[BC] Directional FM Antennas

[Mike McCarthy]

FM DA's a an entirely different approach.  The antennas are field verified
on a calibrated antenna range using any one of a number of approaches to
directionalize, including the use of parasitic elements in both
polarizations.

They are not monitored like AM's because the parasitic elements are
passive and the radiating elements are typically in some sort of absolute
phase relationship. AM DA's monitor only the active driven towers...though
I know of some who have co-located towers on site and they monitor the
detune co-located tower's current as well.

MM

> Are directional FM transmitting antennas phased in a similar
> way as AM directional systems?  If so, is phase monitoring,
> loop current monitoring, common point monitoring etc. required?
>
> If the directivity is accomplished using parasitic elements
> as many amateur antennas do, are the directional
> characteristics monitored in some way?
>
> Tom (just an amateur) does it show?