It's time for a reminder: Guessing what a particular RFI manifestation
might be accomplishes NOTHING.
If your receiver is listening on a particular frequency and is being
impacted by some sort of interference all the speculation as to what it
might be won't find the source and fix it. You must equip yourself with a
receiver you can carry that listens on the affected ( and higher )
frequencies. The receiver must have some sort of signal strength indicator.
An RF Gain control or attenuator is helpful.
Finding lower frequency sources is more challenging because they tend to
propagate further and can be a mile or more away. Higher frequency sources
are easier to locate because it may be possible to use a directional
antenna.
Ideally, the portable receiving system can be configured to show a
mid-scale signal strength on the indicator when you start. An expanding
circle or expanding square search from your location should show changes in
signal strength. As the signal strength trends become clear, you keep
moving toward the source. It is vital to control the signal level
indication at or near mid-scale. As you get closer to the source you will
need to attenuate the input to the receiver ( reduce RF Gain, lower or
shrink the antenna, increase the attenuator level...). You must be able to
observe changes in signal strength.
You should be able to pinpoint the source to a pole or a house or a
building. Your next move will be determined by the structure you reach.
CAUTION: Be absolutely certain you have found the correct structure before
you knock on anyone's door or make a call.
If this kind of searching (called "DFing" or direction finding) is beyond
your capability, get local help. Take advantage of your local utility's
RFI/TVI Investigator. Enlist the aid of the top Bunny/Fox Hunter in the
local ham community. It is VITAL that you are absolutely, unquestionably
certain of the source before you take any steps to mitigate it.
I use 2 tools to great advantage in my professional work as a utility RFI
investigator: Tecsun PL660 and the National RF HFDF Vector Gun kit. The
Tecsun portable AM/FM/SW/Airband radio covers the spectrum nicely giving me
the ability to listen for just about anything and zero in on the structure
by walking. The National RF kit allows me to DF down to 3.5 MHz with enough
accuracy to get close enough to pinpoint the structure.
There is only one way to zero in on a interference source: Equip yourself
with the right tools and go find it. It could be in your own home or it
could be within a mile or so. Take these steps and you won't have to
guess.
73,
Frank N. Haas KB4T
Utility RFI Investigator
Florida
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