Using Audacity to generate radio signals: AM, FM, FM stereo, AM stereo (C-QUAM)

[@juniorsilvabroadcast]

Remember FM Radio needs some form of audio processing to prevent carrier overmod and audio distortion You need some type of loudness leveling. Multiband compression. Dual band final clipping (low frequency should be around - 1to -2db to prevent intermodulation distortion) and overshoot compensated lowpass filtering. Then you can add a stereo generator. Without this basic circuit you will sound awful on air. And not forgetting the pre emphasis circuit before the final clipping.

[@hs-tc]

yep, this tutorial on its own is NOT sufficient; that's why you'd want to use StereoTool or an Optimod (to any viewers reading this, StereoTool is free and does all of this stuff in real-time)

[@henkw1562]

Very nice video and explanation how these signals work. I have a question and i hope you can help me. I like to make a FM stereo audio file ( 1kHz audio) with the 19kHz pilot and 38kHz subcarrier and feed that into a signal generator to test FM tuners. How do i make such a file? Thanks for your help in advance. Best regards Henk

[@hs-tc]

Hey, sorry for taking 2 weeks to come back to you on this. If you're still after this, do this: 1. generate a 1khz tone, at 50% amplitude 2. generate a 19khz tone, at 15% amplitude 3. generate a 39khz tone, at 7.5% amplitude 4. generate a 37khz tone, at 7.5% amplitude feed this into the "composite" input on the stereo decoder, and it should be good.

[@henkw1562]

@@hs-tc Thank you i will test it. No problem for taking your the time.

[@mr-spoon]

huge thanks very helpful

[@official-bartanimationstud5446]

he speedrun the tutorial

[@migueloliveira7103]

13:23 What's the command that you're using here? It's not working for me. "Nyqyist returned the value 9600" message is popping up and the script is not doing anything else. Could you put here the code you used, please?

[@hs-tc]

I think that's what you get if you try to use a stereo track with that command, or, if it's at a sample rate that's different than the project sample rate.

[@migueloliveira7103]

@@hs-tcThen it's very odd. Because I am applying the command to a mono track and the smapling rate is equal to the project. I'll try with another file.

[@migueloliveira7103]

Nop. Still no luck with the FM Modulation. Which version of Nyquist are you using?

[@hs-tc]

@@migueloliveira7103 Interesting. Huh. Okay, I am using whatever Audacity 3 has, and, it should work on any other Audacity fork (works on Saucedacity and Tenacity). Nyquist errors are annoyingly impossible to truobleshoot...

[@TheSpinninHead]

Thank you so much for making this useful video ❤️ I am new to modulation stuff. I see >20KHz used for modulation here. But audible range is

[@hs-tc]

This is for generating radiofrequency signals to be upconverted in frequency and fed out a radio transmitter, rather than being pushed out a speaker if that makes any sense!

[@adriancressy8363]

20khz wide AM radio is fabulous. And that forgotten C-QUAM for AM stereo, sounds just as good as FM stereo with the proper AM stereo receiver. These are still around on eBay

[@EliDowling]

I tried a song with AM by hooking it up to a radio with a wire on the antenna, but I can't pick it up no matter what channel I try. I don't know if I have to amplify the signal or what.

[@hs-tc]

Your radio can only tune down to 550 kHz, but, your soundcard can only really put out frequencies up to 22 kHz or so. You'll need an oscillator and mixer circuit to step up the frequency from the baseband to the RF range.

[@EliDowling]

​@@hs-tc thanks for letting me know. I'll try to get one soon

[@hs-tc]

@@EliDowling You would almost certainly be better to just build an AM transmitter that does all the modulation and signal generation in hardware -- the solution I'm referring to is a VERY heavyweight solution!

[@hs-tc]

@@EliDowling You'd almost definitely want to just use an actual AM modulator/transmitter that generates the signal in hardware, the solution I'm referring to is MUCH more heavyweight and difficult!

[@EliDowling]

​@@hs-tc ok, thanks again.

[@NDLS1026]

How about Kahn ISB?

[@hs-tc]

it's pretty easy to do -- just do two single-sideband operations (and use a filter curve to do that).

[@hg-sx5nk]

That was awesome, thanks! Now, do FM with RDS - j/k 😎

[@hs-tc]

haha! the solution I use for that is to use that GNU Radio fm-rds package, I think it was... but that's more of a real-time solution I suppose

[@rikzakhamami7454]

Slow down dude

[@hs-tc]

The video was long enough, and, I didn't want to keep folks around forever -- use the 0.5x playback speed!