WKOX from the WUNR site

["Dan Strassberg" <Dan.Strassberg@worldnet.att.net>]

As I said in a post yesterday, when the details are revealed, I expect to
see that the plans call for the demolition of WUNR's two 350' towers and
their replacement by three shorter towers (just shy of 200' so they don't
require illumination). WKOX has proposed to use such towers in each of its
many applications for 50 kW-U. If that plan goes through, WUNR would then
diplex with WKOX from the new towers and would be granted higher--possibly
substantially higher--power.

However, WKOX has been rebuffed by local zoning authorities in each of its
previous attempts to find a new site--and ran into quite a few objections in
Framingham when it proposed demolishing its two 440' towers (the ones now
used by WMEX) and replacing them with three shorter unilluminated towers. So
why should the City of Newton behave any differently from the towns of
Framingham, Sudbury, and Wayland? I suspect that the WKOX proposal will
encounter difficulties in Newton also.

So I decided to look into what kind of facilities WKOX could get from the
two existing WUNR towers, or, if necessary, from two new towers of the same
height in the same locations as the present WUNR towers. (Even though the
WUNR towers are fairly recent-vintage replacements for the originals, it
might be necessary to replace them with ones that have larger base
insulators to accommodate a higher-powered station.)

Daytime operation with 50 kW would be a piece of cake, but I don't think 50
kW-N for WKOX is even a remote possibility from WUNR's array. However,
significantly more power than WKOX's current 1-kW night operation is
definitely possible. All of the stations that WKOX must protect are at
azimuths ranging from about 315 degrees to 190 degrees or so. WKOX's current
towers are on an azimuth of 35 degrees and the inverse-distance field that
WKOX delivers at night in the direction of CFGO in Ottawa (311 degrees)
exceeds 400 mV/m at 1 km. All of WKOX's applications and CPs for 50 kW-N
have proposed a line of three towers at an azimuth of 90 degrees. This 50-kW
operation would produce an estimated field toward CFGO of only 100 mV/m. The
most critical protection requirements are to WAGE in Leesburg VA and WOAI.
I'm not sure of the heading to WOAI, but it's pretty much the same as that
to WAGE. WAGE and WKOX were granted CPs to move to 1200 at the same time. I
believe that they were the first two grants on a former Class IA channel
when the FCC lifted its AM freeze around 1984. Currently, WKOX delivers
about 85 mV/m toward WAGE. The current CP for 50 kW increases this to
slightly more than 100 mV/m.

WUNR's towers are 78.75 degrees apart at 1200 (the spacing is almost
identical to that of WKOX's current towers in Framingham), but the WUNR
towers are at an azimuth of 70 degrees, 35 degrees clockwise with respect to
the WKOX towers. The neat thing is that this orientation is pretty well
centered at the middle of the range of azimuths of stations that WKOX must
protect. Were you to rotate WKOX's current night pattern clockwise by 35
degrees, the  radiation toward CFGO would be about 150 mV/m. Since the
field increases in proportion to the square root of the power, if you allow
for the lower efficiency of WUNR's 350' towers (approximately 153 degrees at
1200) vs that of WKOX's current 440' top-loaded towers (roughly 215 degrees
at 1200), WKOX could probably run about 10 kW at night from WUNR's towers
without increasing the groundwave radiated toward CFGO. The shorter towers
would radiate a slightly increased skywave, however, and at a distance of
500 km (the distance from Newton to Ottawa), the skywave is what counts in
determining interference.

However, WKOX's current pattern is nowhere near as tight as it could be. The
power into the south tower is only 80% of that into the north tower. The
WKOX pattern has two nulls, with a small lobe between them at 215 degrees.
By manipulating the ratio of the tower currents, the pattern can be
significantly tightened. By manipulating the phase relationship between the
tower currents, the two nulls can be moved apart or toward each other. The
limiting case is a single null along the axis of the towers. WAGE and WOAI
are almost directly on the axis of the WUNR array, suggesting that the
optimum phase might be roughly 101.25 degrees, which would produce a single
null at 250 degrees. I suspect, therefore, that a night power considerably
higher than 10 kW--maybe 20 kW--might be possible.

--

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