[Elecraft] Harmonics on AMTOR FEC problem

[Len Koppl]

Trying digital modes using Elecraft K2/100 with Kantronics KAM XL and Mac G4
running RDCP+Mac software. I started getting reports from the 40 mtr net
that I check into that my AMTOR FEC signal was sold copy but described as
having harmonics or RFI.

Hi Jack,
I have had this problem running AFSK with a Kenwood TS-440 and a PK-232 TNC.
The problem turned out to be a ground loop.  Do you have multiple grounds
connecting the rig to the TNC?  If so, try lifting one of them so that the
rig and TNC have only one ground wire connecting them.  My final solution
was a 1:1 audio transformer in one of the audio lines to break the second
ground connection.  In retrospect, I probably only needed to lift the ground
wire at the TNC.

Another problem can be a ground loop via the power supply.  Try putting the
TNC on a battery supply to see if that fixes the problem.  When I run fixed
mobile packet (AFSK) with the PK-232 and the IC-706, I have to remember to
unplug the mic audio from the TNC before using the rig for phone.  I do not
have to unplug if the TNC is running from a dedicated battery.  In the
shack, I have had to move various equipment from one power supply to another
to get rid of the problem.  The two meter rig connected to the same TNC as
the HF rig can cause this, and the problem can sometimes be solved by
changing the 2 meter rig to another power supply.

I don't really understand ground loops very well, but I have figured out how
to eliminate them most of the time.  (They are very frustrating and hard to
diagnose because it sounds like RF getting into the AF circuits, so you tend
to apply the wrong solutions...)

73 and hope this helps,
Len, KD�RC  K2 #2239