Re: #ubitx-help Strong Audio Tones in and outside audio receive passband #ubitx-help

Jerry Gaffke

So, moving the Nano 8" away did away with tones in the crystal filter passband, 
which would be the ones of most concern to folks here in the forum
But you still see tones coming through the demodulator, up around 13khz. 

Can you give some idea of how strong these 13khz tones are?
I assume they are relatively weak.

You said that a finger on the 16mhz crystal does not affect these tones.
Did a finger on the 16mhz crystal affect the the tones you heard within the passband
back before the 8" move?

There's all sorts of weird things that can happen around mixers.
Always have some unwanted products that come out the IF port.
We have a filter there (45mhz or 12mhz) to only select the signal of interest,
those other signals are not getting terminated and so reflect back into the mixer
to mix again, creating all sorts of unexpected havoc.
Could be this 13khz stuff has nothing to do with the Nano.


On Sun, Feb 4, 2018 at 09:19 am, Jerry Gaffke wrote:
Ah, very nice that you were able to do all of this, and document it so well.
See my comments inline with your original text below

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