We had a DB-420 style antenna (actually it was made by Signals, but it was folded-dipole design) on our UHF repeater at work. We were constantly having difficulty with portables being able to hit and hold the repeater and they were no more than 1/2 mile out. The local M/A-Com shop kept saying "too much antenna." We changed it out to a DB-408 and the problem was corrected. We are in rolling hills and the antenna was about 70' above ground level at a water tank. I plotted the antenna pattern against topographic map data and discovered that the portables were in some deep nulls with the higher-gain antenna.
In another instance, a UHF ham repeater on a pretty decent site was using a DB-420 style antenna (I believe it was actually an Antenna Specialists version). It worked great out at the horizon, but closer in mobiles would become noisy and portables were tough. It got changed to a Sinclair 4-element folded dipole, and the improvement was substantial. Slight loss out at the extremes of the coverage area. I'm convinced that bigger isn't always better. You need to use the right antenna for the intended coverage. If all of your users are out at the extremes of where your repeater is located, the highest gain antenna might make more sense. I'd dare say that this usually isn't the case. Chuck WB2EDV ----- Original Message ----- From: Keith, KB7M To: Repeater-Builder@yahoogroups.com Sent: Monday, November 26, 2007 11:31 AM Subject: Re: [Repeater-Builder] Re: Repeater Antenna Choice The area served by many of our radio sites (we are in Central Utah), sit at approximately a 12 degree downtilt from the sites. Most of these sites are at 3000-4000' AGL. In some cases, we have opted for lower gain antennas to cover close in areas better. We designate repeaters as local or wide area coverage to account for this. Wide area repeaters get high gain antennas to aim for the horizon (about 50-100 miles out), and local area repeaters get lower gain antennas for about 5-20 miles out. In some cases we opt for directional antennas such as corner reflectors or dipole arrays with all elements on one side of the mast when we want to cover the populated areas better at the expense of "the back country". -- Keith McQueen [EMAIL PROTECTED] 801-224-9460
