Novel filter for sat working
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JOHN - M1BTR
When working the satellites FO-20 and FO-29, the uplink is on 2m and the downlink is on 70cm. If, like my setup, the beams are close together (mine are about 4ft apart) then there can be desensing caused to the 70cm RX when TX on 2mtr. Also it can cause strong 'hash' to be heard on the 70cm downlink, especially when running a Preamp.
This QRM needs to be eliminated as much as possible as it is important to hear ones own downlink to determine the quality of the signal, correct tuning for doppler shift, etc. My simple aerial system doesn't allow the beams to be spaced any further apart so I had thought of buying, or building a cavity type filter for the 70cm RX when a regular satellite contact of mine (Mike KF4FDJ) suggested trying a 2m / 70cm duplexer - just using the 70cm section.
I had a Watson WD-24N which I had never used and tried the idea out. First I changed the pl259 input plug to an "N" type socket then plugged the duplexer into the 70cm feeder just before the signals enter the Preamp. In my case this is in my linear amp in the shack. It worked well, eliminating most problems with less loss than a tighter tuned filter. (Insertion loss stated as 0.2db)
I would not have thought of trying the duplexer without Mike's suggestion, and pass on this idea to any others whose lateral thinking may be as narrow as mine ;-)
JOHN. M1BTR.
M1BTR @ GB7SKG. # 15.GBR.EU
QRV AO-10 FO-20 FO-29