[Elecraft] FM Broadcast Station Interference

[Stuart Rohre]

Tom,
To have this RFI without an antenna, it must be getting into the rig from
your shack having some resonant structure that tunes close enough to the FM
station  to act as a strong re-radiator, (gain antenna).  Check your wiring
lengths, phone wires, anything that might bring the signal into your
operating position.  Make a tuned wavemeter for this FM channel, and move it
around the wiring, metal of desks, bench, etc. and see what is hot with RF
at that frequency.  You may find that you can "filter" the RFI by relocating
the operating position of the K2, or take out some overly long wiring, or
put ferrite beads on the phone line coming into the shack, if it is the
source of high RF of the FM station.  If it is reradiating off the AC
wiring, in the room, you might get a brute force AC filter for the offending
circuit.  Sometimes even by pass ceramic caps of 0.005 mf across the outlet
plug might derail the RFI.  In the "old" days, hams often made up a standard
AC plug with a 0.005 across line and neutral, (be sure it is 1000 volt rated
disc ceramic,) and used that to bypass RF off the AC line.

Make sure your DC supply leads even from a battery are not exactly resonant
at the FM channel, and are twisted pair, or even better shielded twisted
pair.  Could be as simple as the length of that DC cord, or the mike cord,
key cord, or headphones cord being resonant.  RF ferrite beads might work on
all.  But, sniff out the RF carrying culprit first.  A scope is nice for
this, as well, as you can use a coax and a two turn or so sniffer loop to
the scope and see where that FM signals is strongest.

72,
and Good Luck,
Stuart K5KVH