Cort, Do you really have 5/8" ? Here are the part numbers for the coax
LDF4-50A 1/2 50 ohms - loss at 450MHz ~1.447 LDF5-50A 7/8 50 ohms - loss at 450MHz ~ .808 LDF6-50A 1 1/4 50 ohms LDF7-50A 1 5/8 50 ohms So if you have the real deal feed line loss doesn't look like your problem If you have something else all bets are off send me what number is on the cable. The Telewave antenna (actuality ANY Telewave antenna) is problematic. We tried using several in the paging business most likely for the same reason you did they are cheap. They never performed as well as advertised. If you want a "cheap" antenna the best for the money is and ASP705K by Decibel Products (or whatever they are this week) They work well have a nice round pattern. And will generally out perform a DB-420 because of less pattern distortion. The statement "The DB420 is spaced correctly from the tower" concerns me as there is no "correct" way to side mount an antenna. You must take in to account the desired v. undesired coverage areas and optimize the mount and elements to achieve the desired coverage. On that antenna with an 18" face tower mounted 16" off the point of the tower set in an omni configuration You will see peaks of around 10.5dBd and nulls of around 5dBd. I see nothing here that would indicate that the Telewave system is performing correctly. Remember to take into the feed line loss when calculating SWR. That is if you are putting a 100 watts into the feed line and get 50 watts back That indicates a fault at the top as you have 100 watts and 2.894dB loss (1.447*2 up and down) that would be half power of 50 watts. Do some more looking before you call the antenna bad. Robert / KD4PBC -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Cort Buffington Sent: Thursday, October 16, 2008 9:17 PM To: Repeater-Builder@yahoogroups.com 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
