Another AM Broadcast Interference Story

Bill,Pete

Another great solder smoke podcast today.  I especially liked the detail
of you using the S-meter to check on the local broadcast station, and
the better reception you had on 160 with a resonant antenna.  Before I
retired I had spent over 25 years as a field service tech working on
neurological instrumentation.  One of the test our instruments performed
was called an Electro-Myography. Part of this test involved a needle
electrode being inserted into a muscle.  This was fed to an
instrumentation amplifier connected to a computer that processed the
output of the amplifier.  The signal from the amplifier was also fed to
a speaker so you could also hear the response of the muscle fibers
activating as you flexed the muscle.  One of my customers called and
said that quite often when he inserted the needle electrode, he heard
music  instead.
I made a trip to his office and  using a field strength meter, I could
see the modulation peaks on the FSM.  But only in one location against
the wall in the exam room.  I at first thought it might be from a
speaker cable for their intercom / background music system in the wall. 
But there was no wires near that location , and it was an outside
wall.  I went outside with the FSM and found that the signal was coming
from the down-spout for the rain gutter. Apparently the gutter was
resonant at the frequency of the local AM station and the received
signal was being radiated through the wall and picked up by the amplifier.
I quickly got the set of jumper cables out of my van and connected the
down-spout to a near by water faucet, the signal went away. After a
quick trip to the local Home-Despot and picking up some heavy copper
wire and a ground clamp for the water pipe I was able to fix this
problem.  It is amazing how broadcast interference can show up in so
many places.

DuWayne