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Re Mode J Receive desense problem

The following was received from Richard Limebear some time ago and it works
fine with my IC-821:

"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."

George, W2CID

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