On Thursday 30 September 2004 02:16 am, Tim S. wrote:
> However, I put the service monitor on the PA output and
> read 42 watts. Hooked the cabling up to the duplexer and
> then checked the output of the duplexer and only read 22
> watts. That's like a -2.8db loss.
What is the SWR looking into the duplexer? Have you tried
different length cables from the transmitter to the
duplexer and looked to see if the power coming out of the
duplexer changes? When hooked to the duplexer, your PA may
not be putting out 42 watts. I keep a selection of various
length cables (in increments of 1/8 wavelength) at the
repeater site for investigating stuff like this.
> When I tuned the replacement I double checked all the
> peaks locked them down then did the rejects. So I am
> pretty confident the duplexer is set right.
Even a properly tuned duplexer can upset a PA.
> 1. Can something in the original duplexer go bad
> internally to cause the desense? Or must my tuning be
> suspect?
Any number of things could go wrong with a duplexer... bad
cavity interconnect cables, internal corrosion, hidden
lightning damage...
> 2. Think I need to worry about the -2.8 db power loss?
I would investigate to find out why you're seeing these
numbers. If you're really losing 2.8 dB in the duplexer,
something isn't right. Try some different cable lengths
between transmitter and duplexer to see if it has an
effect. Note: placing a directional coupler between the
transmitter and duplexer to measure power there may or may
not work like you want... you should simultaneously measure
power out of the duplexer, since adding a coupler after the
PA changes the line length and hence may significantly
change the load the PA sees! Made that mistake once or
twice....
Let us know what you find.
Paul
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