[BC] More tower sites from above...

[Rob Atkinson]

Okay thanks; I did not know about this. (been out sick.)

Rob Atkinson

From: PeterH5322 at aol.com
Reply-To: Broadcast Radio Mailing List <broadcast at radiolists.net>
To: broadcast at radiolists.net
Subject: Re:  Re: [BC] More tower sites from above...
Date: Fri, 13 May 2005 20:14:35 EDT


 >the KDKA tower looks a bit taller than I would expect for its frequency.

It is a sectional radiator, with a 115 degree bottom section (with 10
degrees of top-loading of the bottom section), and is 264 degrees tall
(with 16 degrees of top-loading of the top section).

The height is about 1.5 times that height which is required for a minimum
conforming Class A radiator, so it does indeed look a bit taller than one
would othewise expect.

Not withstanding that incredible height, 280 degrees, total, the
performance is comparatively poor, at only 431 mV/m/kW at 1 km.

WHO's 300 degree sectional, which is about 50 years older than KDKA's,
does 471 mV/m/kW at 1 km.

WHO's sectional is 180 degrees over 120 degrees.

KDKA's sectional is roughly 155 degrees over roughly 125 degrees.

Seems, if one is going to allocate total height to the two sections,
preference should be for the top section being close to a half-wave, even
at the expense of a shorter bottom section.

180 degrees over 180 degrees is a Franklin, and that can do 510 mV/m/kW
at 1 km, which is nearly 100,000 watts out for 50,000 watts in, using the
Class A minimum as the reference, and is nearly 165,000 watts out for
50,000 watts in, using the Class B minimum as the reference.

WOAI's old radiator was 120 degrees over 120 degrees, and it performed
pretty well. Apparently not well enough, however, for a sectional to be
installed as its replacement, when WOAI's Tx site was moved a number of
years back.

WOAI's current radiator is 194 degrees, about average for a ND-U Class A,
and it also performs about average for such a radiator, at 400 mV/m/kW at
1 km.

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