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Re: Tower lighting

A goodly percentage of four-tower arrays are either rectangles or
parallelograms. In many such cases, the spacing along one axis is roughly 90
degrees whereas the spacing along the other axis is roughly 180 degrees.
Such a four-tower array is a classic "multiplication-method" design. If you
take either pair of towers that are 180 degrees apart, those two towers, by
themseleves, if fed equal power in-phase, would produce a figure-eight
pattern with its major axis perpendicular to the line between the towers. If
you also feed equal powers (same magnitude as you used for the first pair)
in phase to the second 180-degree pair but make the phase 90 degrees from
that of the first pair, you get a unidirectional, fairly narrow pattern
whose maximum radiation lies along the line that joins either 90-degree
pair. This happens because the unidirectional cardioid patterns that either
90-degree pair would produce are multiplied by the figure-eight patterns
that either 180-degree pair would produce. So if the far-apart pairs in
PJB's array are 180 degrees apart along an east-west line and the
close-together pairs are 90 degrees apart along a north-south line, it could
be that the array was designed to send maximum radiation either to the north
or the south. Moreover, the array could be designed so that when the station
chooses, it can change patterns to send the signal in one of those two
directions but not in the other, enabling separate sevices to the US and
South America at different times--all the while protecting the Mexican 800
in Ciudad Juarez. Moreover, by using either one of the 180-degree pairs by
itself, PJB could serve both the US and South America simultaneously.

A number of six-tower arrays use an extension of this approach. If you place
three towers in a line, space them 180-degrees apart, and feed power to them
in phase in a 1:2:1 ratio, you get a narrower figure-eight pattern than you
do with just two towers 180 degrees apart fed equal powers in phase. Now add
a second line of towers with the same spacing and place this second line 90
degrees from the first line. Feed the towers in this line powers equal to
what you feed their closest neighbors in the first line, but make the phase
of the current you feed to the second line 90 degrees with respect to the
current you feed to the corresponding towers in the first line. Now you get
a very narrow unidirectional pattern parallel to the lines between the
90-degree-spaced pairs.

All sorts of variations are possible. the 90-degree-spaced pairs do not have
to be (and usually aren't) at right angles to the 180-degree-spaced pairs.
The "180" and "90" degree spacing don't have to be (and usually aren't)
precisely 180 and 90 degrees. The current ratios in the two 180-degree lines
don't have to be (and usually aren't) exactly equal. And so on. So it's
quite possible to "tweak" these designs.


Dan Strassberg, dan.strassberg@worldnet.att.net
Phone: 1-617-558-4205, eFax: 1-707-215-6367

-----Original Message-----
From: EM1 GITCHIER <RGITSCHIER@doyle.navy.mil>
To: boston-radio-interest@bostonradio.org
Date: Sunday, April 23, 2000 1:18 PM
Subject: Tower lighting

>> As our exteemed list partner the Good Mr. Bittner pointed out to me, yes
>> indeed, the four towers of PJB 800khz, Trans World Radio form a
>> The distances between the east-west-erly tower azimuths seem to be
>> spaced as compared to the pair of towers on a North-South-erly direction
>> (undoubtedtly a descriptive faux-pax due to too much island cheer or
>> massive
>> dosage of RF...). Just verified that for myself via a moonlit bike hike
>> down
>> to the southern tip of the island to the site. Unfortunately, no one was
>> manning the station, just a gate guard and power plant operator was there
>> to
>> greet me. My clue should of been no one was answering the phone...  ahh,
>> automation. What happened to the good old days with engineers handcuffed
>> to
>> the transmitter cabinets? They're long gone, chum, long gone....
>> Now l'm going to go outside the ship and see if I can pull in the mighty
>> 800
>> WCCM once I figure how to null this powerhouse from about 7 to 10 miles
>> away. lol....
>> Incidentially, about 20% or so of their beacon lights are extinguished.
>> BTW, not
>> a single strobe was seen on the Island of Bonaire tonight...
>> Ron Gitschier
>> Bonaire, N.A.