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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.
Total posts : 45366Whereas 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.”
Total posts : 45366You 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
Total posts : 45366It 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.
Total posts : 45366Well 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
Total posts : 45366Years 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
Total posts : 45366I 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
Total posts : 45366The 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.
Total posts : 45366““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
Total posts : 45366A 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
Total posts : 45366Quick 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!”
Total posts : 45366Sounds great! Functionally compliant? What exactly is that anyway?
So many different angles to one simple thing of compliance. Amazing! 😉
RFB
Total posts : 45366Thought 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?
Total posts : 45366“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
Total posts : 45366I 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.
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