Could be a "bad-out-of-the-box" antenna. I've heard of this happening with fiberglass antennas. It could be broken near the bottom and still show good VSWR but give you no gain.
Chuck WB2EDV ----- Original Message ----- From: "Cort Buffington" <[EMAIL PROTECTED]> To: <Repeater-Builder@yahoogroups.com> Sent: Thursday, October 16, 2008 9:16 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 >
