There is no way you can tune a duplexer with a power meter or swr meter. They are not sensitive enough to see the low level signals even if your signal source is a good size transmitter.
You can use a receiver tuned to the frequency you are trying to notch out. Your signal source then should be a signal generator where you can vary the signal level as you tune things. If you use an HT as the receiver be sure to check your test setup FIRST to see that there is no leakage of the signal generator into the HT receiver by other than the antenna jack. You can do this by hooking up the signal generator to the duplexer and cranking up the generator with the HT cable unhooked and see if you can hear the generator. If you can then the HT will not work for a signal detector to tune the duplexer as the leakage signal will interfere with the desired path and give you false readings. You need to have the 3rd port connected to a 50 ohm load on the duplexer when tuning. Is there a separate notch tuning control and a pass tuning control on each cavity of the duplexer? How far are you trying to move the duplexer from its design frequency? If it is a mobile type duplexer then it will be a notch type duplexer and the main cavity tuning rods will be to tune the notch. With this type of duplexer it is also very important to have the high and low frequencies configured properly. If you are trying to move this type of duplexer a long ways from its design frequency it will not work properly because even though it is a notch only duplexer and doesn't exhibit any pass band characteristics there is still a pass side on the notch. The other side of the notch will have higher attenuation. This is usually determined by fixed capacitors on the loop inside the cavities. 73 Gary K4FMX > -----Original Message----- > From: [email protected] [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of Chris > Sent: Friday, March 02, 2007 6:39 AM > To: [email protected] > Subject: [Repeater-Builder] repeater problems, duplexer etc. > > Picked up a vertex VXR 7000, and a Celwave 6 cavity duplexer. (VHF) > > Using Celwave pd-220 3a, with 25 feet lmr. > > We have spent hours tuning the duplexer, and find that it makes the > system deaf. 1 watt out gives 10 miles coverage simplex, and when > using dual antennas with the 3+ mhz bandspread the repeater works, > but since the antennas are in line with each other the results are > not good. > > Using an HT to generate and notch the signals, (as well as a power > meter and a swr meter) all looks good until hooked up and its deaf. A > user a half mile away can barely hold the repeater on an ht at 5 > watts. > > I fully understand that there is attenuation inherent in duplexers, > but this is way too much. freq pair is 4 mhz split, antenna system > and cabling is excellent, rx and tx on the repeater is great, > duplexer is in excellent shape. > > Anyone have any ideas? Are our crude methods of tuning the duplexer > too crude? we tune the high to pass the high and notch the low (and > vice versa on low side) but the duplexer seems to attenuate much > more than expected. > > Thanks in Advance > > > > > > > Yahoo! Groups Links > > >
