[BC] EARLY KDKA ANTENNA

[PeterH5322]

>An interesting exercise would be to overlay the vertical field strength
>graphical profile of a 190-degree radiator on top of a true Franklin, along
>with a few of the quasi-Franklins you mention.  

At my suggestion, Richard Fry did NEC modeling of:

1) 195 degree non-sectional (the average over ALL U.S. ND-U Class A 
non-sectionals),

2) 120 over 120 (WOAI),

3) 180 over 180 (WHO), and

4) 180 over 180 (true Franklin, and the only radiator which the FCC 
actually calls a Franklin).

Also 225 degrees.

A high-angle vertical lobe will be present in any non-sectional radiator 
which is taller than 180.

The high-angle vertical lobe was just about to be formed in the 195 
non-sectional case, and the exceptional performance of this radiator ... 
standard equipment at CBS O&Os and several others ... is undoubtedly why 
it is so popular with Class As (about 405 mV/m/kW at 1 km).

By 225 degrees, this high-angle vertical lobe is so strong the radiator 
is useless for Class As (as was proved in the initial installations of 
WSM and WCAU).

Yet, 225 degrees is almost perfect for a Class C, which doesn't have much 
of a primary service area, anyway (about 440 mV/m/kW at 1 km) [ * ] .

In theory, sectionalizing a taller-than-180 radiator can eliminate this 
vertical lobe, but NEC modeling showed that this wasn't the case.

High-angle vertical lobes were present in 120 over 120, 180 over 120 and 
180 over 180.

On certain frequencies, and with particular first-hop skip distances, the 
high-angle vertical lobe is tolerable, however.

180 over 120 was successful on 1040 at WHO. 120 over 120 was successful 
on 1200 at WOAI.

180 over 180 is considered a success on 1500 at KSTP (day only) and at 
KFBK (two identical radiators in a DA-2 configuration).

If WTOP really wanted to improve its DC and suburbs signal, a set of 180 
over 180s in a DA-2 configuration could do the job, as 50 kW into such a 
radiator gives the equivalent of 99.2 kW into a minimum conforming Class 
A radiator (510 mV/m/kW at 1 km vs. 362 mV/m/kW at 1 km).


[ * ] 440 compared to the minimum for Class C, 241, gives the equivalent 
of 3,200 watts out, for 1,000 watts in.


Peter