Cort, One problem that I don't think has been mentioned, is the possibility that the center conductor of the feedline to the top antenna has somehow disconnected from the center pin at the top end. This doesn't happen very often with foam dielectric Heliax, but it does happen often with air dielectric feedline. When the sun beats on the black exterior of the feedline, it expands longitudinally, but more on the outside than on the inside. After many cycles, the center conductor pulls out of the back of the center pin. On captive-pin Heliax connectors, it looks like the center pin is fine when viewed from the top, but there may be no connection to the cable's center conductor. One quick way to check this is to measure the DC resistance between the center conductor and shield at the bottom end of the feedline, where it connects to the duplexer. When a DC-grounded is properly connected at the top, you should measure close to zero ohms plus the loop resistance of the feedline.
Incidentally, this quick and simple measurement is a good one to make on any new installation, right after it is certain that everything is working properly. The measured resistance value should be posted somewhere in the shack so that it can be verified from time to time, or when there is a suspected problem with the antenna or feedline. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Cort Buffington Sent: Thursday, October 16, 2008 7:38 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] UHF Repeater Antenna Discussion Don, two completely different antenna and feedline systems. I swap them where each separate antenna/feedline system connects to the duplexer. The Telewave meter is new because I didn't trust my ham-type meters... (I've needed a real meter for years anyway) The Telewave shows a little less forward power and a little lower VSWR than the cheap comets. I did a quick check of the telewave by transmitting various signal levels into my IFR 1200S (currently in calibration from Aeroflex) I then transmitted the same signals into the telewave with a nice big DB load I've trusted for years on it. The Telewave was within a few % of the IFR. I know that's not a perfect method, but new meter, agrees with IFR in my limited testing format. I'm probably pretty confident of it. Problems before and after vertical alignment. If the feedline/connector is damaged it was damaged when we put this system up -- from tower on the ground. I mean, we did it ALL three weeks ago. Saturday morning there was a pile of parts, by sundown it was all assembled and installed. No rain at all between erection and the first round of testing. After significant rains, no change. Thanks Don! Cort On Oct 16, 2008, at 9:24 PM, Don Kupferschmidt wrote: Cort, I need to understand if I have all the information correct from your post. One 440 machine. One duplexer. Two antennas connected to two feedlines which can either be terminated to the duplexer as you so desire? Only one feedline to one antenna, not coupled or combined in any way? One hardline / antenna works good (DB420) and one hardline / antenna (Telewave ANT450F10) works bad? The first step is to verify the Telewave wattmeter. I'd get a hold of a Bird 43 or equivalent and verify your readings. That's the easiest thing to do. If your forward / reverse numbers are accurate then I'd suspect the Telewave system or it's hardline, unless proven otherwise. You need to rule out either the antenna or the hardline by substitution, and one at a time. Possible issues could be bad connectors either at the antenna base or duplexer termination. How long ago was the antenna system put up? Was there some heavy rain in the area that water could have been introduced into the connector / hardline if they weren't properly water-proofed? Unless someone contradicts me here, I'm having a hard time believing that the vertical alignment of the Telewave is critical. In re-reading your post over a couple of times I'm wondering when you checked the alignment and then implemented a little down-tilt you may have done something wrong to cause the hardline / antenna system to react that way. Keep us posted and good luck with finding out the problem. Don, KD9PT ----- Original Message ----- From: "Cort Buffington" <[EMAIL PROTECTED] <mailto:cort%40lawrence-ks.org> > To: <Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > Sent: Thursday, October 16, 2008 8:16 PM Subject: [Repeater-Builder] UHF Repeater Antenna Discussion > Folks, > > My repeater partner and I have recently placed our new 440 machine. We > have realized some odd issues. We bought a new Telewave ANT450F10 to > put on top of the 100' tower, fed with a new piece of Andrew 5/8" > heliax. We also side-mounted an old DB420 with the top a few feet down > from the top of the tower with about 85' of old 7/8" Andrew heliax. > So, we put smokin' new gear on top, and smokin old below it. The DB420 > is spaced correctly from the tower and is set up with each half 90 > degrees rotated. > > The tower is on relatively high pasture land (for NE Kansas anyway) > with a nice clear view all around. I'll not say we're on a hill, but > on relatively high ground. We are attempting to cover two towns > approximately 25 miles apart. We are 1/3 of the way from town 1 to > town 2 and about 3 miles N of the highway that pretty much is a > straight shot connecting them. > > The Telewave setup on top performs poorly. The DB420 on the side is > working great. By this difference, I mean signals that are getting in > full quieting on the DB420 are very noisy on the Telewave. Transmit > differences mirror receive. S9 reception on the DB420, switch to the > Telewave and it's S1-S3. We experience this phenomenon in all > directions. > > Wattmeter (yes, it is a "real one" -- Telewave 44) says that things > look good as far as loading both antennas -- DB420 is 1.43:1, F10 is > 1.39:1. We are about to climb and take readings at the top to make > sure there is no feed problem with the Telewave 'F10, and I admit that > has not been done yet. We did have a discussion with Telewave, who > advised that vertical alignment of the F10 (as they refer to it) is > critical. We have checked alignment and even implemented a little down- > tilt in the most important direction (just a few degrees). We see not > real appreciable difference. > > For you repeater elmers out there: If we don't find a problem with the > feedline on the Telewave antenna, does this make any sense? Telewave > also HIGHLY recommended that the F10 isn't a good fit for this > installation due to its extremely narrow vertical beamwidth, and > recommended that a 4-bay dipole of theirs would be MUCH better because > of the ability to tune the pattern to our desired coverage area and > the increased vertical beamwidth. I always thought I wanted NARROW > vertical beamwidth to keep the RF on the horizon. I would have thought > that 100' up on relatively high ground (this is Kansas, after all) > wouldn't have a real problem shooting over the top 10 - 30 miles away. > > In any event I seek advice and wisdom, and yes, we are planning to > check the coax for loss at the earliest convenience. I would like to > take advantage of the top slot on the tower for improved performance > rather than stay on the lower spot, and will try another antenna if > necessary. I'm just having a hard time imagining that the F10 has > appreciably narrower vertical beam as a 9.something dBd antenna than > the F10 as a 10dBd antenna, etc. etc. And it also seems counter > intuitive that a taller vertical beamwidth and less gain on the > horizon in this application would be better. I trust the experience > and knowledge of Telewave, but I also trust the wisdom from this list, > which has saved me many times. > > Your thoughts gentlemen? > > -- > Cort Buffington > H: +1-785-838-3034 > M: +1-785-865-7206 > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > -- Cort Buffington H: +1-785-838-3034 M: +1-785-865-7206
