Terry, In lieu of the ideal bench equipment, yes, the IC-2710 is better than a handheld, since its impedances are supposed to be close to 50 ohms at the connector. You are to be commended for your creativity in making do with what you have. Since your duplexer has been moved from its original settings, you can only improve matters.
Let's review your process: You generate your 449.625 MHz receive signal with the service monitor, and inject it into the duplexer's antenna connector, with your monitoring radio set to 449.625 MHz and connected to the RX (high pass) connector of the duplexer, and a 50-ohm dummy load on the TX (low pass) connector of the duplexer. The SINAD input of your service monitor is connected to the monitoring radio's speaker, and you adjust the center rods of the high-pass cans to get 12 dB SINAD with the lowest level signal at the RX connector. Next, without changing any of the connections, you set the service monitor to generate 444.625 MHz and program the monitoring radio to receive 444.625 MHz. With your service monitor generating the highest-level signal possible (at least 0 dBm, but higher is better), you adjust the notch capacitors on both high-pass cans to minimize the received signal. You might get better results by monitoring the RSSI voltage at the radio. Do not move the threaded tuning rods at all. Next, reverse the positions of the monitoring radio and the dummy load. The service monitor is still generating 444.625 MHz at a high level, so bring the output level down to about -100 dBm or so. While monitoring the SINAD meter adjust the center rods of the low-pass cans to achieve 12 dB SINAD with the lowest possible output of the service monitor. Finally, set both the service monitor and the monitoring radio to 449.625 MHz. Crank up the output level of the service monitor to maximum, and adjust the notch capacitors on both low-pass cans for a minimum receive signal. Again, you might need to meter the RSSI voltage as you tune the notch capacitors. Repeat all four steps above until there is no improvement, since there is always some interaction between the low-pass and high-pass sides, especially if significant changes are made to either side. The primary disadvantage of this simple procedure is that the output level of the service monitor may not be high enough to achieve a sufficient signal at the notch frequency to get the tuning exact. It is true that duplexer tuning can be affected by rough handling, especially if one of the cavities gets dented. However, a high-quality duplexer is seldom affected by temperature, because the center tuning rod is normally made of Invar- an alloy that minimizes sensitivity to temperature. Keep in mind that the shack temperature is not the only factor to consider; a typical six-cavity duplexer on a 250-watt repeater will be heated by the transmitted carrier due to insertion loss of 2.2 dB, amounting to about 100 watts lost inside the cavities. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of terry dalpoas Sent: Sunday, September 20, 2009 9:41 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] UHF Duplexers Eric, I did find my old Icom IC-2710 dual band mobile last night. Would that be okay to use instead of the HT? The only reason I thought the duplexer needed to be tuned was after we got it loaded in the truck, some stuff shifted (rough mountain road), I thought that they may have gotten bumped. I am not sure how durable duplexers are, but I have heard sometimes the slightest shock can mistune them, and I discovered the tuning rods were not locked in place. I do hate to sound like a dummy on these things and sorry to keep bugging you on it. Last repeater and duplexer I messed with was in 2002 (at the age of 22 before I was married and had a kid, and was my first repeater), and am relearning this stuff. The one I am working on now is my first 70cm. I was told these things are addictive, and I like the challenge (not the headaches, though). Terry, KM5UQ ________________________________ From: Eric Lemmon <wb6...@verizon.net> To: Repeater-Builder@yahoogroups.com Sent: Sunday, September 20, 2009 11:25:03 AM Subject: RE: [Repeater-Builder] UHF Duplexers Terry, I understand and appreciate the fact that you are forced to employ a makeshift procedure for duplexer alignment, since you do not have the proper equipment (spectrum analyzer with a tracking generator, or the best choice- vector network analyzer, aka VNA). While it is very true that one can get fairly close with a handheld radio as a detector, close is not always close enough. The most obvious problem when using a handheld radio is that the antenna connection on a handheld is very seldom optimized at 50 ohms. Even if the rubber duck antenna has a BNC connector on it, one cannot assume that the radio's source and load impedances are even close to 50 ohms. Since a rubber duck antenna is usually nothing close to 50 ohms, the radio-side impedance is more likely whatever will be close to matching the antenna. I found this out the hard way, when both of my Icom IC-2AT handhelds (remember them?) suffered blown final transistors when I used them on a roof-mounted quarter-wave whip on my car. My mobile antenna was carefully tuned to be close to 50 ohms, but the handheld radios were not a good match, and the finals blew. Most commercial portables- the Motorola HT1250 is a good example- must use a special BNC adapter to convert the normal antenna matching circuit to 50 ohms for use in bench testing or to connect an external antenna. So, I suspect that your tuning method is resulting in a mis-tuned duplexer that does not properly match your repeater. If you possibly can find a shop that has a VNA, pay to have it tuned precisely to your repeater pair, and do not touch any of the adjustments afterwards. The next best choice is a shop that has a good spectrum analyzer with tracking generator, and used with a return-loss bridge. The benefit of a VNA or an RLB is that the tuning of the bandpass function for the best return loss is far more sensitive and precise than tuning for minimum insertion loss. The return (reflection) loss is seen as an extremely sharp spike or notch, while the transmission loss is just a broad curve. Too, a VNA has precise 50 ohm matches on all ports. Once you've used a VNA to tune for return loss, you'll wonder how you ever managed without it. No matter what laboratory instrument was used to tune your duplexer, try to avoid the temptation to "tweak" it once it is installed. In every instance of which I am personally aware, the careful shop tuning of a duplexer was negated when a "diddle-stick artist" could not resist the temptation to "improve" the tuning at the site. But, I digress... If you have checked all of the connectors, jumpers, and feedline for problems and found none, I still believe that your duplexer is not tuned correctly. Since you state that the duplexer in question was used on the repeater for more than a decade with no problems, and presumably on the same frequency pair, why are you re-tuning it? You probably have heard the old saying: "If it ain't broke..." 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@ yahoogroups. com <mailto:Repeater-Builder%40yahoogroups.com> [mailto:Repeater-Builder@ yahoogroups. com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of terry dalpoas Sent: Saturday, September 19, 2009 5:58 PM To: Repeater-Builder@ yahoogroups. com <mailto:Repeater-Builder%40yahoogroups.com> Subject: Re: [Repeater-Builder] UHF Duplexers Eric, The repeater is 70cm amateur (444.625 TX/449.625 RX). These duplexers have been used on this same repeater for I'd say 10-13 years. I was given the repeater by the previous owner because the site was lost and he did not have time to repair the problems that did show up (the PA went out). I had a mobile PA that I turned down and used it and ran the repeater from my house for a few months (ran fine), then disconnected it. It sat in my shop from Oct 2008 until around 1 month ago. It was not as before. I wound up basically rebuilding the receiver, and I rebuilt the original PA. However, this year in Oklahoma, we did get a lot of rain and it did get pretty warm in my shop (along with high humidity. I wonder if the heat and humidity might have done something to the duplexers. I do have another set of these that were on the link transceiver (the link was set up to run full duplex as well), I may retune them to see what I have. Equipment and tuning method. Here is what I was taught how to do it. I use an IFR 1200S service monitor, and the only spare radio I have at the moment is an Icom T7H HT. I start with RX (449.625) first. I connect the IFR to the antenna port, a receiver on the RX port (high pass), and a dummy load one the TX (low pass). I adjust RX pass freq for best SINAD. I then change the receiver and IFR to the TX freq and adjust for the best rejection, or worst SINAD. I do the TX (444.625) side the same way, best SINAD TX pass, worst SINAD RX reject. I tuned a set of duplexers this way before on a 2m repeater using 6 cavity Sinclair BpBr with no problems, this is the first I have messed with a set of Wacom's. Terry KM5UQ ____________ _________ _________ __ From: Eric Lemmon <wb6...@verizon. net <mailto:wb6fly%40verizon.net> > To: Repeater-Builder@ yahoogroups. com <mailto:Repeater-Builder%40yahoogroups.com> Sent: Saturday, September 19, 2009 6:30:57 PM Subject: RE: [Repeater-Builder] UHF Duplexers Terry, Is your repeater in the 70cm Amateur band? If so, and your WP-678 duplexer was not originally tuned for that band, that may be where the problem lies. I have a Remec-Wacom WP-678 duplexer that I bought from the factory for GMRS service, and its insertion loss at the transmit frequency is 1.14 dB, equivalent to 38.5 watts out for 50 watts in. Your duplexer's measured insertion loss exceeds 4 dB. Most Wacom UHF commercial-band duplexers will tune down into the Amateur band, but not all of them. It appears that your duplexer is tuned improperly, or it may be impossible to tune it to your pair. What method and equipment are you using to tune the duplexer? 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@ yahoogroups. com <mailto:Repeater- Builder%40yahoog roups.com> [mailto:Repeater- Builder@ yahoogroups. com <mailto:Repeater- Builder%40yahoog roups.com> ] On Behalf Of terry dalpoas Sent: Saturday, September 19, 2009 2:11 PM To: Repeater-Builder@ yahoogroups. com <mailto:Repeater- Builder%40yahoog roups.com> Subject: [Repeater-Builder] UHF Duplexers Just about finished with the Mastr II UHF repeater. I've run into a problem with the duplexers. They are a set of WACOM BpBr Model WP678. I am putting 48W into them, but only 18.5W out. I believe this should be better. RX will open squelch at around .2-.3 uV through the cans (this I know is OK). Could there be a problem with the TX side of the cans? Terry KM5UQ __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
