Using the ADAU1700/1701 DSP for Radio Communications
We are currently working on a multimode radio transceiver and one of the functions we wanted to add was DSP primarily for audio signal processing on SSB receive. This in reality is a low intensity application and the frequency range we would be concentrating on lies between 300 Hz and 3.5 Khz. Are there any codecs/plug ins available for Sigma Studio which are biassed or more suitable for this type of application, and has anyone looked at using or used these DSP's for this type of application?
Any information would be of great help at this stage, no matter how small it may seem.
Thanking you in advance, John
fm
single_sideband
radio_communication
am
ssb
Hello John,
Although there's no "RF specific" algorithms for SigmaDSPs, others have built SSB projects with the ADAU1701. For example, the schematic shown below performs basic SSB modulation and demodulation. It operates at a IF frequency of 12KHz while running at the -1701's standard sample rate of 48KHz.
Quadrature VCO and Hilbert Transform blocks build a Hartley phase-shift SSB modulator. Flipping the phases around produces LSB or USB output. The receive chain provides for envelope detection or product detection with a simple beat-frequency oscillator (BFO) adjustment to clarify the received audio. Although not shown here, a software phase-locked loop is also possible. This would allow for synchronous AM detection.
This project runs on the standard ADAU1701MINIZ evaluation board. With a voice podcast input, the envelope detector outputs the characteristic "Donald Duck" sound of SSB. Switch to the product detector and adjust the eval board's potentiometer for clear speech. As shown the project uses 301 instructions out of the max of about 1000 at a sample rate of 48KHz. If needed you could run at 96KHz to accommodate a higher IF, but that cuts your maximum instructions in half.
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Thank you,
EZ Admin
Is the flow chart still available? I'm doing a SSB modulator and demodulator with voice band 300 - 3600 Hz and need a Hilbert or quadrature oscillator. Thanks
Hi AeroS,
I just noticed your question here while researching another question on a newer thread. The project described above is attached below. Because the IF is only 12 KHz, it operates at 48 K. You can easily modify it to do 96K if needed*, with a few instructions to spare. The project file is attached below.
SSB-Modulator-Demod.dspproj
* For how to change the sample rate, see this article:
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