Joe, the duplexer had been tuned by someone else. It did appear to work ok in another lashup with other equipment. I haven't been back to the test site to try it without the transmitter but it could have been desense as the COR worked. I'll have to get my cohort to try it as he is close to the equipment in fact it's at his QTH. You may have guessed by now that I'm new to this facet of radio. I'm beginning to realize how important this desense topic is. Thanks for the great question you pose. We plan another test tomorrow with the transmitter off.
73 de Morris KI4IUA > -----Original Message----- > From: Repeater-Builder@yahoogroups.com [mailto:Repeater- > buil...@yahoogroups.com] On Behalf Of Joe > Sent: Friday, March 13, 2009 9:39 PM > To: Repeater-Builder@yahoogroups.com > Subject: Re: [Repeater-Builder] SCR-200(A) > > Hello Morris, > > I'm glad to heard the that you got the receiver working! Just one > question, was the test duplexer tuned to the proper frequencies? Was it > desense or just loss of sensitivity when using the duplexer? In other > words, were you able to hear distant signals with the transmitter turned > off? > > 73, Joe, K1ike > > > Morris Dillingham wrote: > > Well, guys, I promised to follow up with the results of my attempt to > repair > > the old Spectrum 1000 with the later model receiver. Thanks to Larry > and > > Joe, I have determined that my receiver is not an SCR200A but probably a > > later model of the SCR-200. I obtained at least three versions of the > > schematic from this series receiver thanks to these two gentlemen. Of > > utmost importance was finding out the transistor part number since my > > schematic was the wrong version. I was able to replace the front RF > amp > > and get the receiver working again. Before doing that, however, I noted > the > > inadequate wiring, IMHO, in the power supply. The SCR-1000 upgraded PS > has > > plenty of safety factor designed in as far as series pass transistors, > etc. > > but the size of the wires was amazingly small. I completely rewired the > > high current circuits to match the rest of the design. I am wondering > if > > during the period of this antique repeater there was a shortage of > copper > > and the price was high. After rewiring, the power output of the > transmitter > > was noticeably increased to about 78 watts while it's specified as a 70 > watt > > PA. I took the repeater to a staging area where we had another duplexer > to > > test it on the air. (The actual installation is in the county jail in a > > jail cell) Distant signals would develop a COR but there was no audio > when > > using the duplexer. When the antenna is directly attached to the > receiver > > with the transmitter on dummy load, it works fine. At this point we > were > > too tired to go further so will get back on it again soon. I suppose > the > > front end may need touching up with that duplexer which has been checked > out > > on another setup. > > Thanks again to Joe, Larry and the list for their excellent help. > > > > 73 de > > Morris KI4IUA > > > > > > > > > > > > ------------------------------------ > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
