[Repeater-Builder] Re: Need DB4048 Duplexer Info
larynl2 lar...@... wrote: Thanx Paul, who responded directly, Randy, and Skipp. That puts me onto some things to check. So far the harness looks to be correct, with proper length jumpers made of RG9/B. I looked at all of the loops and they are also in good shape and correct size. Next I'll check each cavity individually on their respective notch frequencies. And maybe I should check all elements of the harness with a megger to find lightning damage/carbon tracks. Yeah, 1 watt and desense so bad it's not worth measuring -- something rather serious... Laryn K8TVZ You might try using only two of the cavities in a simple dual cavity duplexer test situation. I suspect what might quickly be labeled desense is actually part of or sourced to another problem. Regardless of the label one small iceberg should not sink this new fancy Titanic Ship. cheers, s.
[Repeater-Builder] Re: Need DB4048 Duplexer Info
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.
[Repeater-Builder] Re: Need DB4048 Duplexer Info
Thanx Paul, who responded directly, Randy, and Skipp. That puts me onto some things to check. So far the harness looks to be correct, with proper length jumpers made of RG9/B. I looked at all of the loops and they are also in good shape and correct size. Next I'll check each cavity individually on their respective notch frequencies. And maybe I should check all elements of the harness with a megger to find lightning damage/carbon tracks. Yeah, 1 watt and desense so bad it's not worth measuring -- something rather serious... Laryn K8TVZ
[Repeater-Builder] Re: Need DB4048 Duplexer Info
Larry did you try RB site. Try this link http://www.repeater-builder.com/db/pdfs/db-4048.pdf Randy --- In Repeater-Builder@yahoogroups.com, larynl2 lar...@... wrote: Hi all I'm working on a 1 mc. split repeater using this duplexer. Transmitter is a VHF Engineering; output is 1 watt. I'm using a Mastr II receiver with no preamp. Interconnect cables are RG142. The old VHF Engineering receiver developed problems not worth fixing, so everything is on the bench for the new receiver and re-tuning. Desense was always an issue with this repeater, with 1-3db pretty normal. 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. 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
