[EMAIL PROTECTED] wrote: > I think it's an HP of some sort but someone is using it > right now and we have to get it back. The person who owns > it actually has 2 of them but one needs some work and he > is probably going to sell it rather than fix it.
If it's an HP 8920 series, that's virtually top of the line for analog repeater work, and it would be very wise of you to both get it back (!) so it doesn't wander off, and also to learn how to use it. They're worth a bunch of $. There's virtually nothing you can't fix and/or measure/see with one of those... especially if they have the Spectrum Analyzer/Tracking Generator option installed, which you said it doesn't have. But even without it, if it's an 8920 series, that's an excellent piece of test gear. If it is one of the later model HP's, you shouldn't waste any time in learning its features and how to use it! Be cautious, some models (ones with the option for high accuracy) have power input limitations, and you can damage them if you put too much power into them. They're usually labeled clearly with the power limitation near the input N-connector. Get it in-hand, get the model number off of it, and ask here on the list for assistance... a number of folks here can help with how to set up basic tests on your repeater with that test gear, if it's what I think it is. I'm not going to guess, though. Guessing leads to assumptions and that leads to ... well we all know what the word assume stands for -- but it also leads to poor repeater performance. (GRIN) The number one advice I got from veteran repeater-builders when I started working on these things... don't guess. Be scientific. Measure everything, measure again, then compare the measurements against the manufacturer's specifications for the radio. If they don't match, come up with a theory and then make incremental changes to alleviate the problem(s) one at a time, re-measuring along the way. A scientific versus an "amateur" approach, if you will. It'll pay big dividends in your repeater's performance, and also in maintenance time spent hunting problems down. It's a lot easier to KNOW what's not performing to spec versus guessing or "hunches". The basics are: - Everything on-frequency (receiver and transmitter/exciter), and deviation levels set accurately? (Your service monitor can help here, as long as it's accurate... good to make sure when starting with an unknown service monitor, and to always check its receiver against a known source before starting on-site checks.) - Whether or not the system exhibits any desense (easiest test of all... already documented in previous posting) - Receiver sensitivity without antenna system connected. (Known power level signal generator/RF signal source needed here and preferrably a way to measure the 12dB SINAD point.) - *Usable* receiver sensitivity with antenna system connected (Iso-T or directional coupler additionally needed, and a way to measure the 12 dB SINAD point of the receiver.) ^^^ All of the above affected by whether or not you have a pre-amp installed, the quality of your interconnect cables, and transmitter power versus isolation offered by your duplexer. Other things which can factor in: - Transmitter "cleanliness" -- is it clean or is it throwing crud up and down the band. (A great way to become an unwelcome neighbor to all, very quickly.) - Antenna performance (does it duplex well?) - Feedline quality (forward loss, return loss -- how much RF can get through that cable?) - Site noise or other high-power transmitters (even transmitters off-frequency outside the ham bands can overload the front end of low-quality receivers if they're really powerful on a nearby antenna!) Etc etc etc... it's really good to measure everything before starting and then, as I mentioned, make incremental changes and see what helps and knowing exactly how much. Your repeater users will love it if you can squeak the maximum performance out of your systems. Although, there's always going to be "that guy" who wants to hit the repeater using 150 mW from his basement 20 or more miles away... some people just don't realize when they're asking you to push the laws of physics and the typical performance of radio gear right to the limits! (GRIN) Nate WY0X
