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I thank you for the response .I don't usually set the TX cable at one length and it varies at all my sites .most of the sites may be around aprox 1 meter or so
Thank You,
Ian Wells,
Kerinvale Comaudio,
-------Original Message-------
Date: 01/24/06 15:06:34
Subject: RE: [Repeater-Builder] cable length
Ian,
The cable length is more important on the TX side than on the RX side. However, since the impedances of the power amplifier output and of the duplexer TX input are seldom known with any certainty, it is impossible to know in advance what length that jumper cable should be. The TX jumper cable acts as a linear impedance transformer, depending upon its length in relation to the wavelength of the TX carrier. The chances that any random length of cable will result in a perfect match are slim.
The method I use is to make up a cable that fits the installation neatly, and then measure the power going to the antenna from the duplexer with a Bird wattmeter. Then I install an impedance matcher ("Z-matcher") at the output of the PA. If tuning the Z-matcher makes a significant improvement in the forward power, I know that the jumper cable is probably not the ideal length. I now have two choices: I can start experimenting with longer and shorter cables until I find the optimum length, or I can set the Z-matcher for the optimum setting and close up the cabinet, turn out the lights, and head home. Opinions vary greatly on this issue...
73, Eric Lemmon WB6FLY
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Is it nessary to have the correct length coax from the diplexer to the rx and tx or is there a formular that can show the correct length .I am currently using RG223 coax for these links
Thank You,
Ian Wells,
Kerinvale Comaudio,
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