de W5DK wrote:
> Not to hijack the thread, but a dummy load is NOT always a perfect
> test to eliminate the equipment. I think it’s a good start though.
>
>
>
> I just solved a situation where I had 15 db desense into a 600ft
> feedline / antenna and ZERO desense into a dummy load. This was using
> a sample slug ( same function as iso tee)in my bird 43 where the feed
> line attached to the cabinet. My assumption that the complete
> repeater, duplexers, isolator and cables were fine into a dummy load
> led me to look at the hardline and antenna and prepare for paying for
> a climb. Before we could properly test the feedline and antenna, the
> mastr II PA failed. (VHF) after replacing the amp, the 15 db desense
> problem was gone. So the failing amp liked the dummy load better than
> 600ft of 50ohm feedline and antenna . Or some product from the amp
> excited the feedline /antenna to create something on our input. The
> low level products on our input creating the desense were not visible
> when I had looked at the spectral output of the amp before it failed.
It sounds to me like the PA wasn't aligned properly. Or the duplexer is
not aligned properly. Most, but not all, MastrII PA's have an output
filter section that is tricky to align correctly.
There is lots of info on it on the repeater-builder web site.
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