Ok, looks like I need to get the Iso-tee made then. Mathew
----- Original Message ----- From: "Chuck Kelsey" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, July 26, 2004 7:25 PM Subject: Re: [Repeater-Builder] Receiver Sensitivity Testing Through Duplexer > No. > > > > ----- Original Message ----- > From: "Mathew Quaife" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Monday, July 26, 2004 10:17 PM > Subject: Re: [Repeater-Builder] Receiver Sensitivity Testing Through > Duplexer > > > > 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 > > > > > > > > > > > > > > > > > > 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/
