Welcome to the wonderful world of duplexers. When I first started messing with repeaters I used nothing more than a signal generator with attenuator and an ht with a bar graph signal strength meter. That and a dummy load is the minimum you really need to do a decent job. I replaced a 2 meter receiver with a hotter receiver one time and experienced reduced rx coverage much as you described, I traced it down to the cable between the transmitter and duplexer. This was causing the transmitter to see some reflected power looking into the duplexer. As per Wacom manual I started adding a couple inches at a time until the reflected power went away. I ended up having to add about six inches to what I had. The hamtronics receiver wasn't bothered by the resulting effects from the mismatched transmitter load but the Spectrum was. My duplexers were tuned at the factory I suppose on a network analyzer that is supposed result in a perfect 50 ohm input, trouble is my transmitter was not a perfect match hence the reflected power. By adding length to the cable I was making a transformer that made the receiver happy. This may not have anything to do with your problem at all. You need to check your antenna match first then see if your transmitter is seeing the same SWR when the duplexer is in line it should be the same. You need a way of quickly turning the transmitter on and off while listening to a weak signal. If the signal improves when the transmitter is off then you are experiencing de-sense. This could be caused by many things. Bad cables or connectors or feed line or duplexer or too much power or spurious transmitter or poor receiver or... the list goes on. you need to give us a rundown on what your system consists of - what antenna feed line connectors cables transmitter and receiver are you using.
tom ----- Original Message ----- From: Michael Ryan To: [email protected] Sent: 7/29/2008 11:36:32 PM Subject: [Repeater-Builder] Curious Situation Rbers, I posted a note very early this week about my looking for a someplace to get a 220 duplexer tuned in the TAMPA area. Having not much luck I contacted a local MOTOROLA shop and paid $95 for the service. The receipt returned with the cans indicates that the specifications published by WACOM are very close. Having tuned these merely to incoming signals before, peaking them while the repeater is still in a testing mode, seemed to return decent results but the tune-up was thought to be a better idea. Not so . Todays tune-up hardly was worth the wait or the price based on the results. While a 5 watt HT 10 miles away could work the repeater, now 25 watts from a roof top antenna is now just about full quieting. Fifteen watts does not make the repeater through the same roof top ground plane. Does logic dictate that we go back to seat of the pants tuning and cast fate to the wind? - Mike No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.5.6/1579 - Release Date: 7/29/2008 6:43 AM
