> What happened in my case was the loop in the PD-1173
> can was about 8.5 inches long (8.5" down and 8.5" back
> up). It seemed that was way longer as compared to what
> was seen in other bandpass cans. After reading the
> theory page on Repeater-Builder from John Portune W6NBC,
> he says it really doesn't matter the size or shape of
> the loop (as far as the response goes).
Well.... not really. The proper loop length is a big
deal. Too small is really bad news and too large is
really hard to work with. If your cavity depends on
re-entrant energy it would matter a great deal how
big the size and shape of the loop/probe is.
If the loop/probe length was really out of line, you
might not get a good return loss (swr) through the
reactive sections.
> But as you mentioned, the loop length DOES effect
> the jumper length required.
Quite a bit and it's considered a mostly air dilectric
element.
> So after taking a few other bandpass cans apart and
> measuring their loops, I decided to cut the PD loops
> down to 3.5 inches. This allowed the jumpers that
> were the same length as on the duplexer to give a
> good match.
Smart move... and probably the right move.
> In the end, it was a lot of reading, followed by some
> good suggestions from this group (and recognizing the
> need for a network anlyzer).
Open thy wallet.... and hold thy breath
cheers,
skipp
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