A friend of mine gave me some "surplus" RG-400 from the place he
worked a few years ago. I got sold on the stuff, and with 50-75 feet
of 5 foot pieces, I've been fortunate enough to use it with reckless
abandon for some time :)
On Dec 22, 2007, at 1:27 PM, Paul N1BUG wrote:
> Oops. I forgot to mention double shielded cable for ALL
> interconnects is an absolute MUST, at least with my duplexer - it
> has notches in excess of 120 dB deep after refurbishing. It doesn't
> take much leakage cause problems when you're dealing with notches
> like that.
>
> Paul N1BUG
>
> Paul N1BUG wrote:
> > Jim Brown wrote:
> >> I have found that the main problem in using a talkie
> >> as the receiver for tuning the notch in a duplexer is
> >> the possible leakage of RF between the signal source
> >> directly into the talkie. Most talkies are not
> >> shielded at all, and any leakage will cause you to
> >> tune a combination of the signal through the duplexer
> >> and the direct signal leaking into the talkie.
> >
> > Yes, I had that problem as well. When I built my last 2 meter
> > repeater (a semi-homebrew using custom re-packaged GE modules,
> > mostly) I crystalled the receiver for both the repeater receive and
> > transmit frequencies with a service switch to select the second
> > frequency. I also built a simple op amp DC amplifier sampling second
> > limiter voltage at a metering point in the receiver and use it to
> > drive a signal strength meter on the repeater front panel. Of course
> > my custom chassis is very well shielded. The receiver is peaked for
> > the repeater input frequency, so it isn't as sensitive on the
> > other frequency; but it is good enough to see the depth of my
> > duplexer notches.
> >
> > I use an old (cheap!) Boonton 202E generator as a signal source, and
> > put 3 dB pads on the duplexer ports (and a 50 ohm termination on
> > whatever port is not used at any specific point in the tune up
> > process). The Boonton is surprisingly stable once it has warmed up
> > for a couple of hours.
> >
> > I've had good luck with this simple setup. But adding the signal
> > strength meter to many commercial repeaters (or worse yet mobiles
> > converted to repeater) could be more of a challenge.
> >
> > Paul N1BUG
>
>
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