On May 30, 2007, at 3:55 PM, skipp025 wrote: > The hardware description is part of or most of the reported > problem description: > > Wide-band close coupled relatively high/moderate gain antenna(s).
Yup. Recipe for trouble. We tried to tell 'em... but... well, anyway... no harm done. >> away, mixed with god-only-knows-what-else-up-there at that >> almost 6000' HAAT site, from blowing away the front-end of >> their brandy-spankin-new Kenwood every time we keyed up. > > You keyed up how far away (frequency spacing) and at what power > level? Circulators or isolators in use? Did anyone measure the > two antennas - system isolation/coupling value(s). I don't want this to turn into them thinking I'm picking on them, but for the sake of the technical discussion... We're at 145.145 MHz for our output. Their input is 146.07. The temporary antenna was set up 15' away (on a building) from the tower where the 8-bay TX antenna of the coupled systems was direct line-of-fire towards it. If I remember correctly, it was a 4-bay DB. Isolator (of course, in the combiner) on ours... don't know about theirs. Doesn't matter much for their receiver. No measurements of the type you mention were made by anyone that I know of. If there were, it was their experiment and they didn't share. Didn't matter to us, really. We just watched with interest and gave 'em a phone call when we noticed their change had caused us to desense them. (Technically they could have figured that out on their own, but someone pointed out to me that not telling them would have been pretty rude, once I noticed it was definitely us involved... I would have wanted a call from them if I couldn't figure it out and was on the receiving end of that problem. Thankfully, we weren't on the receiving end, so we just called and let 'em know.) Previously they had tried to move their TX off the combiner also, and they desensed/bothered the repeater with a 146.34 input. Their TX was back on the combiner, but RX was on the separate test antenna at the time of the above "story". (Basically throughout this, we all knew others had tried this before, and we attempted to share with the new tech that he was going to run into these problems, but he wanted to see it for himself... which was fine with us -- like I mentioned before, they had a way to remotely switch it all back if major problems had ever popped up. Everyone that ever goes up to that particular site who's never worked on stuff at a high-RF-noise site, thinks they can get back that couple of dB we're all losing in the receive multi-coupler. Problem is, they forget to do a usable sensitivity test and then can't figure out why things don't get better... all they do is pull in another 2 dB of noise... and maybe once in a while, they get a tiny bit better signal from a weak user.) >> We even tried to help out their experiment with an additional >> pass can on our transmitter, losing another 1dB at our output >> frequency before the combiner, to get our signal a few more >> dB down at their input -- didn't help. > > What I would probably expect as a result... Yup. Us too. We were just playing "friendly neighbor" and got burnt by it by blowing our own PA. Dumb. Won't be so "neighborly" next time, probably, as to make a change to our system to try to help someone else's mistake. (GRIN) >> No such problems on the properly tuned/configured combiner - >> multicoupler system. > > If the system was properly designed, constructed and applied. Yep. There is that... gotta do it right. The combiner/multicoupler system was carefully aligned/tuned on a vector network analyzer years ago. We try to tell new techs to leave it the hell alone, but we've heard of at least one group wrenching on their port many years ago... We're lucky, being the "low-side" we're on 2 ports to ourselves, and the two higher machines share their combiner section (then those two are combined to make it a 4-port system). So if someone fires up the golden screwdriver, they usually don't bother us. That might be a point for the guy who was originally asking about such systems... tune/configure it correctly and then threaten to break the fingers of any new repeater tech for any group using the thing that decides they just HAVE to screw around with it. Make sure someone is "in charge" of the combiner/multicoupler system, and keep newbies from messing with it. -- Nate Duehr, WY0X
