[CQ-Contest] Stubs for filtering

[Peter Barron]

Don't forget stubs have to work into YOUR antenna impedance not a perfect 50
Ohm load..So Test with care yes you can set up with a Network Analyzer but
you might be disappointed. Always check with stubs on the antenna you intend
to work on before going maximum smoke. (if the smoke gets out things don't
work so well).

What I did was to course tune the stubs low using a Receiver and a Signal
generator ( I did also check them with a HP8753 Network Analyzer as a common
sense check) However the nulls did shift somewhat sorry I didn't note by how
much.  I then used a signal generator driving the Interfering antenna and
trimmed the stubs on the actual antenna I wanted the null on.  Also don't
coil stubs together you may have to work on one whilst other is running!

Also if you put your own full power into a dummy load outside (at end of
feed line) at the tower and hear significant  signals on any band start
looking at cables and grounds.  Remember 1KW is +60dBm  S9 typically  -70dBm
or less that's 130dBc or a h***of a difference.


Peter
Ve3pn at igs.net