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Old August 29th 04, 11:16 PM
Peter H.
 
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At medium wave (AM Broadcast) many Class A stations (formerly "clear channel")
use antennas of about 190 or 200 degrees tall.


A Clear Channel is a Clear Channel is a Clear Channel. Any of 540, 640, 650,
660, etcetera.

The average height over all ND-U Class As is 195 degrees.

The real goal here is to get 400 mVm/kW at 1 km, or better, without also having
high-angle radiation which could cancel the groundwave in the fringe area ...
that area where the primary service area ends and the secondary service area
begins.

Taller than about 200 degrees requires sectionalization to do this.

225 degrees is a real killer for a Class A, but is perfectly fine for a Class B
or C, which doesn't have a large primary service area, anyway.

The best performing Standard Broadcast radiator is 360 degrees tall, and
consists of a 180 degree bottom section, and a 180 degree top section.



The FCC requires a minimum antenna effectiveness for that class which is higher
than for the other classes of stations.


362.10 mV/m/kW at 1 km for Class A.

281.63 mV/m/kW at 1 km for Class B and D.

241.40 mV/m/kW at 1 km for Class C.

Of all lower 48 Class As, two don't have conforming radiators, and both of
these are in San Francisco.

Of all Alaska Class As, only one has a conforming radiator.



The base impedance of these sticks near a half-wave tall is going to be pretty
high - and all but one US Class A
station run 50 kW.


The only such Class A in the lower 48 is 1560 in Bakersfield, CA.

There are numerous such Class As in Alaska.