Could I get by using a seperate antenna to test for desense? Say leaving the antenna for the receiver through the duplexer and hooking the transmitter up to another antenna, would that work the same to test for desense. I tried to make an iso-tee, did not heave real good luck with it, but then as far as a machinest, I have to luck at that, hihi....
Mathew ----- Original Message ----- From: "Eric Lemmon" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, July 26, 2004 6:09 PM Subject: Re: [Repeater-Builder] Receiver Sensitivity Testing Through Duplexer > Mathew, > > There may be more than one problem to consider. It is wise to check for > desense, but also be aware that some amateur-grade handhelds are > notorious for excessive PL deviation. Alincos are the worst, in my > opinion. My DJ-S11T had 1400 Hz of PL deviation out of the box, when > 400-700 Hz is ideal. When a commercial-grade repeater (MICOR, GE, etc.) > receives an input from a user with excessive PL deviation, the user's > voice may over-deviate the carrier, causing the PL to be clipped. When > this happens on a PL-required repeater, the repeater shuts down on voice > peaks. Of course, this symptom is made much worse when the voice > deviation is too high, as well. One way to check this is to use a > commercial-grade handheld radio to check for the same symptoms. > > To check for desense, you can use an "iso-tee" to inject a low-level > signal into the antenna feedline at the receiver frequency, while > monitoring the receiver audio at 12 dB SINAD with the repeater > disabled. Then enable the repeater so that the transmitter turns on. > The SINAD reading should drop no more than 1 dB. Some service monitors > will change modes when RF is detected, so you may want to use a separate > antenna, instead of the iso-tee, to get the test signal into the > receiver. > > If your repeater is at a site with other transmitters, you may need to > add some bandpass-only (NOT pass/notch) cavities between the duplexer > and the receiver input. As has been noted many times on this list, a > pass/notch or "BpBr" duplexer has almost no bandpass selectivity, and a > nearby transmitter many MHz away can easily cause desense in your > receiver if not filtered out with a dedicated bandpass cavity. > > 73, Eric Lemmon WB6FLY > > w9mwq wrote: > > > > I need a little advice here. I want to test my repeater's sensitivity through the duplexer, while the transmitter is keyed up, into my Cushman Service Monitor. What is the best method of doing this? Do I need an isolator of some sort, or will the service monitor handle both the incoming power and the outgoing signal > > generator? It's a Cushman 6030 by the way. The repeater is working excellent for the most part. The problem that I am having is on weak signals, the audio is being chopped out, almost like the PL deck is shutting down. On the bench, the receiver is at about .25 microvolts sensitivity at 12 dB Sinad. Audio out of the transmitter > > is about 4 kHz wide, and clean at 100 watts. Any suggestions? Handhelds are able to get in from about 4 miles away, mobiles have no troubles at 30 miles away. The antenna is only up at 60' right now, fed with 120' of 7/8" Andrews hardline. But it seems the handhelds are the ones having the problems, and their signal is not really that bad. Help please. > > > > > > Yahoo! Groups Links > > > > > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
