Hi John, Some quick opinion included information...
I would make 100% sure the duplexer notches are properly placed. I would remove the power amplifier and the preamplifier and resolve the repeater operation to the best possible basic level before replacing them back into the system. Adding two band-pass duplexer cavities (bottles) in one-each transmitter and receiver leads before the duplexer would probably help clean things up quite a bit. At least for the testing portion of your repeater "fun". What are the actual numbers of change when you remove the RX Pre-Amplifier and the TX Power Amplifier? Did you say what brand and model receiver you're using? Do you have any other type of receiver you can try? .... and what is the brand/mode and/or type of receiver pre-amplifier you're using? cheers, s. > "John Transue" <[EMAIL PROTECTED]> wrote: > > Skipp, Mike, and others, > > > > A ham club member has a tracking signal generator/spectrum analyzer that > he said has recently been calibrated. He re-tuned the duplexer for me. > Now the receiver hears better than before, but the de-sense has not > changed much. > > > > I have tried the repeater with and without the receiver pre-amp and with > and without the power amplifier. The de-sense changes magnitude as you > might expect, but it is still significant. And without the power > amplifier we are down to only 5 watts, not enough to cover our intended > area. > > > > I am suspecting that the receiver or transmitter is off frequency enough > to be a problem. Actually, the receiver pass band appears to be broad > enough that I don't think receiver frequency can be the problem, but if > the transmitter is off a bit, it could be away from the notches in the > duplexer receive channel. Does this make sense? > > > > I'm not sure what to do next. Any suggestions? > > > > The spec on the duplexer (Motorola T-1504A) is 80 dB of receiver > isolation at transmitter frequency. Also, the minimum separation is > given as 2 MHz while we have 5 MHz. This would seem to give enough > isolation, wouldn't it? Should I be considering six cans giving about > 100 dB of separation? > > > > John > > > > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] On Behalf Of John Transue > Sent: Saturday, July 19, 2008 4:10 PM > To: [email protected] > Subject: RE: [Repeater-Builder] Measuring Desense > > > > Skipp, > > > > We have new commercially made RG-400 cables on both the transmit and > receive side, and we have RG-214 from the tee to the Heliax transmission > line. The new cables could have a fault, of course. > > > > I am going to take a break from this - going to the beach. I'll get back > to it after that, and I'll let you know what happens. > > > > Thanks for all the help. > > > > John > > > > > > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 > Sent: Saturday, July 19, 2008 12:27 PM > To: [email protected] > Subject: Re: [Repeater-Builder] Measuring Desense > > > > > "John Transue" <jtransue@> wrote: > > I made the desense measurements, and I can't believe the > > results. I get about 12 to 14 dB of desense. Is that possible? > > May not all be desense but what the overall effect you experience > is lumped in together in the same "desense" label. > > > I believe that re-tuning the duplexer is the next step. The > > "touch up" a couple weeks ago was not complete. I have installed > > new cables in the cabinet. These are RG 400 so I don't think > > the desense is coming from cable leakage. > > John > > Never say never if the wrong cables are anywhere close to each > other. Few if any cables regardless of type are "100% sin free" > including hard-line. Ensure you have as much practical physical > cable spacing as possible. It doesn't take much stray RF energy > to really rain on your receiver parade. > > s. > > > __________ NOD32 3192 (20080616) Information __________ > > This message was checked by NOD32 antivirus system. > http://www.eset. <http://www.eset.com> com > > > > __________ NOD32 3192 (20080616) Information __________ > > This message was checked by NOD32 antivirus system. > http://www.eset.com >
