ADAU 1701 4 CHANNEL SSB TRANSRECIVER
Hello everyone,
I have to implement a 4-channel SSB communication system with ADAU1701.
I am obliged to use the 96.000 sample rate because otherwise I cannot make the modulation at 31.250 and at 32.768, consequently the instructions are reduced to 512.
The DSP does many things and therefore the instructions are precious, I did the part of the modulator that transmits on 4 different channels and I attach the project, clearly in reality the microphone input has its own equalization, compression, etc. as well as then the audio output, not shown in the attached project for simplicity
The transmitter modulates the 4 channels correctly, my problem is how to carry out the reverse operation, then demodulate the 4 different channels with very few instructions.
I tried to apply an SSB signal instead of a microphone to try to demodulate it, but with poor results.
Surely to demodulate you have to change the configuration of the Hilbert Transform, using filters I could do demodulation, the problem is the limited number of instructions, I don't have enough.
Someone can suggest a solution using the same modulator configuration also to demodulate the 4 channels.
Thankstest_modulatore_TX.zip
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Hello piero,
As you're aware, you can recover audio with only a multiplier as shown below. This works for any of the four channels. Likely, though, you need to select and receive just one of four channels being simultaneously transmitted -- this is far more difficult.
The first difficulty I see is that the two carriers are so close in frequency that even if you limit the voice BW to a barely intelligible 1.5 KHz, CH2 (32768 LSB) and CH3 (32150 USB) appear to run into each other. (see below). Most likely I don't understand the theory and/or your application.
Best regards,
Bob
why not just use two of the 1701 chips or boards? they are cheap enough. I was trying to do it all with one and decided to move to two or more. I use the Sure Wondom boards and I think the 1701s are still less than $22 per and they come with 4 pots and a nice audio interface adapter for cheap as well. They also have a nice volume and other rotary controls available as well as cheap amps. I think they started in the gaming industry for pinball and other standalone machines. Not involved with them directly, but their boards show up everywhere.
Also, I don't understand why you need such a high sample rate unless you are sending a data format I'm not familiar with. I would think four channels at 4K you could easily squeeze into 32K or with guard bands 48k.
Hi Bob sorry for the delay in answering but I was out of Italy for work and I couldn't read the forum.
The problem is that there are communicators on the market who adopt these frequencies and we must adapt to be able to communicate also with what exists.
The frequencies are very close and so there are many problems, I didn't choose the frequencies, these are used for a long time.
The channels are transmitted one at a time and the part that manages the transmission works perfectly.
If I transmit on channel 1 I am obliged to receive on channel 1 if I transmit on channel 2 I receive on channel 2 etc.
I will see how to minimize interference between channels.
Thanks for your help
Piero
Hi cncjerry,
thanks for the advice, but I am obliged to use ADAU1701 because besides carrying out the SSB modulation I have to do many other operations.
Piero
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