[Elecraft] Magnetic field sensitivity

[Ron D'Eau Claire]

From: "Vic Rosenthal" <rakefet@rakefet.com>
> When I first built my K2, I put it right next to my antenna rotator
control.  I
> noticed that operating the rotor caused a hum modulation of received and
> transmitted signals, and Wayne (I think) remarked that the VFO and BFO
toroids
> were quite sensitive to magnetic fields.

I can't compare notes with you using a KPA100, Vic, but I know that the
basic K2 is quite sensitive to magnetic fields. When I built mine two years
ago, my first on-air reports were of HUM on my signal  (in spite of my call
sign, that is NOT a desirable condition!).

It turned out that I had plopped my K2 on top of my linear power supply.
They have the same "foot print" and mounting small transceivers on top of
power supplies like that is very common practice in commercial
installations. But it doesn't work for the K2. The magnetic field from the
power transformer was modulating the signal. Actually, it appeared to be
FM - probably the VCO being modulated as you point out.

I understood that a note was going to be added to the instructions to keep
the K2 away from strong magnetic fields such as those set up by power
transformers.

If the souce of the a-c magnetic field that is bothering you is on the side
of the K2 AWAY from the heat sink, your theory about the heat sink
"focussing" the field so that it is even stronger around the K2 circuits may
be right on! AC currents induced in the heat sink could be making the
magnetic field between the source and the heat sink even stronger than
normal..

Ron AC7AC
K2 # 1289