[BC] FCC Approves proposed AM MoM Rules

[W2XJ]

1 KM to 1 mile represents 10 wavelengths or more for most of the broadcast band.  This is the acknowledged distance for where a pattern is formed.  1 KM will cover down to 1000 KHZ. 1 mile is good to around 600 khz.  I agree that below those frequencies a more distant measurement point is requited.

In arrays with deep nulls a further distance risks interference entering into the equation. $

 

Thomas G. Osenkowsky wrote:

Bear in mind that at 1 km or 1 mile the pattern may
not be completely formed. As a matter of fact, when
considering 'proximity effect' it may never be 100%
fully formed.

Also consider two towers where the complete null is
in line with the towers. Theory tells us the field ratio
must be 1:1 to have a complete null. As you move
away from the array the distance from the farthest
tower is greater than the nearest. So, the required
field ratio is no longer exactly 1:1.

FCC Rule sinusoidal assumptions define an array as
a point source. In practice, it is not.

Tom Osenkowsky, CPBE

> The best way to tune an array if you are doing it by FIM is to set ratio
> points. Drive stakes in a perimeter of 1 KM to 1 mile around the array
> every 10 degrees or so. Do an omni proof for those locations and then
> while tuning measure the ratio. Once those look good, run the necessary
> radials.