A quarter-wave stub of coax won't have enough Q to attenuate the 444.6
signal without also degrading the 446.x signals as well. A high-Q
pass/reject cavity is the way to go. The bandpass characteristics of a
typical pass/reject cavity should allow both 446.7125 and 446.600 to pass
with near-equal attenuation as they are close in frequency, while still
being able to knock down the 444.6 signal about 40 dB or more depending on
loop settings.
Before going out and spending money, measure how strong the 444.6 sig is at
your 446.x receivers. That will tell you how much rejection you really
need. If your desired signals are strong, you might only need to knock down
the 444.6 to maybe -20 dBm. If your 444.6 sigs are marginal, it may need to
be down below -30 dBm, but probably not more than -40 dBm for your MVP's.
I'm assming you're not using a preamp, for if you are, it's probably only
exacerbating the problem.
You could try using filter sections from a duplexer to do this, but most UHF
duplexers are designed for a 5 MHz split, so you may not be able to get the
notch close enough to the pass (about 2 MHz) without incurring high
insertion loss at the pass frequencies. But your paths have enough margin,
maybe you can get away with it.
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Chuck Kraly
> Sent: Thursday, March 06, 2008 9:04 AM
> To: Repeater-Builder@yahoogroups.com
> Subject: Re: [Repeater-Builder] 440 de-sense
>
> how about trying a 1/4 wave stub tuned to his freq on your
> rcv line? That is IF it is coming in there. or is it coming
> in thru the wiring?
> Chuck K0XM
>
>
> On Thu, Mar 6, 2008 at 7:57 AM, wb8art <[EMAIL PROTECTED]
> <mailto:[EMAIL PROTECTED]> > wrote:
>
>
> Hi, I have a slight problem with a 444.6 output
> repeater and looking
> for the best and low cost approach to fix. We have
> just moved to the
> site and the owner has the 440 repeater. The ants are
> all at the same
> height and hence we only have a small amount of horiz
> separation. We
> can't change this as on cell tower as part of the
> owners deal for the
> site. So what it is, is it. We link the the site on
> 446.7125 and
> 446.60, and his repeater at 10 watts, is DE-sensing our
> receivers
> which are GE MVP's. Guess looking to the experts on best viable
> solution. I have been able to try anything yet but
> have considered a
> mobile duplexer as an option.
>
> Thanks Randy
