[EMAIL PROTECTED] wrote: > I had them tuned because I had just bought them and didn't > really trust that they were right. They were very far out > so it's good that I got them tuned. I was having the same > problem as now though very poor receive. Right now I have > a radio on there for receive that was getting about 30 > miles of coverage as an Echolink link node with home made > antenna and now hooked up to the repeater using a big Tram > Dualband antenna through the duplexer I am lucky if I am > getting 3 miles. > > So I don't think the repeater's built in receiver is the > problem which leads me to either desense or a bad antenna > cable. Transmit is getting out very well and the swr is > almost 1 to 1 so I think the cable is OK. I am running > LMR 400 up the tower 95% of the way. I just have a short > coax jumper that goes into the antenna. > > I am going to try to split them and see what I get. > > Thanks, > Vern > KI4ONW
Before you do that. Have someone transmit a weak signal (or use an iso-T and transmit it in yourself, as someone else mentioned) into the repeater while you're at the site, listening to the receiver while the transmitter is on. Turn the transmitter off. If their signal gets better, you're fighting desense. It's that simple to find out. To find out exactly how bad it is, feeding a weak signal into the receiver with an iso-T and measuring the audio coming from the repeater receiver with a SINAD meter is the "next level" of knowing what's going on. (I've seen people do this by ear with practice and get close, but you need to see it on a meter first or have someone demonstrate to even try it. Hey... sometimes when you're starting out you don't have the gear, we understand...) Feed a weak signal (usually 12 dB SINAD for these tests, as a standard starting point) and then turn the transmitter on. The weak signal will disappear or be noisier if you have a desense problem, as mentione above. Increase the signal generator to the point where the weak signal is the same as before (usually 12 dB SINAD is used when you have a meter). The difference between where the signal generator was level-wise when you started, and where you end up, is how MUCH desense you're fighting, and how much more isolation you need in the overall system to make it work. Plus if gather numbers like this, folks here can tell you "ballpark" numbers to expect from your particular radio and setup. Also be forewarned, some antennas simply don't "duplex" well... it's difficult to explain, but you'll find antennas that throw all sorts of crap around when used in duplex operation, that are fine for simplex. I know nothing about the Tram antennas, but "dual-band" antennas for repeater operation, sets off warning bells for me. Use the best cables for interconnect you can possibly buy! Having nice double-shielded stuff built onto the duplexer by the manufacturer, only to run lossy/leaky crud from the repeater to the duplexer, is just asking for trouble. If you used your LMR 400 for that, good... it'll work in most cases, just fine. Many people do have problems with LMR 400 in duplexed service, other's don't. There's a long thread about it around here somewhere in the archives... If you can afford/get hardline - always do it. 1/2" will work fine at VHF unless you have an enormous run, and you might want 7/8" for UHF, depending on the length of your run. Keep an ear to the ground and scrounge hardline any which way you can. Hardline connectors too. They're not cheap. You can test your "inside" setup by replacing the antenna with a GOOD dummy load rated for the power you're pushing, and that is a solid 50 ohm load. (Don't use a cheap one for this. Find something big and stable. I found a 500W Bird load at a hamfest once for $12, best purchase that year.) See if the system desenses itself when not hooked to the outside antenna. If it does, you have something wrong right there in the repeater itself. Stop and figure that out. I could go on and on, but will stop and give the admonishment my elmers gave me... "MEASURE IT"... don't guess. Beg, borrow or steal test gear and get someone to show you how to use it. You can "stumble" into correct setups without it, but you can KNOW how well your repeater performs if you measure. - Receiver sensitivity -- put a very weak calibrated signal directly into the receiver and measure the 12 dB SINAD point. - Useable receiver sensitivity -- do the same test, but with an iso-T or directional coupler of known loss (measure that too!) and see how much more signal you need to have the same receiver performance through the duplexer, and final cabling. [If you have a pre-amp this becomes more important to see if the gain has driven the receiver into the noise floor at the site, and/or if you're overdriving the receiver with too much RF.] Those are good starting points, both with the transmitter on and off. Nate WY0X Nate WY0X
