The Motron units implement the "transmitter fingerprinting"
methods developed by K7PF (
). They plot the
frequency changes when a transmitter is keyed. I saw
a demo at a hamfest, and you could generally tell
different models of the same rig apart when looking
at the plots on a scope. (And in many case you could
identify that the plots were from different units of
the same model radio.)
This shouldn't be too difficult to do yourself by
hooking up a triggered sweep scope to the discriminator
output of an FM receiver. The difficult part is trying
to digitize the result, store it for known users, then
automatically record the signature of an interfering
station and compare it against the stored records.
It certainly is not infallible, since there are a couple
ways to confuse the system. (It must detect the
key-up to get a plot.) But it can be useful in many
cases when someone uses the same radio for identified
and non-identified transmissions.
Just like everything else, you want to have a wide range
of tools at your disposal. Fingerprinting is one of
them. Foxhunting is another. Both require practice
to be good at them. It is sometimes amazing how many
repeater problems disappear when a local club starts
holding regular transmitter hunts, even when (as it
should be) no mention is made of interference tracking
in conjunction with the hunts. For more information
or ideas about transmitter hunting try
www.HomingIn.com
