* Ken Arck <[EMAIL PROTECTED]> [2007 Jul 26 09:44 -0500]:
> Hi Nate
>
> Firstly, in the case of your additional bandpass cavity - if cavities are
> properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't make
> one bit of difference. The problem most people have with proper
> cavity/duplexer
> tuning is that they don't maintain a 50 ohm load on ALL ports when they tune
> 'em. So when they're placed into service, the port impedances are different
> and
> the tuning of the cavity/duplexer changes. Which is why you should NEVER EVER
> tune either without at least a 3 dB 50 ohm pad on each of the ports. From your
> description, I'm willing to bet you didn't use pads :-)
No, we didn't. The IFR does have a pad built into its generator output
and the Motorola Spectra mobile is probably fairly close to 50 ohms.
We did check the Celwave cavity this morning using pads and noted no
change in its tuing. Admittedly, the Celwave is a much different
device than the Wacom BpBr.
> My other comment (and in my humble opinion) is that if you're using a properly
> tuned BpBr duplexer on a low power repeater (the 720 is 25 watts, yes?) and
> you
> need additional cavities in the receive side, you've got bigger issue than
> simply needing an additional cavity. You didn't specify what the inteference
> is
> but have you done an intermod study of the site?
The interference is that the repeater is receiving the public safety
transmitter very clearly which has led me to think intermod. This
TKR-720 is running about 40 Watts.
> IMHO, the additional cavity is a waste of time and effort until you identify
> the source of the interference (and made sure your duplexer is first properly
> tuned)
Right now it's the easiest approach to try and be installed by the ham
over there on his schedule. See one of my other posts for the details
of the site.
73, de Nate >>
--
Wireless | Amateur Radio Station N0NB | Successfully Microsoft
Amateur radio exams; ham radio; Linux info @ | free since January 1998.
http://www.qsl.net/n0nb/ | "Debian, the choice of
My Kawasaki KZ-650 SR @ | a GNU generation!"
http://www.networksplus.net/n0nb/ | http://www.debian.org
