I've been following this thread on and off. I was wondering if you tried replacing the 100' plus run of RG-214 with another cable. Or if you have pulled the connectors on each end to see if they are properly installed. (I have had connectors installed by the cable supplier that were bad. in one case a direct short between the shield and center conductor because the cable wasn't properly trimmed, and in another case the shield was deformed during the installation and the distance between it and the center conductor was close enought to short when RF was applied but still not show a short when check with a VOM for continuity.) All it takes is for a couple of strands of the shield braid to be in the wrong place when you key up. to cause all your greif. Also, you might want to do the same with all the other cables (inspect and/or substitute 1 at a time).
Barring that I would suggest you change out every adapter/fitting and right angle connector you have in the system, from rptr. to antenna, one at a time to see if the problem lies there as well. The 100' horizotal distance and 10' vertical distance are not where the problem is. You have got a faulty component os sheilding problem. My 2 cents worth. Doug N3DAB --- In [email protected], "tahrens301" <tahr...@...> wrote: > > Thanks to all... > > I guess it could be corrosion at the antenna, but the one that > is on it now is pretty simple, & not much opportunity for > corrosion. I am going to put up the 2nd DB-224 tomorrow & > see what difference it makes... I don't really think it'll > change much, but it will let me play with the matching unit > I built & see if it works! > > Don - I can put the iso-tee in line, & feed the atten port > into the spectrum analyzer. It should show me if the xmtr > is having problems. However, the current antenna is a > perfect match - no reflected power at all, so I think the > xmtr 'should' be happy. > > The 100' may be the real problem, although everything has > very well made cables, quality RG-214, N connectors, etc. > > Thanks, > > Tim W5FN > > > > > > > > --- In [email protected], "purvissid" <purvissid@> wrote: > > > > You mentioned 100 ft hoz separation, I don't think that is enough, but > > don't have a chart handy where I am now. Sid. > > > > > > > > > > --- In [email protected], "tahrens301" <tahrens@> wrote: > > > > > > Hi Jim & All, > > > > > > Thanks for the info & responses. > > > > > > I took down the 224 & found that the N connector on the > > > end wasn't quite up to snuff. I am going to put a > > > ham antenna on it - think it's a ringo2 or some such thing, > > > just to see how an antenna with good swr will work in the > > > desense arena. > > > > > > Then I'll put up a different 224 & see how it goes. > > > > > > I did see the posting about how to lower the frequency > > > of a 224. Not sure I want to go that route, but might > > > in the end! > > > > > > I built a small matching unit that I'll try out... basically > > > a tuner that will go between the duplexer & feedline. > > > > > > One of the guys talked about using a smith chart & putting > > > some stubs at the feed line which would change the matching. > > > > > > gee, lots of things to experiment with. That's the <fun> of > > > it no? :-o > > > > > > Thanks again, & I'll post my progress. > > > > > > Tim W5FN > > > > > > > > > --- In [email protected], Jim Brown <w5zit@> wrote: > > > > > > > > One of the local repeater operators used an antenna at the top of a 100 > > > > ft tower that got bent over during last winter storms. He put up a > > > > temporary antenna at the tower base and is experiencing some really bad > > > > desense with the low antenna. > > > > > > > > He is using a GE Mastr II base station repeater and had reasonable > > > > operation with little desense on the antenna 100 ft above the > > > > equipment. The antenna only 15 ft or so above the equipment now and > > > > has the bad desense problem. It would appear that the antenna is > > > > flooding the equipment with more RF than the shielding can handle. > > > > > > > > BTW, take a look at some of the previous posts on modifying a DB-224 by > > > > adding a 2 inch extension to each end of each dipole to bring it down > > > > into the ham band. The SWR does not go completely to 1:1, but does hit > > > > a minimum in the middle of the 2 meter ham band. No change to the > > > > harness was required to move the antenna frequency. > > > > > > > > 73 - Jim W5ZIT > > > > > > > > --- On Tue, 9/1/09, tahrens301 <tahrens@> wrote: > > > > > > > > From: tahrens301 <tahrens@> > > > > Subject: [Repeater-Builder] Antenna SWR = Desense? > > > > To: [email protected] > > > > Date: Tuesday, September 1, 2009, 2:03 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi folks, > > > > > > > > > > > > > > > > Just a bit of an update... got the 6 cavity Telewave > > > > > > > > duplexer tweaked up - looks like it pretty much hit > > > > > > > > the specs in the data sheet. > > > > > > > > > > > > > > > > With a dummy load at the 'antenna' port, I used an > > > > > > > > "iso-tee" to inject a signal at both the receiver > > > > > > > > input, and between the antenna port & the dummy > > > > > > > > load. With a weak signal, both places showed me that > > > > > > > > there was no desense. Very weak signal would hold in > > > > > > > > the repeater. > > > > > > > > > > > > > > > > However, putting the system on the antenna (a 150-160 mhz > > > > > > > > DB-224 100' horizontally & 10' vertically separated) > > > > > > > > through a metal building fed with 7/8 heliax, there > > > > > > > > seems to be no end to the desense! > > > > > > > > > > > > > > > > The wattmeter shows 30 watts forward & 3 watts reflected > > > > > > > > at the antenna port, if my math serves, it's less than 2:1. > > > > > > > > > > > > > > > > Can the less than 1:1 match be the culprit? > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > Tim W5FN > > > > > > > > __ > > > > > > > > > >
