[BC] Directional FM Antennas

[Mark Humphrey]

I have an Gates FM antenna brochure from the late '60s with a photo of
the original pole-mounted directional antenna supplied to WMSH 106.7,
Hershey, PA (now WMHX).

It's somewhat unusual in that it used a PAIR of "Cycloid" loaded ring
radiators at each of four levels to form the horizontally-polarized
pattern.  One set of these bays was fed from a common rigid line on
the back side of the pole, but the other set of rings (identical in
appearance but lacking a feedline) was spaced about a
quarter-wavelength out on the front of the supporting pole and
apparently acted as parasitic directors.   Interleaved between these
horizontal directors were four vertical dipoles (Gates/ERI Type 300G)
which used the pole as a reflector in a more conventional manner.

This station eventually negotiated an agreement with its neighbors on
106.5 in Bloomsburg, PA and Baltimore allowing all three to operate
non directional with full Class B facilities, so the antenna is long
gone.

Mark

On Thu, Feb 18, 2010 at 8:58 PM, Tom Dimeo <am at pa321.net> wrote:
> 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?