, installing an isolated Earth ground and use that for your return path for your indoor antenna, or attach to a cold water pipe.
Anything but attaching to the home’s electrical wiring ground or utility ground. Turn the whole house’s wiring into a radiator.
This indoor antenna research plan is fantastic and I think Carl deserves a huge salute and well wishes for creating a new area of study in Part 15.
RFB
Rich
Total posts : 0RE: .Perhaps what might help in this situation would be the approach taken by neutral coupling in CC, installing an isolated Earth ground and use that for your return path for your indoor antenna, or attach to a cold water pipe.
Just have to remember that the only part of a cold water pipe that won’t radiate significant r-f energy is the part of it that is actually in contact with (buried in) the earth.
Once the copper/galvanized pipe from the water main enters the basement wall to connect with whatever cold water outlets exist in that structure, those indoor conductors will radiate — if the “ground lead” of a Part 15 AM transmitter is connected to them anywhere.
And as stated by RFB, the same will result from connecting the transmitter ground lead to the a-c neutral, because that path does not meet the earth until it reaches the grounding rod used by the utility company, near the service entrance outside the building.
Carl Blare
Total posts : 0Thank you for the input on grounding.
Setting standards for my anticipated series of indoor antenna tests I state the following:
– I do not intend connecting transmitter RF ground to AC neutral;
– I do not intend connecting transmitter RF ground to water pipes.
Therefore those two subjects are removed from further discussion in this Indoor Antenna Forum.
CAVEAT: If a contributor believes there is a reason I should reverse either of those stances, bring it in.
Rich
Total posts : 0I do not intend connecting transmitter ground to AC neutral; I do not intend connecting transmitter ground to water pipes.
You might want to consider whether or not to put in your own, dedicated ground rod too, because the conducting path from the transmitter r-f ground terminal to reach that ground rod also will radiate.
Of course one doesn’t really need an r-f ground for an indoor antenna for lightning protection, but the signal coverage of that system will be less than otherwise.
And I guess that what people intend to do isn’t always what they actually do 🙂
Carl Blare
Total posts : 0And I guess that what people intend to do isn’t always what they actually do 🙂
–rich — quote/unquoteThat seems a little snide. Especially with the smile tag.
RFB
Total posts : 0Regardless, a proper working system requires some kind of complete circuit path to properly function. This means for our subject matter, an RF ground.
True one really does not need this if only attempting to send a signal to the other room. However having good ground can eliminate more problems such as inductive coupling into audio gear and audio lines, or causing unexpected interference to your own stuff in your own home.
There is very little that will radiate from a cold water pipe once connected to it, especially if you connect as close as possible to where the mains pipe comes up into the home. And keep the ground wire from the TX to that water pipe as short as possible, again to reduce the resistance along that return path for the RF for better ground, and to prevent unintended radiation.
Never thought I would see a day when ground was such a debated subject. Well I recall a time when it wasn’t. Why so now?
Anyway, on with the research!!
RFB
Carl Blare
Total posts : 0The legal questions about part 15 ground have become controversial, but the actual importance of RF ground for good performance is vital knowledge that can be under-appreciated.
I am the poster child for being clueless about RF ground, having for years thought that the antenna alone was the key to success.
The discussions on this website have slowly penetrated my “knows-it-allness” and made me finally wake up to how important RF ground is.
This indoor antenna project will very much address RF ground, and from a separate point of view, the legalities of various ground schemes.
WOOPS! I just responded to a comment made by RFB on the tail end of page 1, and here we are are page 3.
As far as the hexaganol antenna is concerned, where is the feed point?
RFB
Total posts : 0“As far as the hexaganol antenna is concerned, where is the feed point?”
It’s nothing more than a loop with the shape of the hexagon. The feed point would be at the two ends of that loop.
Take it further and construct a second hexagon loop inside the first for varying it’s tuning, like a variable inductor, which basically that’s what it becomes.
And it might be easier to design something “wife friendly” since it is more than just a circle of wire surrounding the family pictures on the wall.
Was just a thought that perhaps you might want to consider in the indoor antenna projects.
RFB
Carl Blare
Total posts : 0RFB, while thinking about how the hexagon would look on a wall, I suddenly thought of picture frames. Everyone has picture frames.
Art museum exhibits sometimes have pictures over ten-feet tall, or for that matter it could be a framed mirror.
But imagine a custom made 8X10 stainless steel frame with a continuity break in the bottom containing non-conductive construction material, the frame acting as a “great loop”.
Or really, a wooden frame could be lined with wire to make it more of an at home project.
Another dimension I’m going to toy with are indoor loading coils. The biggest problem with them will be making them “fit in” to the decor.
RFB
Total posts : 0There are those large combination picture frames where you can put varying sizes of pictures. Some of these are your basic square shape or rectangle shape, even simple circles or oval shapes.
It’s just a matter of using the imagination with what exists and putting the two together. Something is bound to turn on that great idea lamp above the head!
How about drapes that also act as an antenna, or the drape rails themselves.
RFB
mram1500
Total posts : 0Don’t forget the lamp shades! They have wire loops also.
In fact, they’re almost like your caged monopole.
Carl Blare
Total posts : 0A ten-foot lamp shade would be sort of interesting.
As for drapes, don’t some shortwave stations have “antenna curtains”?
Maybe I’m imagining that.
mram1500
Total posts : 0I guess I was thinking of the lamp shade for your FM operation.
Carl Blare
Total posts : 0Oh, I see, you mean a five-foot lamp shade.
Ken Norris
Total posts : 0I haven’t had time to read thru this whole topic, but I like the cage monopole idea. What if you just leave the ground connected thru the PS and/or audio, then attach the TX ground to a 1.5m cage and the antenna side to another with a tuneable loading coil and TX in the middle?
Build the whole thing on a 6″ PVC form with 6 wires lengthwise for each cage section, mount horizontally out of site in an attic.
Carl Blare
Total posts : 0Hi Ken Norris, I LOVED your Walkie Talkie this weekend from Jan Juan County Fair. Do you know it’s the main feature on Low Power Hour No. 43?
The cage-monopole we are talking about WAS on the Wholehouse 2.0 FM transmitter, and when I first built it, it seemed very much (subjectively) that the antenna stopped all multi-pathing as I walked in the room. But that only held true until I moved the tower to a different location.
So, fast forward to some interesting discoveries.
Since I now have a Spectrum Analyzer, I watched 107.1mHz as I removed each leg of the monopole, one by one. The peak level did not change.
The most surprising thing was that when I removed the entire antenna, cut to 1/2 wave, THE PEAK ON THE SA REMAINED ABOUT THE SAME! In other words, the antenna didn’t seem to be doing much at all.
So I learned how to open the Wholehouse for a look inside, and checked the antenna wire for connection and continuity. It was fine.
Aside from all that, your description of a dipoled cage-monopole is excellent.
Carl Blare
Total posts : 0My indoor antenna work will be in the preparation stage for awhile, as I slowly inch toward having everything in place to begin publishing actual findings on the link page I’ve created (linked earlier). But there will be piecemeal experiments from time to time.
For example, I think it was Radio8Z who talked about loading coils used in certain indoor installations, so I am right now spending time fiddling with ideas for a special breed of loading coils designed for the indoor setting.
I happened to have built an indoor loading coil in a triangular configuration rather than the standard circular design. I have an interesting result to mention now.
Using an AMT3000 Transmitter feeding my mid-efficiency Wintenna, I have observed a +7dBm improvement on the Spectrum Analyzer when using the triangular coil, as compared to the internal inductors within the AMT3000.
But it was necessary to keep S7 OFF, whereas the modification for an outdoor loaded coil antenna would require S7 to be ON. There are good reasons for this, as the outdoor antenna would be away from walls on other obstructions, whereas the Wintenna is literally built into the wall, which radically changes its capacitance.
There may possibly be a few more dBm to squeeze out of this setup, by finding a better tap-point on the coil.
RFB
Total posts : 0Where was the SA in relation to the triangular coil feeding the “Wintenna” and orientation of the triangle coil?
I’m wondering if your coil is reacting more like a radiating inductor than a loading coil for the Wintenna.
What’s the size relationship of the coil vs Wintenna and it’s connecting scheme/distance?
RFB
Carl Blare
Total posts : 0I added another tap giving the coil 4-more-turns of length, and added 1-dBm to the gain shown on the SA.
The Signal Analyzer is still on my desk, but I moved its 13″ telescopic antenna to a spot 7-feet away from the Wintenna (previously 3-feet).
The AMT3000 is on the floor below the window, the triangular coil is laid horizontally rather than vertically, based on a mention that this can improve transmitting antennas (ARRL Handbook).
By the way RFB, the loading problems we talked about in e-mail were solved by changing a jumper in the AMT3000 (S7).
There is another significant addition to the mix, a baseboard dipole running 24-feet in both directions, total of 48-feet, tapped in the center and connected to transmitter ground. This creates an indoor ground plane. I have yet to analyze how that is affecting or effecting the overall result. In addition to doing this, I need to figure out how to use Team Speak.
Pity about Pussy Riot.
Carl Blare
Total posts : 0I don’t really know what that means, but they say it in television production. Strange, because I worked in television and ran a video service. We never said, “It’s a wrap”, but I think it means, “That shot is fine let’s use it.”
Now I need to circle back to the subject of indoor antennas, and we have achieved our first success ready for publication. The key to the final solution to this particular antenna experiment was found in this publication, NOT part of the AMT3000 Manual, but linked at sstran.com
http://www.sstran.com/pages/COMMON/sstran_buildant.html
I’ll start at the end of this story, then fill in detail until there is a beginning.
When I thought I had “succeeded”, I was hearing modulation distortion, and that’s never a good sign. But the sub-conscious mind remembered something I had read about adjusting the output of the AMT3000 using a quality voltmeter.
First I read the Manual, but didn’t find what I was looking for. So I dug into the file folder and retrieved my copy of the Construction Instructions for Building a Base Loaded Vertical, back on Page 10…
Item 9. If the voltage reading at the tuning peak is greater than 13 volts DC, increase the trimmer, C5, capacitance by rotating the trimmer clockwise until the voltage drops to 13 volts DC. If the voltage is not reduced to 13 volts DC, your RF signal output may be distorted resulting in distortion of the received signal. When the meter reads 13 volts DC, the antenna is perfectly matched to the transmitter.
Before making this final adjustment I was seeing a meter reading of 15 volts DC, higher than I’ve ever seen before using the AMT3000.
Since tuning to 13 volts DC there is no more audio distortion.
The artificial ground method described by Radio8Z, rich, and anticipated by myself, works wonderfully and is dramatically better than expected.
It is a 48-foot length of wire strung horizontally along the baseboard, center-tapped, with the RF ground feeding the center of the wire, putting 24-feet of wire extending to the left and right of the transmitter. The choice of 48-feet is arbitrary in any electrical sense, and is based on the length of the available baseboard space.
With the artificial ground removed the Signal Analyzer shows a 30 dBm drop in signal level.
The loading coil is wound on a triangular form, which previous discussion predicted would work the same as a circular form, is laid horizontally, wound with insulated hookup wire for a distance of 7 3/4-inches (late some night I’ll count the number of turns).
A vertical antenna wire rises from the coil and attached to the bottom of the metal window frame. Out on the porch an additional length of wire is connected at the top of the window frame and extends straight up to the porch ceiling. The sum total vertical height is about 10-feet.
A permanent documenting of this experiment will be posted on the project page, linked at the beginning of this thread.
Carl Blare
Total posts : 0According to all measurements at my disposal, the antenna output from the AMT3000 transmitter at 1550kHz with loading coil and grounding dipole is better than previous, the actual performance in the field is poor, compared to previous results.
My guess is that the ultra-dry ground is playing a role, given our long drought condition.
As a comparison, our carrier current system picked up dramatically when I wet the ground at the ground rod, and fell off completely a few weeks later when the ground dried out.
The Mars conversion going on here on earth is changing radio behavior.
Carl Blare
Total posts : 0While testing the AMT3000/triangular loading coil/Wintenna, I spotted some out-of-band peaks showing up in the LW band between 204 and 217kHz, about 30dB below the main carrier at 1550kHz.
These “spikes” followed the bandwidth, appearing every time a strong sibilance or high-frequency sound modulated the carrier.
RFB advised that this might be SW (standing wave), energy being reflected back to the transmitter and causing the out-of-band action.
Knowing from previous work with the AMT5000 on the other Wintenna, the capacitance of these antennas is much higher than an antenna located away from obstructions, and that transmitter was brought to a proper load be feeding the RF through a 20pF capacitor between the loading coil and antenna.
The AMT3000 being a different transmitter, with a different loading coil, I found that a .01uF capacitor between loading coil and Wintenna completely prevents the LW spikes without sacrificing any signal strength.
Carl Blare
Total posts : 0The baseboard is the wooden strip that intersects every wall in a house with the floor.
For indoor antenna installations a HAM operator once suggested stringing wire along the baseboard to create an artificial ground.
I think it was Radio8Z, but it could have been MRAM, who talked about a two-element radial built by center-tapping a long baseboard wire and attaching the transmitter ground.
I have installed such a baseboard 2-element radial and also call it a shunted dipole, since it is electrically joined at the center point.
As I described already, this greatly improved the loading of my coil/antenna and gave a higher peak reading on the Signal Analyzer.
I want to seek a few opinions on further describing such a ground system.
One issue I wonder about is the fact that a baseboard is not one long straight distance, but makes left turns and right turns to shape itself to the rooms and doors.
If a bi-polar ground radial makes so many sharp turns to follow the baseboard, what does that do to its RF performance?
If the transmitter ground were dropped down into the basement a more elaborate system of ground radials could be installed on the basement overhead, but it would be ultimately shaped by the basement space available.
In some cases a few radials could be projected outdoors and continue under the earth.
RFB
Total posts : 0Interesting. If it were me in such a situation, ie apartment or other condition where no access to Earth ground were around, and if possible, lay down steel or copper mesh and put throw rugs over that meshing which would be your ground plane.
I would think that with just single wires ran along the baseboards on the floor, the curves, turns etc would alter that ground’s effectiveness since those curves and turns would change the layout pattern of your ground system. Instead of nice straight runs of wire, they go zig zag back and forth hugging the baseboard along the floor.
Hopefully no one trips on one!
RFB
Carl Blare
Total posts : 0Appreciated your remarks about the baseboard ground plane.
I thought the turns and corners of the baseboard layout might pose a problem.
The copper mesh idea would work for some, but would probably be an off-center ground plane, because the antenna cannot be centered in the room… it’ll have to be along a wall.
I won’t do the mesh with throw rug because I hate rugs.
People trip on throw rugs everyday. Some of them hit their head on the coffee table and the rest of the family inherits their radio equipment.
By the way, and I hope you’ll get back to me on this, I think that water pipe grounds and electric service grounds introduce a lot of noise into the antenna path, picked up from all the junk that’s attached through the neutral and ground leads from all over.
Am I right about that?
RFB
Total posts : 0“I think that water pipe grounds and electric service grounds introduce a lot of noise into the antenna path, picked up from all the junk that’s attached through the neutral and ground leads from all over. Am I right about that?”
Yep. Considering the fact that ground is the place where noise and junk gets dumped by design in many devices used daily everywhere.
As more devices from household stuff to industrial get tied together via power or control communication, wired or wireless, all of it eventually has to take a dump somewhere!
Best place to put the stink is in the ground! 😀
Isolating certain segments of the EM spectrum where the junk is a problem can be filtered out, like for a receiver equipped with tight IF bandwidth notch filtering etc. Simpler examples are a loop antenna rotated to maximize signal vs the noise.
RFB
MICRO1700
Total posts : 0I may have to do an indoor Part 15 AM
system, eventually. This is of great
interest to me.Specking of RF noise – I’ve got a doozy
of a problem right now. Last night
I was getting “spark gap” noise from the
AM BCB up through 30 MHz. It would run
for about 20 seconds, then it would stop
for about 80 seconds, and repeat.It rained a little bit this morning, and the
noise stopped. I have reason to believe it’s
the power lines around here somewhere on the
street.Tonight, it’s back. I haven’t measured the
time intervals yet. This has been an intermittent
problem for years, but this time it’s really
pretty bad.Oh well. It’s time to catch up on those
Low Power Hours. I’ve been listening to the
meetings. You guys are doing a great job.I guess I’ll do that now.
Best Wishes,
Bruce, GNATs, SLUGs, etc.
RFB
Total posts : 0Anyone remember where that line comes from, what famous robot TV series back in the day?
Sounds like somewhere on the grid is a bad connection buckle along the HV high tension lines or static buildup on them discharging through the spark gaps.
Electricity is a neat phenomena!
RFB
RFB
Total posts : 0“Some claim that the top of such a long conducting path connected to a buried r-f ground also is r-f ground, but it is not. That long conducting path radiates, and this issue has been the source of several NOUOs issued by the FCC.”
This was never an issue prior to 2005. Then suddenly it was. I wonder why?
“Buried earth grounding doesn’t necessarily mean that such an r-f ground is not connected to an elevated transmitter by one or more long, radiating “ground” conductors.”
True it does not mean anything really. However you cannot just assume that every installation has a transmitter mounted up on a pole using that pole as it’s ground path.
Not everyone is a bad apple! 🙂
RFB
Carl Blare
Total posts : 0Mr. RFB made a good plea to keep grounding part of the indoor antenna discussion, although the conversation becomes very murky when considering such common practices as grounding to a water pipe.
If a water pipe happens to be vertical, say from a kitchen downward, where do we stand on compliance?
I tend to agree with Mr. RFB that a dedicated ground rod is much preferred over attaching to the home’s electrical ground. But with a dedicated ground rod, there’s the question of the lead in wire.
Usually the surface of the earth is above the basement floor level, therefore is the basement “under ground?”
I have the Spectrum Analyzer set on the floor, wondering where to put it. Right now there is no place anywhere of the size and location suitable for this large appliance.
In my head I asked, “What can be put off until tomorrow?”
The answer I replied is, “All of it.”
The next question became, “Since everything is put off until tomorrow, what will I do today?”
The reply, “I don’t know.”
Carl Blare
Total posts : 0I understand the lesson you have put forth. My exact “to the milliWatt measurements”, in themselves, are no assurance that my system actually complies with FCC book.
Therefore, my extra “boost” won’t matter, one way or the other.
ArtisanRadio
Total posts : 0I posted this before and I may even post it again.
‘THE RULES” are not black and white. There is interpretation involved, and while it’s interesting to see various people’s interpretations of said rules, the ultimate authority is the FCC. No matter how technically adept those people view themselves to be.
A few years ago, it was considered compliant to have a transmitter high up in the air grounded to a metal structure. Now, it is not. Did the rules change? No, the FCC interpretations changed.
So my suggestion for anyone starting up a Part 15 transmitter, new or experienced, is to read “THE RULES”, read threads such as this carefully, and then make informed interpretations of your own. After all, you have to live with them if the FCC comes calling.
And I suspect that intent plays a bigger factor than what some are willing to admit. But then, some think that everyone here goes out of their way to violate those rules.
Carl Blare
Total posts : 0Agitations and diversions aside, I will continue undaunted on the path of indoor antenna research.
I will not respond to phantasms about “rule violations” when that is totally off topic and I will not be prodded into mounting a defense against allusions.
If we have complex issues like narcissistic wound driven by guilt combined with remorse over not having become a recognized law enforcement hero for clamping down on ground lead violators, that should all be moved to a psychology discussion site.
Meanwhile, here in the wake of disruption, a Spectrum Analyzer is staring at me. I have no place to put it. Shall I change the subject yet again to that of “furniture for test gear?”
Sometimes confusion causes the brain to output unrelated products, like a bold scheme how someone could legally earn money building part 15 transmitter kits. It’s a lesson from the alternative-health-care field, where a legally paid massage therapist may provide “side services” at no additional cost. What I’m saying is, it would be legal to charge $300 for a nicely built transmitter cabinet, which contains, at no additional charge, a fully built part 15 transmitter.
Maybe the new network should use that for fund raising.
RFB
Total posts : 0Getting back on track so we don’t loose our place here, have you thought of any antenna designs so that they are more eye relaxing in a home setting?
Example, standing lamps and lamp shades for top hats. Ceiling fan loop antennas, swamp cooler coils and maybe a c-pol patio table? 😉
Actually kidding aside, researching and developing indoor antennas that appear like a standing lamp with an actual working light, loop antennas above a ceiling fan assembly or other would be great!
RFB
Carl Blare
Total posts : 0Good, RFB, perfect! Floor lamp.
I go through floor lamp listings at shopping sites and watch for “antenna friendly” designs, or possible ways of converting generic floor lamps with a design that any wife would approve of…. that’s the tricky part.
I almost have a space ready for the Spectrum Analyzer (SA). Clearing the space on my over-sized executive desk is taking all evening, because it has ten years of accumulation, at the very bottom of which are the N-scale train parts I never did anything with. I’m off-loading it all into a giant cardboard carton where it will be found by future generations.
Then the SA will be my companion there at the desk, so I can watch that spectrum for SETI (Sightings of Extra Terrestrial Intelligence).
What would they do if we set up a million Watter up on Mars, aimed toward earth?
RFB
Total posts : 0“What would they do if we set up a million Watter up on Mars, aimed toward earth?”
Unfortunately, since NASA has established a line of communicating satellites and surface rovers with on-board communications systems, and although they cannot claim any authority on any part of Mars, the FCC will step in and say “nope” because you could cause interference to that established line of communication between NASA and its remote probes.
However it would be interesting to see how well RF will propagate on that planet’s surface. It’s nothing more than a ball of mud ice layers (conductive/excellent ground) and thin atmosphere and very very little other man made electric/electronic/RF noise.
How about we actually set foot on the planet first and then set up our megawatt monstrosity and turn Mars into our own version of Death Star. :p
RFB
Carl Blare
Total posts : 0It’s a morning, probably Wednesday, here on earth, center of North America, an indoor antenna research station.
Upon advice from member RFB, a spectrum analyzer (SA)was obtained, arriving yesterday from all the way in China, and many hours were spent in simply making a location to install the device.
The hours from 11 PM to 1 AM were spent learning how to view the highly interesting picture of the RF spectrum obtainable on the device.
The first big find was the FM spectrum, 88 to 108mHz, with its many peaks and valleys; beaming signals and the slim spaces in between. I was unable to pick out our two operating transmitters at 101.9 and 107.1, but they are at legal part 15 power located a whole room away.
This new morning I went for the AM band, expecting little, because the antenna included with the SA is only about 12-inches telescopic.
But I did find evidence of AM activity. Most prominent was 1550kHz, a very tall spike coming from four feet away in the front window of the office. Next, I turned on 1680 AM and it produced a peak nearly as high coming from 37-feet away in the upper-management lounge.
I kept an eye on the 850kHz spot because a 5kW station was due to turn on only a mile from here, and right on time there it was. I could even watch their spike shoot up and down as it followed the Amplitude Modulations of the announcers voice.
Smaller spikes included 1120kHz, 1320kHz, 1430kHz and 1600kHz, owing to their power level and relative proximity to this location.
The next project will be the building of a loop antenna for the medium wave band, and that may not take long since it can be built from parts on hand.
Let’s head over to the cafe.
radio8z
Total posts : 0What do we want to do with an indoor antenna design? First and foremost we want the thing to radiate the maximum possible signal though constrained by physical limitations of indoor space.
The following are ideas which have not been tested by me but are offered to those who wish to do so.
Install a linear ground conductor with the transmitter “ground” connected to the center. In principle, this would provide for the necessary return current path to the transmitter and the net radiation from this “ground” should be zero.
Is it possible to build an antenna system which radiates the signal and doesn’t require a ground at all? Yes, but it may not be the most efficient approach. How about two 1.5 meter conductors arranged as a dipole with the transmitter in the center and each with a resonating loading coil?
Neither of these suggested systems may compete well with an outdoor system with radials but it may be that this is the best that can be done indoors and they just might give a decent signal range.
I would like to see this topic approached with a sense of adventure rather than a listing of reasons why it would not work.
Neil
Carl Blare
Total posts : 0Dear Neil:
No indoor antenna design will be left behind.
As these experiments unfold, we will try everything.
The resulting documentation will be available as it’s written at the link given above, and will be made available in the public domain for inclusion in the part15.us library.
Your mention of twin loading coils is very techno and will be fun to implement.
I just put my 2nd self-loaded coil to work on the Wintenna at 1550kHz, and my first self-loaded coil on the Quacker Oat box is stored with the Ramsey AM 25B.
RFB
Total posts : 0“I would like to see this topic approached with a sense of adventure rather than a listing of reasons why it would not work.”
….I
RFB
Carl Blare
Total posts : 0Neil’s # 1 Idea a few jumps back is reprinted here:
“Install a linear ground conductor with the transmitter “ground” connected to the center. In principle, this would provide for the necessary return current path to the transmitter and the net radiation from this “ground” should be zero.”
Aha! Yes sir! And that indeed is a “secret ingredient” that I recently learned on this website, in things said by Neil, rich and perhaps MRAM.
That is exactly what I now have on AM 1680, the AMT5000, serving bird bath and back fence.
It was the key to finally getting the signal up the hill to the mulch pile. But it is also an indoor antenna!
Half of my linear ground conductor leaves the building at foundation level and travels underground uphill, while the counter-portion runs through the basement, tie-wrapped with the I-beam.
Fuller details on these designs will be forth coming.
Carl Blare
Total posts : 0The first full day with Spectrum Analysis has been very part 15. Now the radio station has become real. It doesn’t need listeners, it needs that peak on the scope.
Finally I know what the radio engineers were doing with their interesting scopes while I served as a mere announcer.
I always thought they knew a special way to use an oscilloscope, and when I built a recording studio I had a scope used for aligning stereo tape heads on tape decks. I was sure that I could use the scope in a radio station some day.
I wonder if this spectrum analyzer would impress a lady. “Would you care to stop in to see some medium waves? It’s like etchings, only more wiggly.”
Rich
Total posts : 0Finally I know what the radio engineers were doing with their interesting scopes while I served as a mere announcer.
Both the disciplines of distribution and program content are needed to create a superior, or even a viable audience base with respect to contemporary, competitive sources. Even more so now, considering all of those sources available these days.
But probably _first_ come the program distribution channels (science), and then come the programs that they convey (art) — as first was shown by the dramatic development/growth of MW broadcast station audiences back in the 1920s and 1930s.
Carl Blare
Total posts : 0The radio horse did definitely come before the program cart, mixing a metaphor with a fact, as the technical radio instrument was first demonstrated, followed by the artistic minds who saw the chance for “theater in the air.”
No one invented a radio program prior to the development of radio transmission.
Commercial sales were done door-to-door and the musicians on phonograph records competed with their own hotel ballroom dance orchestras until they were saved by occasional movie jobs.
Pre-radio announcers accounted for the large number of railroad bums.
Carl Blare
Total posts : 0This may be on the slate for tomorrow, since the FM STL path down one-floor to the LPB CC transmitter is still in the multipath…..
As several of you have said, the vertical FM antenna above the CC transmitter is putting a null downward, so we need some horizontal signal, but need to keep a vertical signal for a 2nd path located on the same floor which does not have multipath.
I would like advance opinions about what to expect, but I’m going to find a piece of metal strong enough to bend into an “L-shape”, with equal legs.
One leg will point vertically, the other will face horizontally.
There are two ways to try it.
1.) Series fed — where the RF goes into the tip of the horizontal leg and flows up the L to the tip of the vertical section;
2.) Parallel fed – with the RF injected at the elbow of the “L”, putting the horizontal 180-degrees out of phase with the vertical.
I’m not sure how the phasing is done on a professional vertical/horizontal antenna, but I will watch this on the Spectrum Analyzer and compare both methods.
RFB
Total posts : 0One way would be to use a common cable tv splitter, and feed two dipoles, one vertical, one horizontal.
Situate the dipoles so that you have a cross. Or you can put the horizontal on the floor and the vertical above that at about 1/2 wavelength of F.
Should solve the multipath problem.
RFB
Carl Blare
Total posts : 0The dipoles sound like a very easy to do approach. I will include it in the testing plans.
But I am looking also for an opinion about my “L” proposal described above. I will be trying it for comparison with other methods.
RFB
Total posts : 0Might work if the TX your using had more than 11 nanowatts coming out of it.
A simple L is not going to get you dual polarization. More likely that will act like a standard vertical whip even with the lower horizontal element.
Separate the vertical and horizontal of the L so they are fed independently, then you will get your c-pol.
RFB
Carl Blare
Total posts : 0The C.Crane type of FM transmitter is most commonly used indoors in the attempt to provide wireless stereo audio to various locations within the dwelling.
The telescoping antenna on the C.Crane is 11″, nowhere near a reasonable fraction of a wavelength.
The part 15 rules on certified transmitters require using the installed antenna, any changes to the antenna make the certification invalid.
Strangely, the Wholehouse 2.0, a certified FM transmitter, has a stub of a wire at the RF output, a wire-connector, and a long wire, with a formula for calculating a full wavelength, which interestingly is about 3-meters. What’s obviously strange is that the user can cut his own antenna without losing certification.
We elected to hang a 1/2 wave vertical antenna from an indoor “art project” bamboo tower, and made it a four-element cage-monopole type.
Despite the advantage of the lengthier antenna, the Wholehouse does not perform any better than the C.Crane, indoor reception is great for about four feet and doesn’t go around corners or through walls.
None of that matters in our case, all we need is a solid link between the FM transmitter and two receivers which feed AM transmitters. Our vertical link located on the same floor works fine, but the downward link 1-floor below is riddled with multipath, because the bamboo tower puts a null toward the downward direction.
That explains why we are re-engineering the tower to provide a horizontal signal for downward thrust.
Questions about part 15 compliance are virtually moot in this scenario, because there is no outward penetration beyond the building walls.
Rich
Total posts : 0We elected to hang a 1/2 wave vertical antenna from an indoor “art project” bamboo tower, and made it a four-element cage-monopole type. … That explains why we are re-engineering the tower to provide a horizontal signal for downward thrust.
Acceptable results might be produced by inclining even a simple, linear, non-cage radiator so that the perpendicular bisector from that transmit antenna is directed toward the receive antenna on the lower floor.
RFB
Total posts : 0….use a simple piece of wire tilted towards the lower deck where you need more signal. Arrange it so that one angle looks below and the other looks up.
Worth a try.
RFB
Rich
Total posts : 0Inclining the perpendicular bisector of the receive antenna on the lower floor toward the transmit antenna also may be beneficial.
(edit) I see that RFB posted something similar a few minutes before I first posted the text above.
Carl Blare
Total posts : 0Earlier I described an “L” shape which seems to be the same thing being here proposed. Am I in tune?
And I agree, the receiving station down below needs also to be correctly “aimed”.
Rich
Total posts : 0Earlier I described an “L” shape which seems to be the same thing being here proposed. Am I in tune?
An L-shaped radiator doesn’t have the same radiation pattern as the linear (straight) radiator I described.
But nevertheless it might be useful in your situation, especially if the pattern of the receive antennas you need to serve are compatible with the radiation pattern of that transmit antenna.
Carl Blare
Total posts : 0Going back to what rich suggested I believe, to put it in other words, a straight wire is being described, but instead of being vertical, it would tilt toward the downward target, making it equi-distant between vertical and horizontal…..
The receiving antennas could be angled accordingly…..
Am I gaining speed?
Carl Blare
Total posts : 0Having taken a crash coarse in analyzing the spectrum analyzer, I actually found my FM whisper-signals.
The FM band on the scope looks like an insane cartoonist’s animated drawing of a city of high-rises bursting out of an empty field on either side.
By narrowing down the signals I first found 101.9 coming from the C.Crane, and it was harder to fish out 107.1 from the Wholehouse 2.0, which registered lower despite having a bigger antenna.
Once I had 107.1 singled out on the scope I cut all but one of the elements comprising the cage-monopole, and the power level remained the same on the scope.
Since then I’ve been trying to think of what metal I have to build a tilted straight antenna, and how to put that on the tower so the structure doesn’t tip over.
The Yagi idea is much better than the folded dipole that’s on the receiver. I think.
Carl Blare
Total posts : 0At first I “ran with the idea”, to use an expression.
Then I walked around the idea, and finally sat on it.
The “idea” was to build a straight-line antenna mounted in a tilted direction which would put signals both downward and backward; that is, toward the back of the house.
Mechanical realization of the idea seemed to be impeded by integration questions; that is, fitting it into indoor space so it wouldn’t poke somebody in the face or look like an avalanche in progress.
What was needed was a temporary quick-fix.
Down below at the LPB CC transmitter the Technics FM tuner has a signal-strength meter, which was showing a fluttering signal between 2 and 2.5 on a scale of 5. What I did was move the folded dipole until I captured a 4.5 signal on the meter.
We are now functional, probably compliant, and the tilting antenna can await a brain-storm as to how to make it stand there, tilting.
Carl Blare
Total posts : 0What the preceding entry illustrates, is something particular to indoor antenna design, that of making it part of the decor, without creating hazards or ugly “wife offending clutter”.
Rich’s idea of a linear antenna tilted so as to serve both downward and forward poles of transmission is simple to describe and imagine, but putting it in the room stumps the smartest interior design expert.
Contents of indoor rooms are mostly vertical or horizontal. Perhaps the back of chairs and sofas have some “lean”, but not much else. Well, dogs and people may tilt occasionally.
Getting to the point, the very heart of indoor antenna science/art consists of 50% technology/50% interior architecture.
This project, the design of indoor antennas for part 15 radio, will not accept a schlock approach. A “schlock” approach is that often taken by a short-cut artist with no social skills. Part 15 is a no schlock operation.
Carl Blare
Total posts : 0The geometry of antennas is on my mind tonight. They have towers that stand straight up. There are self supporting towers wide at the bottom narrow on top, but their geometry is for support, not RF efficiency.
FM antennas are more swirly, with curves and twirls to get that signal into the vertical and horizontal planes.
The cone antenna is an interesting combination of playroom geometrics.
But in part 15 the antennas tend to be straight up, side-to side, 2-dimensional at the most.
I am looking for 3-dimensional antenna designs. The helical “slinky toy” example is a start.
What else do we know about 3-D antenna geometry?
RFB
Total posts : 0
mram1500
Total posts : 0How about a Fractal antenna for improved bandwidth. Never seen one used below a few hundred megahertz but what the hey.
Carl Blare
Total posts : 0The tree is a natural example of a Fractal design, the way its branches head off at multiple directions and angles. In fact, a 10-foot tree might be the best possible example of a fractal configuration that could be the 3-D model for a Fractal part 15 antenna.
Perhaps a metal erector set would supply the parts that could be assembled in a Fractal array, insulated from the earth at the base.
Such a tree might serve the double use of being the annual Christmas tree, although festooning it with lights and decorations might detune it.
A 3-meter Fractal tree outdoors would attract the occasional bird.
Another indoor idea would be to build a clothes-tree with Fractal off-shoots, and a sign – “Not For Coats”.
Carl Blare
Total posts : 0At first I planned to use 1640 as the designated indoor antenna test frequency, but now I’m looking at 1710kHz, because of how clear it is.
The lower power levels allowed for 1710kHz may fall right in with an indoor antenna, which will be attenuated by passing through walls and at the outside location where an official field strength reading would be taken will most probably fall safely within 15.223, quoted here:
Operation in the band 1.705 – 10MHz
(a) The field strength of any emissions within this band shall not exceed 100 microvolts/meter at a distance of 30 meters.30 meters is around 100 feet and that’s way off the property.
Does this seem reasonable?
Rich
Total posts : 0Carl – You might want consider the rest of 15.223, as you find that appropriate:
However, if the bandwidth of the emission is less than 10% of the center frequency, the field strength shall not exceed 15 microvolts/meter or (the bandwidth of the device in kHz) divided by (the center frequency of the device in MHz) microvolts/meter at a distance of 30 meters, whichever is the higher level. For the purposes of this section, bandwidth is determined at the points 6 dB down from the modulated carrier. The emission limits in this paragraph are based on measurement instrumentation employing an average detector. The provisions in §15.35(b) for limiting peak emissions apply.
Carl Blare
Total posts : 0Yes, considering all of 15.223 is certainly appropriate.
If you will, please explain the portion you cited in light of the known character of a standard AM broadcast signal.
Thank you.
Rich
Total posts : 0It might be this part: However, if the bandwidth of the emission is less than 10% of the center frequency, the field strength shall not exceed 15 microvolts/meter or (the bandwidth of the device in kHz) divided by (the center frequency of the device in MHz) microvolts/meter at a distance of 30 meters, whichever is the higher level.
For consideration… the r-f bandwidth of a standard analog AM broadcast signal these days is less than 20 kHz, given the definition in FCC §15.223, and the current NRSC standard.
An r-f bandwidth of 20 kHz plugged in to the above quote yields 20/1.71 = 11.7 microvolts/meter as the result.
But also an r-f bandwidth of 20 kHz is less than 1.2% of a 1710 kHz center (carrier) frequency.
So by FCC §15.223, an unlicensed system operating with those parameters is FCC-compliant (if such is desired) as long as the maximum field measured 30 meters from its radiator does not exceed 15 microvolts/meter.
An unfortunate reality in this scenario is that a 1710 kHz field intensity of 15 microvolts/meter is well below the ambient r-f noise level in virtually all locations outside a screen room, let alone the interference-free r-f field intensity needed for useful reception by most consumer-grade AM broadcast receivers for that carrier frequency.
Added later: Even shorter path distances might not provide useful fields.
This is getting a bit technical, no doubt, but that is the requirement given in Part 15.
Carl Blare
Total posts : 0Rich, would it then be your advice that, although we are only planning to test antennas indoors in this particular discussion, we should stay away from 1710kHz as a test frequency?
I recall from previously having a number of different indoor antennas that some signal does escape, and for most people it would only be a guess as to how much power that actually is out at 30-meters.
Rich
Total posts : 0Hi, Carl –
That’s up to you, of course.
You wrote your guess that you will meet Part 15 when using an unlicensed AM transmit system indoors, and if so, then no problem.
But the FCC will doesn’t guess, they measure 🙂
None of this matters to me personally except as an educational project, and is offered only as a “heads up.”
RFB
Total posts : 0I seriously doubt any FCC field agents are cruising around neighborhoods at random measuring for someone tinkering with indoor antennas to make sure they are standing straight and feet together and eyes front with chest out and shoulders in and gut tucked.
Good lord, so what if his 1710 signal is above the limits. HE IS TESTING, NOT CONTINUOUSLY BROADCASTING!!
I do believe there is a provision in the rules for periodic tests at far greater power levels and field strengths.
Oh and one more thing, your right, the FCC does not guess, and yes they do measure, but they do not know what to measure or what to go looking for unless someone happens to say…complain enough to convince them that so so may not have their shirt tucked in and their gut is hanging out. :/
Just a heads up.
RFB
Rich
Total posts : 0RFB wrote: I do believe there is a provision in the rules for periodic tests at far greater power levels and field strengths.
This is an interesting belief, and very useful to those subject to FCC Rules — if you can provide legal documentation to prove its accuracy.
Hopefully you can, and will do so. And if not, probably you should retract this post of your belief.
Otherwise your post could lead others into the risk of FCC citations, would you not agree?
Carl Blare
Total posts : 0My remarks right now about the status of 1710 kHz is not editorial commentary in protest of existing rules. It’s more of a passing observation on this space flight known as life.
1710, empty and unused on all modern AM radio receivers, reminds me of our public parks. Parks are “public space” and 1710 is on the “public airwaves.
But there’s no parking in the park after 10 PM, there’s a park curfew; sleeping or camping overnight is an arrestable offense. The public is not allowed in the park during arbitrary hours.
1710 is not in use. It could come in handy for a small time part 15 broadcaster. But it’s closed, albeit abandoned.
Some rules make the gentry class seem a little too tightly sphinctered, but the species in general isn’t all that successful anyway, so I think I’ll use 1640 for indoor testing.
RFB
Total posts : 0My belief is this. It does not matter what I believe, does it.
However the belief that you wish to throw out here is that if anyone so much as steps 1 nanoflea volt or watt beyond the width of a hair past that black and white writing on the wall, they had better just turn themselves in and declare themselves as the biggest baddest rule violators ever to dabble with radio.
I believe however, that if you go look at the entire Part 15 section containing the various bands, you will see provisions in some of them that allow for periodic transmissions with much greater field strengths.
No one said anything that there was a specific provision for the MW band. I simply said that there are provisions in Part 15. You can find them I am sure of that..as I am sure and believe that you are aware of those provisions as well.
So I guess even researching indoor antennas has to be so scrutinized down to the nth decimal place within our own homes now.
All the while one of your licensed goody good doers who currently has 4 STL violations spanning 16 years along with 2 other outstanding NAL’s for two other cities and has no CAP at ANY of the stations, just got a get out of jail free card (3 of them) from the FCC, 3 brand new STL licenses which 3 of those 4 STL violations ARE THE SAME STL.
Don’t play no game I can’t win, you will be the only player.
Do you want to see my papers too?
You know what, why don’t you go call these licensed to violate law abiding station owners and point out some rules to them.
Since I can still add to this post much later, I will. Forgive me for the harsh stance tonight. I have stood for playing by the rules all my life. Devoted a lot of resources into having the right tools and knowledge to see me through. I was raised to be respectful, even to those whom I disagree with or even do not like. It is that which gives me reason to apologize to Rich for being harsh. Though the system isn’t perfect, it certainly is not so crippled as to let by such huge violations and reward that with new licenses on STL’s that are currently tagged with NAL’s, amongst 2 other past and still outstanding NAL’s and there is a lot more I guarantee everyone.
It is so frustrating, seeing something that you have wanted all your life, be in someone else’s hands where said someone doesn’t give a flip about FCC rules or licenses or real radio broadcasting so much to ruin and seriously affect an entire market for the other stations and here I am, with my little Part 15 stations applying REAL broadcast industry standards and procedures to their operations and technical specifications to 209, 221 and 239. I invested a lot of $$$$ on proper test gear to ensure they operate within the rules, and to add to it, reading someone quote to me and other Part 15 operators about functionally compliant and etc etc.
Does anyone else understand the level of “close to home” impact this is having here, not just with the radio scene here in Casper, but also directly impacting me, and other people who were unfortunate to get a dose of the owner’s care and love for radio. Hint, he is NO broadcaster.
Anyway, back to indoor antenna research. Carl, I have to ask you, would you really give some serious consideration to working with the hexagon pattern? I think you might find something very interesting about it and resonating it with RF.
RFB
RFB
Total posts : 0Yep, its pretty much pointless to be doing indoor antenna research and using 1710 as the testing frequency with those lower limits than that of 530 to 1705.
I would select a frequency for testing that is mid-range between 1250khz and 1700khz. There is bound to be one in there somewhere that will be close to what most 219’ers are using to do the antenna research.
What..no takes on my hexagon antenna suggestion?
You should try it. I have. Nope, ain’t gonna tell! :p
RFB
Ken Norris
Total posts : 0“The tree is a natural example of a Fractal design”
There are literally hundreds of papers written on this subject. Both the military and cell phone makers are very interested in them
The problem is one of time and materials. I worked out a scaled design for a circular fractal antenna for LP AM radio. However, the sizes I needed for AM BCB would be prohibitively expensive, and involved a heckuvva lot of work to make the parts, lots of soldering, etc.
The primary use of fractal antennas is in wideband microwave areas, which is why cellphone mfrs and military are interested. E.g., “smart” phones have to work on several different frequency bands … obviously you don’t want to put multiple antenna systems in them, so the wideband characteristics of fractal antennas are a good solution, especially as one can be made using industry-standard PCBs.
RFB
Total posts : 0A very huge difference between fractal antennas used in Ghz compared to Khz.
RFB
Carl Blare
Total posts : 0….tried fractal ground arrays?
You could bury one heck of a “tree” pattern made from wire.
PhilB
Total posts : 0I certainly don’t want to throw water on any antenna experiments, but an indoor antenna is a real unpredictable beast.
An indoor antenna is surrounded by aliens! Electrical wiring, plumbing, possible metal studs, possible metallic siding, etc. are MAJOR obstacles to the RF signal.
Additionally, the RF ground path is almost totally unpredictable, and probably will be poor in relation to the goal of providing a low loss RF ground counterpoise.
A long baseboard ground wire may provide a good counterpoise, much in the fashion of elevated radials for an outdoor antenna, but you are still contending with the huge effect of the shielding cage of the house.
It would be a welcome event to hear from anyone who has had meaningful success with an indoor antenna that ranges a significant amount beyond the house.
Ken Norris
Total posts : 0“It would be a welcome event to hear from anyone who has had meaningful success with an indoor antenna that ranges a significant amount beyond the house.”
In another thread somewhere (which I can’t seem to find at the moment … I’ll try later if I remember), I told of using a TH v.5 tx with the stock wire antenna tucked into an arched wood window frame from inside, The darned thing was quite listenable at 500 ft. from the house, and in one direction over a block behind the house and down that street to the high school, about 350 yards, and could be heard all the way down to Spring St. (our “Main St.”) … and that just after sunset … but it got pretty noisy a little later.
RFB
Total posts : 0“It would be a welcome event to hear from anyone who has had meaningful success with an indoor antenna that ranges a significant amount beyond the house.”
As Ken noted, a TH using the supplied 3 meter long wire strung vertically along a wall, by itself can cover 500+ feet from the home easily. And that is with the TH and wire antenna INSIDE the house.
Even your 5K unit with a simple wire can shoot the signal 6 houses down the block and over into the next block, all with the 5k set up indoors with that simple wire.
But I think you know that already.
RFB
Carl Blare
Total posts : 0The Indoor Antenna page linked at the start of this thread has yet to be updated from its very undone blankness, but there is now something to add to the page.
In various other threads we have discussed ground radials and other aspects, and there’s now enough information to document one of our indoor antennas.
Using the internal AMT3000 inductors and a baseboard floating ground we achieved 69 dBm, up from something in the 50 dBm range from earlier.
But tonight we installed and tuned our truangular hand-wound loading coil and have achieved a record 71 dBm on the Spectrum Analyzer.
All the details about this experimental antenna will be written up and published as time goes by.
Right away we move to the next indoor antenna, different in many ways from the one just completed.
RFB
Total posts : 0“Right away we move to the next indoor antenna, different in many ways from the one just completed.”
Looking forward to it!
RFB
MICRO1700
Total posts : 0I have been completely involved
with family/home stuff, as you know.HOWEVER, I am still looking from
“the outside -in” to what is going
on here.I can’t really contribute to discussions at
the moment. I miss that.Also, I can see that you guys are
having some “spirited discussions”
regarding THIS subject. I haven’t
really paid too much attention to
what’s been going on here – until
this morning on this thread.I can see that I miss the “spirited
discussions,” too.Very Best Wishes,
Bruce, Monitoring From West Hartford, CT
Carl Blare
Total posts : 0Very glad you checked in Bruce!
We are holding your place here at the part15 site, keep checking back as best you can!
mram1500
Total posts : 0Yes, the big boys get away with murder, as RFB states, with their numerous violations. And when they are called on the carpet with big fines it would seem they laugh it off according to the discussions here and elsewhere.
They can afford to do that, big money and all.
That’s the major difference. I can’t take the chance they do because one oops could wipe me out.
Now, I really don’t believe that will happen to me because I operate within the rules to the best of my knowledge (ATU and all you know.)
So, relax everyone. Unless you are burning a hole through the sky, blatantly in violation, I don’t believe anyone will bother you.
If they do, as Lefty says, be nice, talk it over and finally do what is expected of you. And if you still receive a NAL for $17,000/day, perhaps by then we’ll have a defense fund to bail you out.
Carl Blare
Total posts : 0Good idea the defense fund for part 15 members.
Also, can we have a retirement center? I recently heard that a retirement center for aging musicians has been started in New Orleans, and there’s also one for old movie actors in Hollywood.
kc8gpd
Total posts : 0the masons have a retirement center here where i love and it’s one of the biggest retirement homes around.
MICRO1700
Total posts : 0Wow. RFB, you’ve really got me going
there.I can’t remember the robot from “Lost
In Space” saying anything like that,
or any robot/android/computer from
Star Trek.I can remember some other Sci Fi shows
with robots in them, but still:I draw a complete blank.
Best Wishes,
Bruce, GNAT 90.9, SLUG 88.3
RFB
Total posts : 0The robot could fly by a back mounted rocket pack.
It had an ancient Egyptian king’s headdress.
It could shoot missiles from it’s fingertips.
It could shoot beams from it’s eyes that would neutralize anything electrical.
It took on the “Gargoil” leader and rocketed both the leader and himself to a final demise with a collision into an asteroid.
Imagine that robot as an antenna, or holding a 3 meter antenna up in the air for you! 😉
RFB
Carl Blare
Total posts : 0Using an LED (light emmiting diode) a tight beam of light would shoot three-meters from a one-eyed robot, be reflected back by an active mirror.
An active mirror is defined as a mirror that would send the return reflections at a rate of 1550kHz.
The 3-meter beam of pulsating light (1550kHz) would be amplitude modulated with very pleasant country western music from the 1950s.
A new antenna type is born.
Carl Blare
Total posts : 0The indoor baseboard ground idea, stringing wire along the baseboard of a room to compensate for lack of a true ground point, works in one way.
It allows bringing the indoor antenna to resonance according to the instructions supplied for using a loading coil with the AMT3000.
But, as RFB explained, the fact that baseboards make many right angles throughout the house, depletes the effectiveness that would result from a straight line 2-element ground radial.
The Spectrum Analyzer gives a reading of 70dBm when the antenna is resonant and the transmitter grounded to the center point of a 48-foot baseboard wire.
Trying to boost the dBm to a higher level, I added 20-feet of wire to one side of the baseboard wire, which I thought would resonate and build on the output, but it did the reverse: the output dropped to 66dBm. Retuning the transmitter output by trying other coil windings did not improve on that loss.
We will often remind the reader that indoor antennas will always be inefficient, we are simply trying to improve on the result available.
Ken Norris
Total posts : 0
Ken Norris
Total posts : 0“We will often remind the reader that indoor antennas will always be inefficient, we are simply trying to improve on the result available.”
Well, the ‘locals’ in this group have said loop antennas (magnetic rather than electric) won’t work with the low power we have to work with, but I think with a properly-designed matching network and coupler, and large diameter copper refrigeration pipe attached right to the TX at its antenna connection (no loss, the coupled antenna 3′ in diameter)..
It will take a fair chunk more engineering and running formulas, especially for skin effect on the matching network, but I really believe an indoor system like that should work quite well.
It will be relatively directional compared to an electric stick, so it will need to be oriented to serve the target audience.
Also, I really want to experiment with the “loop that isn’t a loop” antenna idea … i.e., a 1″ copper pipe bent to approx 3′ diameter, with a loading coil inductor att’d AND connected to the pipe at one end, but att’d and NOT connected at the other end.
An apartment-dweller could set up one of these as an art-object if done right. I’ve had some visions of what it might look like.
Carl Blare
Total posts : 0I like your loop antenna vision, Ken Norris, and that it could be made to look attractive as an art work makes it very desirable for indoors.
I have the unproven and perhaps mistaken thought that loop antennas for transmission have been found undesirable by experimenters at medium and high power, and not by low power experimentation.
The directional factor might prove useful so long as the antenna can be placed in a best location.
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