Creating a Weaver type radio demodulator

Algorithm development and general DSP issues

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RRing
Posts: 5
Joined: Sun Jun 07, 2015 5:37 pm

Creating a Weaver type radio demodulator

Post by RRing » Fri Aug 14, 2020 9:55 am

I am trying to see if I can create a single sideband demodulator for my SDR. I have created an AM demodulator, and a phasing type (all pass networks) single side band demodulator that both work great. An alternative to the phasing demodulator is the Weaver type. I have two audio signals in quadrature(90 deg phase shifted) coming into the FV-1. These signals both need to be band limited with low pass filters to a frequency of approximately 2 kHz, then each signal needs to be multiplied(mixed) one with a sine wave of 2Khz( a little less...below the filter knee) and the other signal with a cosine wave of 2 Khz. Then both multiplied signals are summed at the output. The result is rejection of one of the side bands like you would do with a ring modulator. So my issue is creating the sine/cosine wave at that high a frequency(can't use the LFO's?). I have seen reference to audio test generation with the FV-1 but it is not clear to me if this can be done. Is there a simple approach to creating the higher frequency sine/cosine that will work?

Aaron
Posts: 54
Joined: Wed Mar 04, 2015 7:10 pm
Location: Oklahoma

Re: Creating a Weaver type radio demodulator

Post by Aaron » Mon Aug 17, 2020 5:18 am

There is a program called "Battling LFOs" on this page:
http://www.j8268.com/programs.php
It uses a coupled form oscillator to generate a sine and cosine. You can read more about this algo on this paper:
https://ccrma.stanford.edu/~dattorro/Ef ... nPart3.pdf

RRing
Posts: 5
Joined: Sun Jun 07, 2015 5:37 pm

Re: Creating a Weaver type radio demodulator

Post by RRing » Mon Aug 17, 2020 8:52 pm

thanks...yes the LFO frequency is too low ....I need to create sine/cosine in the 2 Khz range but i did see a sine generator program...not exactly sure what is going on in that demo code but I will look at in more detail.

Aaron
Posts: 54
Joined: Wed Mar 04, 2015 7:10 pm
Location: Oklahoma

Re: Creating a Weaver type radio demodulator

Post by Aaron » Tue Aug 18, 2020 6:21 am

These are the equations I use:

s(n+1) = s(n) + fc * c(n)
c(n+1) = c(n) - fc * s(n+1)

fc = 2 * pi * f / R
f = frequency in Hz
R = sample rate in Hz

RRing
Posts: 5
Joined: Sun Jun 07, 2015 5:37 pm

Re: Creating a Weaver type radio demodulator

Post by RRing » Tue Aug 18, 2020 4:58 pm

thanks!
this will be helpful

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