I want to learn on how to build my own SCA-FM generator so when I buy a FM stereo transmitter kit it would be ready to go to start sending RTTY data and SSTV transmissions while playing music on the main station. I am right now having a tough time trying to find a kit and I don't have thousands a dollars to buy one. Actually I want to learn by doing it myself on a part 15 level on how to generate a SCA-FM subcarrier on 67 kHz or 92 kHz to do test transmissions using ham radio software and do some audio testing. I feel everyone should be able to buy and build their own SCA-FM generator and use it for personal reasons and not for making any money. I have been wanting to do this, but there is no way in finding even a simple VLF transmitter circuit, not even Ramsey Electronics is listening, they just keep on putting in the backburner in the archives so I just put it off until it comes back into my mind and it's been happening for a very long time. I have a SCA-1 Ramsey SCA decoder kit that I want to use again for this experiment under part 15 regulations. No fast food restaurant is not going to pick up my station on FM because it's very low powered. Also I want to do this as well, generate my own RDS transmission on my FM station because it looks bland without one. And I feel that Ramsey Electronics should come out with a SCA Encoder Kit next year for existing FM transmitter owners. I hope you can support this and show interest, because I have been wanting to do it for a long time.
Your project is a good one for part 15 development.
Later I will search around, I know I have seen schematic drawings of SCA generators, and a radio engineer I knew in the 1960s when SCA was new built a 1-Watt FM transmitter with an SCA capability.
Here's the way I see it, and this point of view should make doing this simple enough for someone to figure out how to do.
An SCA generator is a hybrid audio/RF/audio device, an actual long wave signal generator with amplitude modulation.
Build a very low power long wave transmitter for 67kHz, add an AM audio input section, treat the output of the generator as audio rather than RF, and mix it with your baseband FM audio into the FM transmitter. Control the output so it reaches the prescribed modulation level on the FM carrier, 10% or whatever it is.
Bingo!
On another thread we are designing a long wave part 15 transmitter, the first two stages of which could probably by adapted to become an SCA generator.
here is a commercial one. schematic is near last page in pdf
http://www.1150wima.com/pages/667westmarket/engineering/manuals/BE%20FC-30.pdf
It has been a very long time since I did subcarrier work but I recall that the SCA for FM broadcast is a narrow band FM signal usually at 67 kHz which can be injected into the modulator stage of the transmitter. There are many IC's which can provide an audio to FM signal at this frequency with the 4046 PLL being one but the VCO linearity may be a factor and another chip may be better suited for this. Some filtering would be needed at the IC output to produce a sine wave subcarrier.
Some of the FM transmitters have a low pass filter for the audio to prevent interference with the stereo pilot signal so this SCA signal would need to be injected after the filter.
These are some preliminary thoughts on this but I don't think such a circuit would be too difficult to put together.
Neil
Problem with 239 FM is it's ridiculously useless power limit already. Most running a 239 setup don't even have the 19 Khz pilot running, and the 38khz sub carrier disabled so that all of the amplifying capability of the transmitter focuses on the main carrier. Injecting sub carriers robs bandwidth and output of the transmitter.
This isn't an issue when running watts. But at nanowatts, it is a very BIG nano problem.
RFB
I wish I knew how to build a long wave transmitter for 67 kHz or 92 kHz, but there is no schematic for it. Thanks for the tips, but where is a kit or schematic when you need one? It's like getting a board with parts but a blank piece of paper.
I checked that manual out, very complicated. I had to look at the schematic and find out which part goes to the IC's. Also some of those parts might be discontinued or not available from distributors. Also I don't know where the kit came from or where to purchase it. We need a something much to the hobbyist level and works just like this one. Where do we find this kit?
A long wave transmitter circuit is even now being developed by members of part15.us, although it's original purpose is for operating in the LW band, it could easily be redrawn for work as an SCA generator.
http://www.kdxradio.com/deepvoice.html
Someone up the way said that SCA modulation is FM. Let's pin that down, because I thought it was AM. I have been wrong before and this may be again.
I believe it's FM, or digital nowadays.
RFB
tech specs per fcc
http://transition.fcc.gov/ftp/Bureaus/Mass_Media/Databases/documents_collection/rules1983subcarrier.pdf
fcc sca page
https://www.fcc.gov/encyclopedia/broadcast-radio-subcarriers-or-subsidiary-communications-authority-sca
there is also something called fmxtra which is a digital modulated fm stereo or fm sca subcarrier that takes place of traditional fm stereo and sca
Please say more about fmxtra.
First someone said it was AM, but no it's FM. So that would make it even more difficult to build, but I don't know how to build it. Since you are making a long wave transmitter, please have some engineer come up with a simple to make SCA encoder.
This is how to do it. It's like a very low powered FM modulator that operates from 50 kHz to 100 kHz or 40 kHz to 110 kHz that is tunable and another circuit that is switchable or both. It has a power button, a input jack and a volume control to control the audio source modulation and it runs on a battery and power supply.
I hope a circuit comes out soon.
I think experimenting with
ANYTHING (well, almost) is fine.
I wouldn't experiment with
plutonium,(har har)).
Anyway, it may lead to something else, too -
that is even more interesting.
That's happened to me. I start to
work on one thing and it erupts
into something else.
I think what you are trying to do is very
hard, but learning is the thing. I have done
many projects that haven't worked, but
what I have learned has been worth MORE.
Bruce, W 60 HZ
Over on ebay is an FM stereo signal generator which has a 67Khz sub carrier generator built in. Don't know if the sub carrier signal can be modulated, but might be something worth playing with anyway.
Hickok 727 FM Stereo Multiplex Generator
RFB
The subject of FM SCA generation is very interesting and in only one day attracted many replies, most of them containing bits and pieces that actually describe what's needed to build such a circuit.
But gccradioscience has come up on the bumper, honking and flashing brights because we're too slow.
"He's trying not to give up", he said, so my reply is....
I'm going to continue following this thread whether anyone gives up or not.
Breath slowly and relax.