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Re: Receiver desense problem



George Hoffman writes:

> My 146 Mhz transmitter at 5 watts or more is heard in my 435 receiver while
> accessing the satellites.
snip
> Are filters commonly used to get around the problem? 
> If so can anyone recommend one that worked for them?

First thing to try is an open-circuit stub filter; all it costs is a piece 
of (cheap) feedline and a T-connector.

T-off the 70cm feedline, as close to the 70cm rig as convenient, with a 
quarter-wave of coaxial cable. Formula for the cable length is about 
2000/frequency (in MHz) but cut it longer by a couple of inches.

To adjust: key up the 2m tx and listen to its third harmonic (or other
product) on 70cm. Then snip short pieces off the stub (say 1/8 inch at a 
time); the 70cm signal strength will decrease. Keep snipping until the 
signal strength on 70cm starts to increase; then stop and insulate the 
cut end. Finished. The stub will not affect the tx side of the 70cm rig.

If the interfering signal is still significant then there may be a 70cm
content coming out of the 2m tx. So repeat the exercise on the 2m feedline
with a stub cut for 70cm.

73
Richard W L Limebear G3RWL
g3rwl@amsat.org
FOC # 1188

          So many beautiful girls ..... (sob) so little time



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