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YalekThelembine0391
PostPosted: Wed Aug 02, 2023 12:33 pm 
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This was a recent discovery I had found regarding the use of various SDR software and audacity. It turns out you can actually emulate most of the modulations such as FM, AM, LSB, USB, all in one single plugin, without having to actually transmit with any external hardware...The only driver you need being vb audio cable and some other DSP methods.

With the use of a very special set of audacity LISP plugins: https://github.com/tejeez/audacity-sdr you can actually import these as effect plugins into audacity and emulate these same modulation methods.

Now, it isnt just straight forward on the fly. You the user will unfortunately need to make some audio tracks, like a recording or a set of sine waves or whatever...This tutorial will mainly be for FM, but should also apply to some of the other modes as well You will also need a sample rate of at least 48 Khz, but a better recommendation is 192 KHz, and a stereo track if you want this plugin to work:

If you want to generate a low frequency hum/PL tone: Generate->tone->sine wave at a range of 80-250 hz with an amplitude of at least 0.1dB on your stereo track. The reason for such a low amplitude is because FM carriers are extremely powerful even in vb audio's output. Note, I will only be uploading drive links as this forum isnt too friendly with me via the "img" button.

To modulate FM IQ:

Effects->Modulate IQ signal. And use the drop down menu to select FM:
https://drive.google.com/file/d/1YLwrX3 ... sp=sharing

^^I would highly suggest using these parameters if you want a good 12.5 Khz signal. For now this is just a PL tone. Then, click generate.

To view the spectrogram --> go to your track and use the drop down menu and view it as a spectrogram. I would also open up something like HDSDR and read directly from VB audio cable's output (vb cable-> input), and have HDSDR set to VB audio cable (output) for the input soundcard..and have HDSDR's output directed at speakers so you can hear the tone witout feedback...

Also a nicer recommendation is to have HDSDR at 192 KHz along with VB audio cable both ways. This way theres no spectrum offsets and drops...You should also generate some white noist at 0.1 and turn that gain down in your PL tone track...this way it isnt too big...

https://drive.google.com/file/d/1onI1KJ ... sp=sharing

some other proofs of concepts (a 1300 hz sine) including with a POCSAG signal and one of its AFSK bretherens...The AFSK counterpart I used a high pass filter in the audio before modulation, including its pilot 2900 hz sine...

https://drive.google.com/file/d/15MJZ1I ... sp=sharing
https://drive.google.com/file/d/1OCJdHn ... sp=sharing

https://drive.google.com/file/d/16yCJVJ ... sp=sharing
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Rich
PostPosted: Thu Aug 03, 2023 6:55 am 
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Posts: 1997
This is great ! Thanks for posting.
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YalekThelembine0391
PostPosted: Thu Aug 03, 2023 6:07 pm 
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Rich wrote:
This is great ! Thanks for posting.

Yeah!! This mainly is for emulating signals before actually putting them out in the field. I usually like doing that instead of breaking laws. Its a neat alternative.
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YalekThelembine0391
PostPosted: Mon Aug 21, 2023 10:04 pm 
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To prove how easy these steps are, and how powerful SORFMon's POCSAG encoder can be, plus with the use of HDSDR's infinite frequency entering, here's a video I made of (a non transmission on VB audio cable to the speakers), of an example AFSK POCSAG broadcast lasting 8 minutes: The scenario is of a "fictional broadcast" of a 9.5 magnitude earthquake that hits the lakeshore of Southwest MI, causing a tsunami..

NOTE, the video may still be processing as the video is over 8 minutes..so please have patience while it finishes processing...if it doesnt finish just download it...

https://drive.google.com/file/d/1gW2TfY ... sp=sharing
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