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
