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Re: The ever-mysterious tower...

At 06:21 PM 7/6/97 +0000, you wrote:
>In a message dated 97-07-06 12:10:20 EDT, you write:
><< WRCA towers is that all three are guy-wire top-loaded.
> However, you'd have to have incredible eyesight to observe this while you
> drove by. >>
>I've noticed that, plus at least 1 appears to be shunt fed; a small pipe runs
>up about a third of the tower spaced a few feet away. Seen from 128
>southbound when the sun reflected well.
Neil Dunn made the same assumption about the "back" tower being shunt fed.
Could be. I don't know, but I don't think so. When I saw that "pipe," I
assumed that it carried the wiring to the tower lighting (no longer used on
that tower) and that enclosing the wiring in metal had something to do with
maintaining the stability of the pattern. The only notation in the FCC AM
database is that the towers are top-loaded. I think that if either tower
were sectionalized, that fact would be noted.

When the station was WCRB, it had three 200' towers on an east-west line. In
those days, WHAZ, Troy NY (then owned by my alma mater, RPI) was a
share-time station that operated at night (Mondays only--shared time with
the two AM 1330s in New York City). Since WHAZ dated back to 1922, just
about every station on 1330 had to protect it. As the closest co-channel
station, WCRB certainly had to do so. WCRB's pattern had nulls toward the
southwest (New York City) and northwest (roughly toward Troy). When WHAZ
became a daytimer, WCRB (actually, by then, WHET) had an opportunity to
improve its coverage by replacing the three-tower array with two taller
towers that produce a pattern with only a single null. This was done in 1976.

Despite the simplicity of the WRCA array, I gather that achieving a null
deep enough to protect the AM 1330 in New York (now WWRV) was no piece of
cake. I think the New York station must be protected all the way to its 2.5
mV/m groundwave contour at night, which is as much protection as any Class
III station ever received. I speculate that the top loading was done not
just to provide a better groundwave signal without running afoul of the
Waltham zoning, which apparently limits the height of towers at that site to
300', but also to reduce high-angle radiation. Since New York is only about
200 air miles from the site, the critical angle for skywave is quite high,
and the effect of the top load should be salutary. That's also why I dismiss
the idea of the back tower being electrically different from the front one.
If the towers were dissimilar, the vertical radiation pattern would be more
complex and less stable.

- -------------------------------
Dan Strassberg (Note: Address is CASE SENSITIVE!)
ALL _LOWER_ CASE!!!--> dan.strassberg@worldnet.att.net
(617) 558-4205; Fax (617) 928-4205