750 CP's

[Dan.Strassberg]

WJIB is a US Class D AM on a Canadian Class A channel. There are many
such stations, but as a group, they constitute a special class as a
result of stations of all classes in North America (I think this
applies to FMs as well as AMs) now receiving protection within their
normally protected contours only over land that lies within their
national borders. The reason these US Class Ds can now operate at
night, albeit in most cases with very low power, whereas they
previously had to sign off at local sunset, is that Class A AMs used
to receive protection within their 0.5 mV/m 50% skywave contours even
when those contours extended into areas outside the Class As' national
borders.

The Toronto Class A (CFZM? ex-CBL) delivers a 0.5 mV/m 50% skywave
signal hundreds of miles to the southwest of Boston. That's the
contour that would receive protection of it were in Canada. As it is,
the contour covers many thousands of square miles of US land where it
no longer has to receive protection. However, WJIB must protect the
point of land where this contour intersects the Canada/US border.
Thus, WJIB could, indeed, increase its night power quite substantially
if Bob wanted to spend millions of dollars to install a sufficiently
complex directional antenna--assuming he could find land on which to
construct it.

In theory, WJIB could run perhaps 50W at night (give or take) if Bob
wanted to pay rent to American Tower systems to use its towers at the
WWDJ/WAZN site in Lexington. A two-tower array for 740 that protected
the Canada/US border could be constructed using the tall (FM) tower
and one of the AM towers. That array could limit the signal toward
Canada to the equivalent of 5W ND over a substantial arc while
delivering the equivalent of perhaps 80W ND over Belmont and parts of
Watertown and Cambridge. Since WJIB would still be restricted to using
much less than 250W at night, it would remain a Class D, meaning that
it would not have to deliver an NIF signal to any of its CoL,
Cambridge--and it probably wouldn't do so. But the densly populated
area within a mile or so of the WJIB tower that currently receives
pretty good signal at night would no longer do so because the
transmitter would have moved further away.

And it would be an expensive project. The FM tower would have to be
skirted; it is a grounded-base tower, so a so-called Folded Unipole AM
antenna would have to be installed on it and a ground system would
have to be installed around the tower base. The expense and the
problems don't stop there, though. Two stations, WWDJ and WAZN,
already use the site, so the filtering problems would be quite
complex. And the site is only a couple of miles from 50-kW WWZN.
Filtering that enormous signal would be a huge headache. And remember,
the second harmonic of 740 is 1480, only 10 kHz from WAZN. I hope
that anyone who thinks this project might be practical knows how to
pronounce engineering nightmare.

-----
Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: "Sid Schweiger" <sid@wrko.com>
To: <bri@bostonradio.org>
Sent: Thursday, June 04, 2009 2:34 PM
Subject: RE: 750 CP's


>>it sounds like this applies to every station
indiscriminately.  Apparently WJIB, with its 5-watt nighttime signal,
can't make any transmitter upgrades without degrading its night
signal.  Nor can WBZ, with its 50,000 watts clear-channel.  Does this
really make sense?<<

WJIB would certainly be able to show the Friendly Cookie Company that
ratcheting back its nighttime signal would have close to zero effect
on any other co- or adjacent-channel signal.  I can't say if a waiver
of the ratcheting policy has ever been granted, but that doesn't mean
they couldn't try.  Waivers are granted at the FCC for all kinds of
reasons.

Sid Schweiger
IT Manager, Entercom New England
20 Guest St / 3d Floor
Brighton MA  02135-2040