Juan EA5RS wrote
I am a new K3 owner, got my radio a couple of weeks ago.
While measuring CW filter selectivity I noticed microphonics in the receiver.
I set up a -60dBm carrier on 14020 (it is S9+ on Smeter).
Don`t use headphones, use the built-in speaker
Tune RX with 400Hz filter, say 300Hz away from carrier, Smeter is now S2
Now crank up your AF gain or simply hit your radio with your finger.
What I see is the Smeter jump up and the RX audio replicate the mechanical noise you just created.
I did the same with the generator (a N2PK VNA) and the frequency change is not happening there.
It also happens with the 2.8 KHz filter
This sounds to me as the mechanical pressure is frequency modulating the synthesizer and this is demodulated and amplified by the very high slope of the amplitude/frequency transfer function of the
crystal filters. Still, this should not happen in a high quality receiver
I don´t know if this is usual in the K3 or just my radio is defective.
Looking forward to your replies.
73 de Juan EA5RS
Easy for me to test for this as I had just been re-doing the S meter calibration. In my case I used the XG1 as a signal source (so frequency was 7.040) and I'm using a 500Hz filter. After tuning away until the signal is S2 and the pitch quite low I could replicate what you found.
I don't know what that proves, but I don't see it as a problem because the effect was not noticeable with the signal tuned in properly nor am I in the habit of hitting my K3 during operation. It doesn't surprise me that a physical shock causes a change in frequency.
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