Any comments on the difference between expected antenna patterns and coverage on a DB222 vs. Celwave/RFS PD220?
I'm using a PD220 and find the local coverage to be somewhat spotty, but coverage 20 miles away to be excellent. Is this typical of the PD220? Would a DB222 fill local areas any better? --- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> wrote: > > Dipole phasing is not easy even for the Decibel 420 type antennas. > It is common for very sharp nearfield nulls and cancel areas > expecially near and underneath a mountain top mounted antenna. > I label the effect something similar to what I call unwanted > nearfield/local re-entrant energy. > > Less of a similar antenna in the case of the DB-408 would have > less gain but less close-in and below problematic areas. It > would also have a different vertical radiation angle. > > Using at least one of all the Decibel DB-408 and DB-420 type > antennas from a mountain top repeater site... I can tell you > first hand there is quite a bit of difference in portable and > distant in-building coverage using the higher gain Decibel DB-420 > antenna. There is also something to be said for what I call the > antenna capture area, which is the shear amount of dipole surface > area (metal) spaced up and down many wave-lengths on the tower. > > In most cases there should never be "too much antenna" but there > can be the wrong antenna for an application and location. > > One sidebar I noticed in your post... you weren't using a Decibel > DB-420 Brand Antenna. The Signals Brand Antenna first used in your > system is a different animal indeed. > > cheers, > s. > > > > > "Chuck Kelsey" <kelsey@> wrote: > > > > 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 > > kb7m@ > > 801-224-9460 > > >
