> Re: Need DB4048 Duplexer Info > "larynl2" <lar...@...> wrote: > Hi all I'm working on a 1 mc. split repeater using this > duplexer.
I would recommend you visit the following web page: http://www.ke3ht.org/14703/db-4048.html > Transmitter is a VHF Engineering; output is 1 watt. I'm > using a Mastr II receiver with no preamp. Interconnect > cables are RG142. The VHF Engineering Transmitter is actually a fairly well thought out circuit and when properly tuned is a more than fair performer. The Mastr II Receiver is a legendary good performing circuit so you're off to a great start. > The old VHF Engineering receiver developed problems not > worth fixing, so everything is on the bench for the new > receiver and re-tuning. The original VHF Engineering Receiver really is/was crap when compared to any real commercial Land Mobile Radio Receiver. > Desense was always an issue with this repeater, with 1-3db > pretty normal. 1 watt and a Master II Receiver with a 1 MHz split? wow... > So I decided to re-tune the duplexer. I used a signal > generator and receiver. All ports were either terminated in > 50 ohms or had a 10db pad in series with the generator and > receiver during tuning for minimum signal through the respective > halves. It seems to tune well and predictably. However, > I'm getting 20db+ of desense with the duplexer operating > into a known good dummy load. I can reduce the desense > considerably by *winging it* and tuning the cavities while > the repeater is operating. (Maybe that's the way I should > tune it.......!) So something isn't right. Someone with a Network analyzer or Spectrum Analyzer with a Tracking Generator would save you a lot of time figuring out what is really going on. > I'm not totally convinced that this duplexer wasn't <played > with> at some point, so it is possible that cables in the > harness were mixed up. There is no labeling or other info > on the duplexer, since the metal box that it was in when > new is gone along with the nameplate. So it is not clear > which side is which, and I may have been trying to use it > reversed (although I don't think so). I believe that this > duplexer was originally ordered for 2M, but I could be wrong, > which could account for some troubles. > > So where would I find info on harness cable lengths so I > can check them? Or if someone has one of these working on > 2M and is willing to make some measurements that would be > awesome. And which half of the duplexer is for the high > and low frequencies? > Laryn K8TVZ Start off with the web page I reference above... cheers, s.
