Test question: In this case, which is considered the final stage?
Well given an antenna tuner and coax cannot produce any RF signal on its own, as well as the wire or rod or coil antenna, that leaves only one thing...
...the final RF amplifier stage in the transmitter.
The 100mW refers to the final stage current, not actual RF power output. In the practical sense...the most mustard mustered with a well designed final stage might produce maybe 50-70mW of actual RF power.
But the previous question regarding the coax length from the transmitter is an interesting one where we see certification on the TH units with an FCC ID number on it and the output connector for connecting a coax which feeds a tuner unit then a wire....then we have the Rangemaster and ProCaster units and their FCC certification ID numbers, and those cannot have a coax.
In another thread I spoke of the mish mash confusion within the rules and how I believe that was done on purpose. I gave the frequencies listed for 15.209 thru 221 which is 525-1705. Those two extremes do NOT fall within the FCC specified standard of the 10Khz channel spacing for the MW band.
Confusing to say the least. Then there is the ground thing, the coil thing, the choke thing, the lead thing, the hight thing, the top hat thing,.....did I miss anything?
RFB
The talking house transmitter has a problem that's commonly known as FM'ing. The frequency is not stable and if you listen in the FM mode as I have, it sounds pretty good. 🙂 In AM the frequency variation is not too noticable. In SSB the carrier shifting produces the garbled sound you hear. Hope this helps.
Confusing to say the least. Then there is the ground thing, the coil thing, the choke thing, the lead thing, the hight thing, the top hat thing,.....did I miss anything? RFB
Yes confusion reigns. I would say try your best and if no one complains and your field strength is not causing any one grief (especially commercial stations) or hams (with splatter), you are good to go. The tree falling in a forest makes no sound if no one is there to hear it kind of thing.
The splatter actually bothers me because I do SWL. However no one in the area does SWL. I have not checked the range of the splatter, but it can't be more than the primary MW Freq. With on 30 feet (not meters) it is impressive. I know some folks put a low pass chebyshev filter or brick wall on their feed line. If you want to be stealth that might be a good idea to make sure your signal is as clean and splatter free as possible. You don't want to PO a Ham and his 80 meter rag chewing enjoyment. Although it would be hard to screw up 3.5-3.9 Mhz with harmonics from MW band if you stick to a Freq higher than 1.3 Mhz. Also the ham would have to live next door or across the street.
Again I am not saying to be cavalier or flagrantly violated any CFR's, but stuff happens. I have an approved TH and if I get an approved TH ATU. I am good to go. Now why if I duplicate that design DIY home brew would it not be acceptable, ie the coaxial feed line? I personally think the Part 15 restrictions are kind of fun to work with, aiming for max efficiency, while staying legal. However you have to talk about what is a No-No to do that. If you want range or don't care about legality, as some do, build a tube transmitter and crank the plate voltage up, and run 250' of wire. There is a lot more of that going on than people using coaxial from their 100 mW transmitter to a legal 3 meter antenna with a ground wire that is 2 inches too long.
PS thanks for the tip on the AM stereo board. I checked it out and it looks nice. The gent has already answered my questions. It makes more sense to put something like this outside than the big TH box. It is interesting it uses programmable crystals. Never seen that before. However nice the TH is to have variable station tuning with button and digital display, in all intents and purpose a single channel rig is better.
Try taking your SW radio out of the induction field and see if you still hear the harmonics or splatter. It could be your SW radio front end is just overloaded.
I put my TH on a commercial Motorola Station Monitor and the harmonic output was well within limits. Even so, my SW radio picks it up at harmonically related frequencies. But, I don't hear "splatter" more than one channel away.
Now I'm wondering if maybe it's less than 100mw due to cable loss.
I agree the coaxial loss is not a bonus. The bonus is not having your precious transmitter out in the weather. However for a short run with high quality coaxial at MW Freqs, loss should be small. However all things being equal, it is not a range increasing idea by it self.
I don't have a true RF milli-watt or RF milli-volt meter. However using a scope and 50 ohms the TH has most definitely over 2.25 mV RMS. TH (now Radio Systems) swears they all test in the 100 mW. That may be true at 1700 Khz for some units (remember they vary), but at lower Freqs the power does increase (dramatically) as you tune down. This is confirmed by another TH user I correspond with. It's Part 15 approved.
I just did my walking test with a KA1103 radio in hand. On 1700 Khz I get about 140 feet. On 600 Khz I get 190 feet. When I give range, it is when the signal strength "S-meter goes from full 9 bars (4 of 4 steps) to 6 bars (3 of 4). It's still listenable. Usually right before it switches from 9 to 6 some static (1 out of 5) is creeping in. I estimated with my HP 8640B, the KA1103 is "S-meter" flips between 9/6 bars at about 90 uV/m, give or take. Even though the sine wave looks crummy on the scope, at lower Freqs it still sounds fine. I am more driven by avail Freqs and local and DX noise. Of course making an antenna for higher Freqs is easier.
Again no one I know has had it on a real honest RF Radio Test monitor that measures RF (milliwatts) power accurately. I can say the sine wave gets quite distorted at lower Freqs I recall, where the higher freqs look OK, with some slight distortion or harmonics going on. Down low it looks ugly.
BTW on 1380 Khz I splatter every 1380 Khz up 11040 Khz. Impressive! It needs some serious filtering. I was scanning SW and came across 2760 Khz and heard this fantastic music. Wow coming in so clear.... it took me a few seconds (ok a minute) to realize it was my splatter. This is with in 30 feet (not meters) of the antenna. It is fine as long as no Ham lives next door.
I wounder if they have more power to account for all the loss in the coaxial and matching or tuning circuits of their ATU to get 100 mW at the ATU's 102" CB antenna vertical whip? Lets say it is making 140 mW to 290 mW. At best the efficiency of an antenna has to be less than 100/140= 71%. 100/290 = 34% would be optimistic at 600 Khz with a 9 and a half foot stick. So range is not going up with lower Freqs when I last checked, but the RMS volts are on the scope.
You need more out of your "RF Final" (transistor) to get 100 mW at the base of the antenna, withstanding coaxial feed line and antenna tuning, as non radiating elements. Not to be cavalier, this is just for discussion sakes. (My lawyer told me to say that.)
The "tuning" circuit, capacitor or Pi network, some matching is not radiating. If you want 100 mW out of that contraption, you need more than 100 mW going into it. Some might argue the loading coil is not part of the radiating element and thus can have 100 mW out at the base of the radiating element. A loading coil can be as short as 5" turns. So a 102" whip gives you 16" for ground and loading coil.
The field strength rule at 30 meters is 24000/Freq Khz, in units of micro-volts or uV/m? You can have over 3 times the field strength at lower freqs than higher. Why? That tracks what the TH power does, the power triples from high to low.
FEED LINE... I say the TH ATU has precedence, in legal talk. If it's good for them to use coaxial, it should be good for any amateur installation? As I say it is not a range booster to use coaxial by itself. Is that not the BOTTOM LINE.... not causing interference is the golden rule, while meeting the "spirit" of the regulation.
it's just a long shielded wire (standard 75Ω TV coaxial cable) to the tuner.
Actually they say it is 50 ohm but the ATU kit is said to be supplied with RG-6, which is 75 ohms. Cheap RG-59 TV coaxial is junk. Any way I don't know if the F connector is 50 or 75 ohms, but I called them. They told me 50 ohms. Why? Don't know. The manual does not say but I have heard 50 ohms more than once. Any one know for sure?
Yes it's definitely a near field thing, but weird thing is on 600 Khz and 1700 Khz it seems to be a non issue or less of an issue. You have to almost be on top of it to get one harmonic at most. However the Freq I was favoring 1380 Khz is noticeably more sensitive. On 2760 Khz it goes non existent at about 60 feet, but at 30 feet it's strong, keeping in mind sensitive SW receiver. On 4140 Khz about 30 feet to non existent, ~10 feet to hear it well. If near the antenna, 10-15 feet, I can get up to 6th harmonic. It's no big deal, but I was kind of surprised. Fun with EM RF. However I can see if you have a good outdoor setup and a Ham neighbor some low-pass filtering might be in order.
Splatter....the voodoo of AM. No doubt this would wreak havoc with a SWL who has a hefty high gain beam on a mast sitting on a rotor. I would also state that unless you got one of them 9 grand AM splatter measuring devices, do NOT consider the splatter off a SSB receiver or what you are hearing as an accurate measurement or what actually is being spat out by these TH units! There is specific measuring equipment used to check AM sites for splatter, and they are not some off the shelf SSB receiver or general communications monitor!
That is interesting the box favors the low frequencies and increases RMS. I may just buy one of these things and put it on the operating table..see whats going on there. But considering these tune the entire band, they had to build it with a very wide bandwidth tolerance so the thing would at least put out a half way decent amount of signal across the band. And naturally it would have a point somewhere on the band (preferably in the middle of it all) where it is at peak and slope down on either side.
I once did try a feed line to my 3 meter setup. The coax was RG-8, about 20 feet worth. Not any major deal at 1.670Mhz.....if the power was a watt or more..but at flea power...might as well just terminate the output of the TX with a resistor. The problem is the fact that because there is a coax of some length carrying that flea level energy....the coax itself tends to "eat" some of the signal. The signal gets absorbed by the coax itself and by the time it reaches the loading coil outside, even with a cap across the coil to peak and tweak...the signal was considerably less on the field strength reading at 93 feet.
I too do not like having the TX sitting outside, even in a weather proof box. But considering those darn confusing rules...well I decided to incorporate temperature control inside the box. The "puppy hut"..as I call it...uses a 20 watt, 10 ohm cement resistor attached to a heat sink with large fins. Controlled with a simple diode/op amp arrangement, it switches in a relay and feeds that resistor with 15 volts from a separate supply and helps keep the stuff inside nice and warm during our -20 winter temps that sport wind chills as low as -40.
The radiating element at the bottom is open-ended so at least a little of that heat will rise and travel up the stick, helping to keep ice from building up....sort of a poor man's de-icer.
PS thanks for the tip on the AM stereo board.
Your welcome. Chris is very up front and honest. He is a great person to get to know. With some modifications, you can make those boards frequency agile by using an external PLL kit for about 30 bucks running an oscillator. I did that to one of my boards just for the fun of it. It works really well. The major modification you have to do is with the oscillator circuit. It is configured with two transistors, one as the oscillator, the other as a buffer/switch booster, then feeds the divider chip. Because of that arrangement, your signal from the agile oscillator must be of a significant level to drive the divider chip. Not any big task really. However unless you really have to change frequencies, its best to have a single frequency unit no matter what kind of TX it is. And even if you do have to change frequencies, with the programmable oscillator units at less than 7 bucks, order up a few to cover the frequencies you need and simply swap them out. His boards all have the proper socket for those programmable oscillators.
I will post a picture of my primary LPB TX-2-20 CC transmitter that is currently on air using his board as the exciter and it uses one of these programmable oscillators.
(Edited to add picture link)
Here is the link to the picture of the LPB TX 2-20 C-CUFF C-QUAM Transmitter currently on air. Key points are identified in black or white font.
For the curious on how these boards sound....here you go. 🙂
http://krocksradioone.com/files/AMSTEREO1670soundsample.mp3
The receiver used is the Sony SRF-42.
RFB
Once again, it's a bureaucracy. Requires lots of interpretive latitude, or field agents who have also passed the bar.
"Confusing to say the least. Then there is the ground thing, the coil thing, the choke thing, the lead thing, the hight thing, the top hat thing,.....did I miss anything?"
I want to build a magnetic loop antenna with a matching network, as a possible solution for apartment dwellers. The rules don't talk about anything but vertical electric monopole sticks.
I want to build a magnetic loop antenna with a matching network, as a possible solution for apartment dwellers. The rules don't talk about anything but vertical electric monopole sticks.
On the following url link you can get an idea for just such an antenna. This company makes loop antennas and you can specify the center frequency and they will build it to your specs.
http://www.antennas.us/store/p/326-LL-1001-396-600-1600-kHz-Omni-Antenna-AM-Antenna-.html
This antenna can handle up to 1 watt maximum in transmit mode. They also have one that can handle 10 watts maximum in transmit mode.
All of the specifications are on the website page in the link above.
RFB
The talking house transmitter has a problem that's commonly known as FM'ing
This is due to poor design factors. There should not be ANY FM going on in an AM rig, no matter how big or small. Same is true with an FM rig, no AM at all.
This brings into question regarding the TH modulation scheme. Either the modulation design is of incredibly elementary level (pre beginner), or done on purpose to make cheap.
I would say its the latter...simple design for a simple device doing a simple task, thus cheaply made.
Just going over the patent schematic..it appears that the entire RF section and PLL section could use a total re-design.
For starters, I would not have used direct collector modulation. There is not enough circuit isolation between that stage and the RF generating circuitry as well as its PLL. There is why you get FM. Both audio and the PLL frequency adjusting pulses are FM'ing the carrier. ICK!!!!
I would have used a balanced modulator, even if that comprised of a simple diode bridge comprised of 4 1n4001's and some caps and biasing resistor. Basically that is what a balanced modulator is.
Or incorporated an actual (and extremely cheap) balanced modulator IC. The IC alone would provide enough isolation between the oscillator, its PLL and the final stage, thus preventing any impedance swings on the output from messing with the RF generating circuits.
As to the PLL, single ended PLL design is usually good enough for devices such as the TH, seems to keep the frequency within tolerance for all receivers. But as described here in the thread....its warbling the carrier in sync with those PLL pulses. Not enough DC isolation and too much AC coupling between the PLL and oscillator. ICK!!!!
Yep...would make a great weekend tear apart, look and see, try a few ideas project.
RFB
This company makes loop antennas and you can specify the center frequency and they will build it to your specs.
This is the custom one:
http://www.antennas.us/store/p/327-LL-1001-396-CF-Custom-Tuned-Omni-Antenna.html
I WANT ONE... They are $143 for one, $106 for 5, $99 for 10. Any one want a group order. I would love to know how well they work on 100 mW. The wide-band version is cheaper, $108 for one, but apparently needs a Watt or more.
Using my HP signal Gen and my Terk AM Adv 9" loop for transmitting. I was not very impressive, nor did I expect to be. However a magnetic loop would be the way to go, but the Regs don't say, so in theory you could make a loop 3 meter in diameter? Even if you went on circumference, that would be a one meter loop. Of course the ideal circumference would be at least 71 feet or 22.6 feet diameter. If you want range (not omnidirectional) the loop would be cool. The web is full of magnetic transmitting loop designs, usually copper tube with an air capacitor, not much more.
Yep...would make a great weekend tear apart, look and see, try a few ideas project.
RFB I hope you do get a TH to experiment on, come up with some mods. Although it is "ICK!!!!", would you say that it's worse to have AM on a FM radio than a little FM on a AM transmitter? It seems the mathematics of mixed FM and AM is too complex to just casually discuss, but it seems that an AM radio will ignore FM, if the deviation is a small fraction of the bandwidth (8 Khz to 10 Khz). Ideal? No it is "ICK!!!" to be sure.
Actually the company will custom the lower power model as well. I bought one and tried 100mW on it at 1.670Mhz. It worked really good and was very omni-directional. These would be a great choice for an antenna to expand your station's coverage with added transmitter locations. Small and are far easier to install at just about any proposed site, and they do not require a counterpoise, which makes the extension station site a snap to put on the air.
I am considering a TH unit just to see what all the hub bub is all about with these things. It seems that from one unit to another there are considerable variances in specifications and performance. Curious to say the least.
Questionable quality control perhaps? I'm not sure. They seem to be quite popular though in the Part 15 community.
Is it the price that makes them popular? Is it the frequency display? The auto-antenna tuner? The option of having a coax to an outside antenna with an FCC certification number? All of the above maybe?
The FM'ing issue. An AM radio receiver will indeed ignore the FM modulation of audio somewhat, but will affect things like a receiver's AGC and noise canceling circuitry. The receiver is looking for a stable carrier that changes in amplitude. But if that signal is also changing in frequency while changing amplitude, that is what will affect the receivers AGC and noise canceling. Not by much but that little affect might be the make or break to a signal at a distance from the TX.
As described by some of the members, most of their observations have been in close proximity to the TH unit, not at a distance. It would be interesting to measure the artifacts at a distance and see in comparison to another unit that has no FM artifacts at the same signal levels and distance.
For a mono AM transmission, the FM artifacts will have some effect, however for a stereo AM signal, that will muck up the 25hz pilot tone with a 5hz or other frequency shift taking place due to FM'ing. I would take a wild guess and suspect that what would be heard would be a phase shifting between the left and right channels, as AM stereo relies on quadrature modulation where the L-R stereo information is 90* of phase from the L+R information. Audio in AM stereo transmitters takes two paths in the transmitter and those two paths have to be exactly 90* of each other or you end up with phase shifting and null of the audio, especially on mono receivers despite the fact that envelope detectors are used.
For FM with AM artifacts, that too would cause issues with a stereo transmission. It would affect the channel separation and obviously cause the carrier to change amplitude, which would wreak havoc on an amplifier meant to amplify a constant carrier level, not a carrier changing amplitude as well as create distortion in the audio. If a peak detector were connected to an FM transmitter with AM artifacts, that peak detector would bounce with the modulation instead of being steady. That could result in blowing out finals of the amplifier.
Remember the old BA1404 chip, the "FM station on a chip" chip. Those things had such poor performance even with heavy modifications because they had terrible AM artifacts inherent to the chip. Then came the BH1415 and BH1417, and those were a serious improvement and do not have anywhere near the AM artifact issues, and is why they produce such a great stereo signal on FM.
Yes either case, AM on FM and FM on AM is not good. For the TH units and its designed purpose...the artifacts seem to not cause them too much of a problem, but those issues are there and deserve at least some investigation into them for possible fixes.
RFB
Any way I don't know if the F connector is 50 or 75 ohms
Actually it is not the connector that establishes the impedance. Its the circuitry before the connector that determines impedance.
For example, some transmitter kits use an RCA connector. Well those RCA connectors were at one time primarily used for line level audio, with an impedance of 10K ohms. But in the SSTran for example, that output is 50 ohms via that same RCA style connector.
There are certain types of connectors that are preferable to use at certain impedance ranges as well as frequency ranges. You would not want to use an RCA connector on a TX that transmits a 2Ghz signal for sure, rather an N connector or BNC would be the preferred type.
RFB
I do equate the 'F' terminal with consumer electronics, TV and FM radio, which are typically 75 ohm, but I realize an 'F' connector is not only 75 ohm. They should label it on the TH. The confusing part, I thought they supplied RG-6 with their outdoor antenna or ATU, which is 75 ohm coaxial. I don't care for 'F' or RCA jacks for antenna. I'm going to replace the 'F' jack for a BNC on Talking House. My TenTec RX320D uses RCA jack for an antenna, which I don't care for either.
Let me ask you RFB, do you have some basic 'ball park' formulas or favorite online calculator to estimate range at the MW band. I want to backwards calculate the unknown emitted power (EPR) for a given field strength (90 uV/m or -67.9 dB) and distance 130 feet or about 40 meters.
Let me ask you RFB, do you have some basic 'ball park' formulas or favorite online calculator to estimate range at the MW band.
I am sure there probably is an online program somewhere that will do what your looking for. However I am not familiar with any as I use a program written way back in the day of DOS 4. I have a dedicated PC that runs DOS 5.0 to run this program as they will not run properly on a Windows platform. It will calculate theoretical range given the input of power level, antenna height and length, polarization, impedance, center of radiation, frequency and modulation type.
It is one of several programs given to me by a fellow engineer and is the best set of programs that any RF engineer could ever have in their arsenal of tools and test gear.
Back then these programs came in individual packages and each one cost over 400 bucks each..plus or minus a few bucks. My engineer friend had purchased them for his consulting business and passed them on to me after he retired. He is no longer with us as he passed away in 1998, rest in peace my old friend.
Im sure if you google for such an online program there should be some results.
RFB