[Elecraft] K2 50/60Hz PLL Modulation

[Stewart Baker]

The problem of a power transformer close to a K2 such as to cause problems=
 on 
SSB has oft been reported. What I have not seen so far, is, that because it=
 is 
the PLL  that is affected the problem can also be observed on receive.

Instead of transmitting a "gungy" signal, asking for reports,  moving the=
 PSU or 
K2 around and repeating the process, I used the following procedure on=
 receive:-

I ran SpectroGram with my soundcard connected to the K2 loudspeaker socket.
A strong unmodulated carrier (XG1 set to 50uV) was applied to the ANT=
 input.

It is necessary to get the smallest  frequency resolution (5.4Hz) on=
 SpectroGram 
so set the Scan Input (F3) to these settings :-

Sample Rate 11kHz
Resolution 16bits
Scale 60dB
Freq Scale Linear
FFT Size 2048
Average 70

 Using either the SSB or CW filters tune in the signal until an audio signal=
 of 
800Hz to 1kHz is obtained, and adjust the displayed signal amplitude to=
 around 
0dB. The noise floor in the filter is approx -60dB.

Any modulation of the K2 PLL will now appear as sidebands to the main=
 signal.
They will be spaced at either 50Hz (Europe) or 60Hz. If the problem is=
 intense 
there may be harmonics. Switch PSU's On/Off to confirm (Not the K2 one !)

A small homebrew PSU in a diecast box placed 12in away from my K2 gave=
 sidebands 
of -40dB. I dread to think what the field from a high power linear amplifier=
 
could produce.

D.C (Direct conversion) receivers I have built have shown a greater immunity=
 to 
Electromagnetic induction than the K2. While this measurement technique=
 works in 
helping move things around in the shack, a permanent fix would be most=
 welcome.

73

Stewart G3RXQ