K3 Microphonics

Posted by Juan EA5RS on Oct 11, 2009; 6:45pm
URL: http://elecraft.85.s1.nabble.com/K3-Microphonics-tp3804324.html

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