Re: [Discuss-gnuradio] frequency shift with multiplier.... something seems to work wrong

[Federico 'Larroca' La Rocca]

Hi Fernando,

You are assuming that the signal you are getting at the receiver is not delayed with respect to the one being sent. You are thus using a cosine signal source with no phase correction. This is not true, since you are using filters, which always delay samples (moreover, you should make sure that both the LPF and the BPF have the same group delay, mostly by using the same transition width). You are thus getting cross-talk between both channels.

You may experiment by manually correcting the phase of the signal source, or by using a PLL (see the WBFM implementation on GNU Radio or gqrx).

best

Federico

2017-04-23 18:47 GMT-03:00 Fernando <address@hidden>:

I'm working on a stereo FM modulator/demodulator, buth channels get mixed, so I'm doing some test and I have found taht this diagram (faulty.grc.png) does not work well. The output of the adder seems fine

Pilot at 19Khz, lower part of the spectrum with tones at 1Khz and 12Khz, and upper part with tones at 38K+-1K and 38K+-12K (as is a power spectrum signs are not show)

But signals R and L show both 1K + 12K tones insted of just 1K tone in one of then and one 12K tone in the other.

I have been testing part of the diagram apart one of the other and I have found that if I only do the add+substract part It work well

And if I only do the add+frequency displacement It work well too .... so I'm puzzled.

Any ideas please?

regards

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