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Author Topic: Digital Communications using Sound Card  (Read 2746 times)
K6YOP
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Posts: 1




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« on: January 29, 2014, 02:25:54 PM »

Greetings DE K6YOP from San Jose California.

I am experimenting with digital communications over Sound Cards.  On one side I have a Modulator that modulates various digital communication schemes via the sound card and on the other side (receiver) I have the same setup with a De-modulator.   This is at the moment a Half-Duplex system and I am able to achieve 100 Kbps using a QAM64 Modem on both sides of the system and a program called J-QAM (http://homepages.paradise.net.nz/peterfr2/QAM.htm).

I am wondering if anyone can recommend other Software defined Modems with different digital modes that use the sound-card? 
In specific I am looking for Maximum utilization of the 20KHz bandwidth available on the Sound Card to achieve a maximum possible Bit Rate in optimal receiving conditions.
In Short, I would like to break the 100 Kbps barrier (if Possible).

Thanks
Yaron (K6YOP)
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G7MRV
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« Reply #1 on: February 19, 2014, 10:45:55 PM »

If your using a soundcard with a max 20kHz B/W, how do you propose transfering data beyond that bandwidth? That will surely be your limiting factor.

You could go to greater than 64QAM, but you will start to need expensive profesional modem chips.

In broadcasting, we increase the data rate by not only increasing the modulation vector points (ie BPSK>QPSK>16QAM>32QAM>64QAM) but also by increasing the number of carriers transmitted. In DVB-T (the system I work on) we use 64QAM over 8k carriers (8,000 carriers!) within an 8MHz RF bandwidth

To the best of my knowledge, to reach 100kbps, you will need >100kHz bandwidth, so if intending to stay with soundcards will need a very expensive one.

By moving away from soundcards to USB data transfer, you can get some 3Mbps to play with. But then your problem will be where to use this? The only ham bands where you could run that kind of necessary bandwidth will be in the microwave regions.

The big question though is why? Huh
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KB1NXE
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Posts: 311




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« Reply #2 on: February 21, 2014, 12:01:08 PM »

Do some research into Hartley's Law.
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