Well Tim, that is going to be real close to 3/4 wave length at your
freq. assuming a .66 prop facter like RG214. Still It would never
hurt to have a matching device between the Tx and the duplexer.
Normally it would be in the form of a pi network for the band in
question. They are easy to build normally a home made inductor and a
pair of veriable caps. or you can lay out 50 to 100 bucks for a
commertial one.
73
--- In Repeater-Builder@yahoogroups.com, "Tim S." <[EMAIL PROTECTED]>
wrote:
> Thanks to all the help here and repeater-builder.com I got it
figured out.
>
> Quite interesting actually.
>
> I verified the input to the duplexer had 42 watts by using a
coupler on the
> duplexer input cable and hooking it up to my service monitor.
>
> And hooked it all back up and I had 42 watts into the service
monitor
> measuring the duplexer output.
>
> So 42 watts in and 22 watts out was -2.8 db loss.
>
> Next I checked the antenna reflected power with a bird. Bare with
me here
> because the bird readings are vastly different then my recently
calibrated
> monitor.
>
> The ant showed 38 out and 1/2 watt back with the bird. Pretty
good.
>
> So I checked the input to the duplexer. 65 watts out 12 back.
Not good. (I
> guess) I say I guess here because changing the length of the
duplexer input
> cable seems to affect it.
>
> I decided to check the duplexer tuning once again and pulled the
unit.
> Retuned the plungers all the way up and down and could not find a
better
> peak. Reset the notches and reinstalled.
>
> Same kind of readings as before.
>
> Then I tried a new cable from the TX to the duplexer input that I
had. It
> just happened to be about 3 inches longer than the original.
>
> That gave me on the bird 65 out and 1 back on the antenna.
>
> The service monitor showed 32.5 watts out of the duplexer.
Reverified the
> 42w into the duplexer on the new cable.
>
> For a total insertion loss of -1.1 db.
>
> Also rechecked the densense and could not measure any.
>
> Now for a homework assignment. The original *bad* cable is 24
inches long.
> And the TX freq is 483.0875Mhz. So what wavelength would that be
that
> caused the problem. And I assume it is the original cable when
the repeater
> was installed 25+ years ago. Was it always wrong or did it not
effect the
> original duplexer the same?...
>
> Thanks again!
>
> -Tim
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