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" <purvis...@...> 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 > > > > > > __ > > > > > >
