Re: WNFT / WRKO / WEEI tower sites

[Dan Strassberg <dan.strassberg@worldnet.att.net>]

At 04:28 PM 6/17/97 +0000, you wrote:
>
>        The FCC database seems to show that the WEEI towers in Needham are
>extremely tall -- 57.5 percent of a wavelength. Taller than nearly any
>Class A station, even.

If the towers are as tall as the FCC database says, they are indeed taller
than those of most Class A stations, but the height is far from
unprecedented. The WBPS towers in Ashland were built for 1060, and when they
were used for 1060, they were almost as tall in terms of the
wavelength--205.5 degrees. I believe that a good ground system can at least
somewhat suppress the high-angle lobe that starts to appear as the tower
height increases beyond about 200 degrees. The WBPS ground system consists
of 240 radials per tower and they were 0.4 wavelength at 1060. The FCC
prescribes 120 1/4-wavelength radials, but many stations do quite well with
much shorter ground systems. Two Class IV stations I know of have towers
taller than 207 degrees: KVTO 1400 Berkeley CA has a true 225-degree tower.
KFRC 610 San Francisco diplexes from the KVTO tower, which is 97 degrees at
610. WSBC 1240 in Chicago has a 232-degree rooftop tower (and, curiously, a
signal strength per kW that, according to the database, is less than that of
WYPA 820, which diplexes from the same antenna structure--the tower is only
153 degrees at 820).

Also, have you noticed the note about mutual coupling in the database on
WEEI? One inference you might draw is that the towers are not physically 207
degrees high. I've seen the towers up close and they don't appear to be 665
ft tall. Scott Fybush also questions whether the database is correct on that
score. If you determine the antenna efficiency from the rms field given in
the database, it comes out to almost exactly 225 mV/m/kW unattenuated at one
mile, which suggests towers somewhat under 0.5 wavelength. However, I think
the efficiency number is bogus, as is WRKO's (which works out to almost
exactly 175 mV/m/kW). I think that back when those arrays were built,
consulting engineers inserted very conservative numbers so that they could
please the client when the measured performance exceeded what they had
predicted. However, I think that the appearance of the WEEI towers is
probably deceptive and that they really are as tall as the database says. I
base this on an article from the Needham Transcript, which Bob Bittner
showed me. Over a year ago, ARS was talking about replacing the WEEI towers
with a 1200' FM tower. Clearly ARS was already thinking of moving 850 to
Burlington. The article quoted an ARS exec as saying that if the company
decided to proceed with the construction, the three 600' towers currently on
the site would be removed.

>        This also brings to mind questions about these two antenna systems:
>Why are WRKO's towers so short?

They aren't so short. I forget the numbers now, but even the center tower is
over 1/4 wavelength, and at 850, they'd, in effect, be 25% taller. I doubt
that increasing the height of any but the center tower was ever a
possibility because of the site's proximity to Hanscom Field. The center
tower once was as tall as the other two. It was built to allow top mounting
of an FM pylon and, apparently, the old WLAW-FM 93.7 was up there. When the
FM went dark, they apparently removed the FM antenna and never bothered to
replace the section that had been removed. I asked WRKO's chief engineer
about this many years ago. His answer was "Why bother? The effect on the
signal would be negligible."

As for WEEI being better off at its current site, I'd bet a nice dinner that
you're dead wrong on that one. The WRKO site is just better, shorter towers
or no. Drive around eastern Mass and southern NH and listen. Although both
stations have very good signals, WRKO has the better signal in most places,
particularly southern NH and Cape Cod. The main reason is the location, but
WRKO's patterns are also more favorable. The better patterns are practical
because of the more favorable location, northwest of Boston. Although WEEI's
patterns are more spread out than a true cardioid (WBZ's pattern is very
close to a true cardioid; KTWO's is closer yet), WRKO's are more spread out
still. In fact, WRKO's day pattern is nulled slightly to the east to avoid
wasting signal over the ocean. The reason that WEEI's patterns aren't more
spread out is that, when the station was built (it went on the air from
Needham in 1947, by the way--long after NARBA, which took effect on March
29, 1941), AM's had to deliver 25 mV/m to the principal business district of
the COL. To do that from Needham on 850 required both the tall towers and
patterns that push a lot of signal to the east. By contrast, WRKO can
suppress radiation to the east somewhat and send its maximum signal to the
southeast, where it crosses through Boston and then proceeds to Cape Cod
over salt water. The signal in Chatham is damned near local. The northern
lobe, which is of equal intensity, covers the Merrimack Valley and southern
NH. Remember, the Burlington site is equidistant from downtown Boston and
Lawrence. WRKO puts a solid 25 mv/m into Lawrence and Lowell as well as
downtown Boston and everywhere in between.

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

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End of boston-radio-interest-digest V1 #71
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