Thanks, Eric. I'm already doing a search for a new
set.
Main problem is - I'm not financing the project, the county
is...and sometimes I'm not at the top of the priorities list.
:-(
I have a set rated for 250W picked out in the Tessco
catalog, but... Not like Christmas and the old Sears "Wish Book", is
it???
BTW - the set I have is from an MSR2000 110W station.
Motorola is notorious for under-rating their equipment, so does anyone know
whether there is there any headroom on these jugs? And if so, how far can
they be expected to "stretch", if at all??
Mark - N9WYS
From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon
Sent: Wednesday, February 08, 2006 9:55 PM
To: [email protected]
Subject: RE: [Repeater-Builder] Duplexer questions
Mark,
The problem with exceeding the power rating of your
duplexer is complex. For starters, the duplexer cans are going to get hot,
and this will cause temperature cycling that may cause "pumping" of the tuning
rod. This will ultimately cause noise and eventual failure of the transmit
cavities. Let's say your duplexer has a 1.5 dB insertion loss, which is
more or less typical for a four-cavity BpBr duplexer. 1.5 dB loss equates
to about 29% of the signal, so about 44 watts will be dissipated in the
duplexer. That may not seem like much, but it quickly builds up. If
you have a six-cavity duplexer, with an insertion loss around 2.2 dB, the power
lost in the duplexer increases to about 60 watts. Of course, the power is
distributed among the two or three cans on the transmit side. The isolator
will suck up a small amount of power in the forward direction if it is properly
tuned.
If I were you, I'd be looking for a duplexer with a power
handling capacity at least 25% higher than your PA rating. Choose
wisely...
73, Eric Lemmon WB6FLY
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