In order to do a meaningful calculation, I would have to know the type of
dielectric in the coax to determine the velocity factor. The VF will be
less than one.
73
Glenn
WB4UIV
At 07:36 PM 10/01/04, Tim S. 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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>
>Yahoo! Groups Links
>
>
>
>
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