[BC] Directional FM Antennas

[RichardBJohnson at comcast.net]

At Jampro, the antenna to be characterized was mounted on a tower section of the exact kind that the customer would use. The tower section was then mounted horizontally like a pig on a spit. The tower feed was connected to a receiver and the tower was illuminated by a remote-controlled signal generator in the far field. The spit was turned and the horizontal pattern plotted. The whole assembly was then rotated about the horizontal axis (to be able to plot the vertical pattern) and the measurements were repeated. The horizontal plot was automated, but for the vertical one needed to manually move the antenna support assembly and redo the horizontal plot. The result was a number of horizontal plots, each showing the vertical radiation pattern.

When I was in Sacramento, they always used the customer's antenna, never a model.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Dave Hultsman" <DHults1043 at aol.com>

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