[BC] Directional FM Antennas

[Dave Hultsman]

In a message dated 2/18/2010 9:13:09 PM Central Standard Time, tosenkowsky at prodigy.net writes:
>> If the directivity is accomplished using parasitic elements
>> as many amateur antennas do, are the directional
>> characteristics monitored in some way?
 
99999999
 
Typically the install an antenna on the tower modeled exactly as the tower the antenna is to be mounted.
 
In the case of ERI they model at your FM frequency at Shively the model at a higher frequency I believe.
 
The Tower is mounted on a turntable with the antenna and some parasatics. They then rotat the turntable & tower with power from a dipole and measure the pattern for 360 degrees in each plane. From the first measurment the make calculations and add or change positions of the parasatics to adjust the signal as required.  Sounds simple but it is alot of work and very time consuming.  You have to move things on the model tower each time and their work is really precise.   In the case of ERI you can look up thru the roof skylight in the building and watch the tower rotate whil watching the pattern being platted on the computer screen on the desk.
 
Dave Hultsman