> The problem is "whatever you have" is probably not 50 ohms, so your
pass
> cavity or BpBr duplexer cavity becomes a matching transformer.
I've seen
> some cavities actually appear to have "gain" because by slightly
detuning
> them from the nominal peak one would see if everything was 50 ohms,
they
> matched my test TX to the 50 ohm load on the wattmeter.
Right, but what we're concerned with here is maximum performance in-
system, not maximally matching an arbitrary standard impedance.
A 10 dB/div. log scale on a
> spectrum analyzer doesn't provide enough sensitivity for this
> measurement. However, a 2 dB/div. log scale, or better yet a
linear scale, is good enough.
Have all three, and use them! :)
> Yes, you can tune your RX cans to maximize power transfer into your
> RX. But then what happens to your notches which you've just moved
as well?
Do the notches last.
> Cable lengths will always be an issue if there are any mismatched
ports in
> the system. This is one of the reasons why I encourage use of
isolators on
> repeater TXs. They may not be necessary at non-comm-sites, but if
you
> start having weird duplexer problems (isn't that the title of this
thread),
> they can help solve a multitude of troubles.
Well, I'm ok with that if you're solving a problem that you have, but
I wouldn't stick them in there unless there was a problem that needed
solving, or I had a situation where I could expect one.
> Sounds like a nice piece of test equipment to have around: a 50 dB
> non-directional coupler.
Have two, both hamfest items. One is celwave, and the other is a
bird slug. Spec on the bird slug is -50 at 25-1000 MHz. Seems to be
a pretty rare slug.
> That's pretty darn good for 2 meters. Around here the 2 meter
noise floor is higher than that.
That's with the Daniels receivers, and with the antenna connected, so
we are seeing the effects of whatever crud is out there. SA shows
significant crud up around 160-170 MHz, but adding my Sinclabs
bandpass did not improve the sensitivity at all.
> >I go up today to replace the water-damaged GP-9
didn't happen, hopefully today.
>
> I spent a lot of time looking for a cheap service monitor so I
could have
> some sort of calibrated signal source at my sites, & I'm glad I
found
> one. A little beat up, oddball make with no documentation
whatsoever &
> only does 12.5 kHz steps on UHF (a problem here in 20 kHz SoCal),
but it
> gets the job done.
Old test equipment is WAY better than none.
My spectrum analyzer was current production when I was in high
school. (Tek 7L12) Still works nicely, still accurate though it
hasn't had a formal recal in a while. I almost always make relative
measurements anyway, where "more is better" is really all I need to
know.
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