Topband: Modification of the INRAD Roofing Filter Kit
w0jx at yahoo.com
Sun Oct 21 10:32:35 EDT 2007
Paul: Regarding filter failures, I believe there have been a number of them out there. What happens over time is that the resonant center frequency changes over time and inserion loss increases. It is very subtle and one does not notice it until the main RX starts acting like it is deaf. I finally found the problem by using an Elecraft XG-2. Thought I blew out the front end but it turned out to be in the IF.
I had to crank the 9-1 menu setting up to 17 to restore the signal level to S-9. Obtaining a new filter fixed the problem. When installing a mod like this, it is valuable to record your original gain settings and check them from time to time.
Bjorn: The INRAD roofing filter is still a valuable modification. There is a two stage amp following the filter which makes up the regular filter loss and adds a bit of gain. According to W2AGI, it adds too much gain which is why it might be deteriorating the IMD performance. Mike's mod cuts the gain in the two-stage amp back a bit.
73, Dennis W0JX/8 Milan, OH
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