Re: Things you can do on AM

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

At 03:29 PM 6/7/97 +0000, you wrote:
>
>> <snip> WEEI has a very good
>> signal now, it would have an even better one if it moved to Burlington.  
>
>
>Could 850's pattern work with the 680 array?  How'd they do that?
>
Quite possibly, but I don't know enough to say for sure. Turns out that the
line of the WEEI towers and the line of the WRKO towers are only 5 degrees
apart. If I recall, one set (I think WRKO's) is on an 80-degree line whereas
the other (WEEI's, I think) is on an 85 degree line. Since both sets of
towers are in line, each pattern is symmetrical about the line of the
towers. The WEEI towers are 120 degrees apart. The WRKO towers are further
apart in electrical degrees (136 degrees?--I can't recall the exact number).
To convert the spacing to degrees at 850, multiply by the reciprocal of the
frequency ratio, which for 680 and 850, works out to 1.25. So if I'm right
about 136 degrees at 680, the towers would be about 170 degrees apart at
850--very close to a half wavelength. That's a very wide spacing and I don't
know enough about designing directionals to be able to figure out if it
could work. The 590 towers are more than 1/2 wavelength apart, so the
spacing might work. As long as they can construct more towers, there's
obviously enough land to do the job. As for moving 1150 there, that would
definitely require more towers. No question that the 680 towers are too far
apart for 1150 and, at least for nighttime operation, they are also in the
wrong relative positions.

I don't know if three high-power directional stations share a single antenna
system anywhere, but I think it's technically feasible. I believe that four
10 kW nondirectional stations in Honolulu share an antenna. There are
several instances where two stations share a directional array. The AM 770
and the AM 1090 in Seattle (both 50 kW during the day) share a three-tower
array that was originally 1090's. In the metro New York area, WWDJ
Hackensack on 970 and WWRV New York on 1330 share what was originally 970's
directional. The array has three towers. Both stations are 5 kW and are
directional day and night using all three towers day and night. A few miles
to the south, WMCA New York on 570 and WNYC New York on 820 share what used
to be WMCA's three tower array. WMCA is 5 kW DA-1; WNYC is 10 kW-D/1 kW-N
DA-2. Both stations use all three towers day and night. And between these
two sites, WLIB 1190 is adding towers so it can begin nighttime operation
and WXLX 620 is constructing four more towers at the same site to move its
TX closer to New York. When the WLIB/WXLX site is complete, it will have
nine towers. WLIB will use three towers during the day and four towers at
night. WXLX will use five towers day and night. The two stations will share
one tower.

The WLIB/WXLX site is within a mile or so of a bunch of other high-power
stations--WOR, WEVD, WINS, WBBR, and now WWRL, which just increased its day
power to 25 kW. According to a consulting engineer I've talked with, the
problems of multiple stations sharing an antenna differ only in degree from
multiple stations with separate antenna systems in close proximity. In both
cases, you need traps to keep the towers from reradiating the other
stations' signals. The traps (filters) must be larger and more carefully
constructed if the stations are sharing a site, but the problem is
fundamentally the same. The worst problems arise when the stations are close
together in frequency. WINS and WEVD are 40 kHz apart. Both are 50 kW, and
though they don't share a site, the sites are quite close and WEVD is
directionalized toward the WINS site. This must be a fun problem. 

- -------------------------------
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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