At 12:41 PM 11/05/07, you wrote: >Let me start by saying that I have been around ham repeaters for a long >time but I have not set one up this way. I have been given the >opportunity to use a 220 foot tower near the high school radio club's >location. We are being allowed to mount one antenna at the top and use >of the building at the base. We have two repeaters one on 145.35 and >one on 444.625 that will need to use one antenna. I need advice on the >antenna choice and diplexor for the setup. I know this may not be the >best solution but it is what we are allowed. We have 300' of new >andrews 1/2" hardline and new connectors and hardware donated by a >former student of mine. Any advice would be appreciated. > >Charles Lowery, NM4V
Depending on wind loading you might want to go with one antenna or two on one mast...... One option is to ignore the top, and side mount a 2m and 440 dipole array (let the tower take Thors wrath)... I don't know what the budget is, but I had this mental image after reading your posting... "Hello, Andrew sales?" (Andrew bought DB a while back) "I'd like to have you make me a combination DB408 and a DB224 on a single mast with, with two feedlines. I have a political situation where I can only mount one antenna, and if you could sell me that combination as a single part number that would satisfy everyone". They have a 41 foot long mast that they use on the DB228 product ... it arrives in sections that are field assembled. If that does not fly, and you are limited to a stock product, look at the DB-314 - it is 8 UHF dipoles (a DB-408, 6.6db gain) and 4 high band dipoles (half of a DB-304, 3.2db) on the same mast with separate feedlines. Or make up your own by buying a DB408 (about 10 feet long) and a DB224 (about 23 1/2 feet), both with the mast deleted, then mount both on your own mast (about 35 feet long) . You show up with this extra long, but singular "antenna" and mount it.... However you do it, you will want to run two feedlines, and make sure they are both Heliax (i.e. 100% shield). I still remember the nightmare where someone had tiewrapped two coax cables together then tiewrapped the bundle to the tower leg... 97% braid equals 3% holes facing each other for over 100 feet. Made a nice distributed coupling line and a totally overlooked source of desense. If you are limited to one feedline use a pair of commercial-grade TX-RX Corp. diplexers, one on the top (in a weatherproof NEMA box) and one in the building. Mike WA6ILQ
