At 10/10/2009 07:13, you wrote: >Milt, > >You gave an excellent description of the problem, and I agree that a lower >gain antenna is called for. However, there is a "dirty little secret" >regarding fiberglass vertical antennas with electrical downtilt: Their >vertical patterns are quite "spoky," meaning that there are many peaks and >nulls. For example, one of the local radio clubs has a Celwave Super >Stationmaster antenna with electrical downtilt on a nearby mountaintop >repeater. The downtilt was chosen in good faith to provide close-in >coverage of users living near the base of the mountain. Over time, we found >that there were many areas where you had line-of-sight to the repeater but >could not get into it from a handheld. But, you could move closer or >further away and then get in, full-quieting. This phenomenon was repeated >at intervals. > >Bottom line: Electrical downtilt is not as simple as it sounds, and it >should be employed only after careful study of the antenna radiation >patterns and the desired coverage areas. > >73, Eric Lemmon WB6FLY
A long time ago I remember seeing ads in a trade mag. for antennas with "Null Fill" made by Bogner. The idea was to "wash out" the nulls below the horizon so users close to the system but behind some local minor obstruction wouldn't lose coverage. Not sure what happened to the company. I do see some other manufacturers use that term, but only for antennas above 700 MHz. Bob NO6B
