[Elecraft] K3 Microphonics

[Julian, G4ILO]

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.

-----
Julian, G4ILO. K2 #392  K3 #222.
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

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