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Build your own FCC Part 15 compliant 100 mW Motorola C-Quam AM Stereo transmitter. This is Sean Cuthbert’s latest PLL version with pushbutton digital tuning (previous versions had DIP switches or analog tuning):
http://www.ebay.com/itm/131904130748
Total posts : 45366There will be a few members excited about this kit. It will fill a void where, from what I having been reading, no 100mW AM stareo transmitter has been available.
Looking forward to hearing about experience with this.
Total posts : 45366I am very tempted to snag that unit and see what is all about. AM stereo is a goal of mine here at the Jacksboro Radio Network. Alas, I do have many goals.
Someone with some time to build a kit and a few extra bucks, needs to bring this unit into the fold with a report!
Total posts : 45366Like to see how this does. Does it cover the whole band or only part like the old digital C-Quam AM Stereo one did?
Total posts : 45366Great! I’ve been seeing transmitters that look like this for a few years, same cases and knobs, with the perf board experimenter’s board being used. They should consider getting fibre boards made, it’s pretty cheap to do that these days, and much easier for the builder!
It came out a few years ago, and I saw the video that shows the evolution of the circuit on the guy’s bench, to the final product. The first transmitters came from outside of the US, but now they’ve been coming from the West coast for the past year.
I notice his synthesizer is an older chip, the big chip by Motorola. I guess he has a reason for using it, but I didn’t know those were still being produced.
I’ve wanted to experiment with AM stereo too, and I’ve tried to find a schematic for a real working unit to get started, but haven’t been able to find anything solid state or IC based, just one done with tubes by a clever technician!
Where are circuit diagrams for transmitters like the old Alfredo Lite and others that have come out since then? Circuit diagrams for everything seem to be posted, and there are schematics for so many AM transmitters, but why not AM stereo ones?
Total posts : 45366Looks good and a whole lot less $$$ than others. $129 and a whole lot of bang for the buck.
Not good for me here in Canada as it is not certified, just “meets” rules…not good here. I asked Industry Canada(IC) about this and got in writing that if it doesn’t have an IC label and number it has to be tested by a IC approved test facility. You can be told you can’t use it even if you are obeying all ground and antenna rules and power limits. Same with FM. Wonder how this would stand up against others like the Procaster?
Mark
Total posts : 45366I have the dip switch version of that c-quam transmitter, and i also have the Aspisys ASMAX 1 transmitter, and today just received the Cyprus c-quam transmitter.
Regarding the perf board transmitter from california, the major problem i have with it is microphonic phase mod from the coil of the vco.
Also the agc circuit is basic, and audio is fairly low, but sounds ok.
Also the phase modulator looks not to be the full vector modulator, as in the proper c-quam spec, but seems to work ok.The ASMAX 1 has no microphonics, but the pilot tone is poorly filtered, and this adds lf noise to the audio on my hifi setup, so i have added a 25hz bandpass filter to improve it.
On both above units i bypass any audio filtering, as i am using proper c-quam based audio processing in to the transmitters, also both these transmitters tested here have some modulation evelope assymetry on the scope.
The Cyprus c-quam exciter here, http://www.ebay.co.uk/itm/322220760379
I will test this tx and offer my results.Paul.
Total posts : 45366With revived AM stereo activity it’s time to wonder about AM stereo receivers.
What is the low down on them? Are they available either from dealers or on-line?
Total posts : 45366I also have the DIP Switch version of this transmitter, not sure how old or new mine is compared to Boardmaker’s. It isn’t a bad unit, sound quality is somewhere between a TH and SSTran. Not bad but my Rangemaster sounds better, that being said the AM Stereo works and does sound quite good. The internal AGC does a good enough job at keeping the audio and modulation where it needs to be. None of these units tune the whole band, the Dip Switch models tune 1024-1750. The pushbutton tunes 1024-1710.
To answer Carl’s question, you can find AM Stereo tuners on eBay quite often. I got my JC Penny MCS AM Stereo tuner for $20 off eBay. I’m unaware of any current manufactures of AM Stereo capable radios, nearly all the ones you will find will be of 80s or very early 90s vintage. Some early HD radios could decode AM stereo, albeit with the channels reversed.
Total posts : 45366Carl,
I am presuming you were asking for new c-quam capable receivers only.
Over at your end of the pond, i assume hd receivers are the only route left for possible new c-quam stereo decoding ?The problem with used c-quam portable receivers, in my experience, are most are faulty due to scratchy potentiometers and switches, as well as dried out/leaked capacitors.
I have bought numerous c-quam receivers, over the last 18 months, and most needed refurbing.
Typical used portable receivers are Sony srf-a100, and the Sony srf-a1 walkman.
Typical used tuners are the Denon tu-680nab, and the Carver tx-11a.
More rare used c-quam receivers are the Sony st-jx220a and Sansui tu-d/tu-s amx variants.
Kevin is your man to talk about a wider list of receivers.
Paul.
Total posts : 45366Getting a stereo AM transmitter on the air is only half of the solution.
Thank you BOARDMAN for the briefing on stereo AM radios.
So what are stereo stations going to do about the receiver problem?
Not only will listeners probably not have AM stereo radios, they’ll need to be convinced to buy one and good luck on that.
Anyway, it’s a worthwhile pursuit. AM stereo should never have died and we are probably the best ones to bring it back.
This may be over-ambitious, but we could buy up AM stereo radios, refurb them, and either give or sell them to potential listeners.
Maybe the secret for a part 15 station is to buy listeners just like another piece of equipment.
Total posts : 45366Yeah Carl, that’s right, AM stereo receivers are a problem here in the US, though old cars and trucks with factory radios can have them, and some HD radios added on C-Quam.
Instead of the whole transmitter, I’d like to see technicians come out with just a plain exciter for Am stereo, that you could apply to any transmitter, commercial or homebrew, so you could retrofit the transmitter you have, you might have spent a lot of money on it, or it gets out well already.
My idea would be the exciter, that also comes with schematics for a one stage final, or higher power transmitter if you can use one in your situation. If you have a transmitter, you could just add it to your unit, with instructions on how to do that.
Looking up outboard stereo exciters in commercial radio, like the unit I saw from Delta, it was a rack unit that takes left and right audio inputs, and bypasses the transmitter’s oscillator with its own, replaces it as the station’s frequency standard.
For example, if you’re on 1190, then the stereo exciter produces that 1190 signal instead, and that signal now contains the phase modulated stereo information (left minus right), and 25 hz pilot tone.
Also coming from the box is left plus right, or mono audio that goes to the station’s main modulator for mono radios. In the exciter, the L+R and L-R audio take separate paths, but are processed together in some ways, tied together, then there’s a time delay adjustment on L+R to account for the small differences in delay of the L-R through the transmitter’s RF section. I’m learning this part right now, but that seems to be it.
The problem I see is that all the AM stereo rigs that have come out in hobbyist circles contain the transmitter, often at low power, and need a linear amplifier, which is more wasteful than a class C or higher stage. In Part 15 it uses up your allowed input power, if you’re lucky, you’ll get 25 milliwatts out.
Total posts : 45366Great active testing BOARDMAKER! Wow, that Cypress transmitter is expensive for 100 milliwatts and a refurbished unit, let’s hope you make a monetized Yutube unpack and use video to make some of that money back 🙂
Ramsey Kits’ AM-100 I think it is, the PLL mono TX has a similar VCO oscillator with a coil, and I didn’t find microphonics as much as modulated RF feedback causing FMing. I could see that being a REALLY big problem in a stereo transmitter, because the feedback would be causing phase modulation too!
How much phase change is required for stereo, isn’t it less than 45 degrees? I’m guessing the phase modulator is based around the NE602?
I see linearity problems in so many AM transmitter circuits, where they just can’t make it to 100 percent either way, especially negative.
Total posts : 45366Nate Crime there is a guy named Dave Schmarder who might be able to solve the problems you have detailed.
Total posts : 45366Thanks for the link to the interesting site, Carl. I wonder how far a box loop like that would transmit? Since it’s a loop, it might get out farther for apartment dwellers like Legacy and Friar Bruce of Dogradio, than a long wire antenna.
See, I’ve tried it on a Ferrite loopstick, long ago and it didn’t work well because apparently the stick absorbs all the power, where an open loop wouldn’t have that core loss, and it’s bigger.
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