WKOX night reception

[Dan.Strassberg]

Originally posted on the Radio-Info.com Boston board.

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Quote from: DanStrassberg on September 13, 2008, 02:47:10 pm

We'll have to see what the signal is like when they finally get to
operate at 50 kW. During the STA period. except when actual
prrof-of-performance measurements are being made, WKOX is restricted
to 10 kW-D and 1 kW-N--same powers as they used in Framingham.
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I stand by the above statement, BUT I heard something while listening
briefly to WKOX early this morning that may (or may not) be a bad omen
for the quality of nighttime reception once the station increases to
the full 50 kW-U. What I heard sounded like the dreaded "phasing"
phenomenon, which occurs when an AM station's high-angle skywave is
reflected back to earth within the normal nighttime groundwave
coverage area. The result is often referred to as a "short-wave"
effect--that is audio that becomes badly distorted for many seconds,
then clears up for a while only to become badly distorted again a few
seconds later. If you've ever heard recordings of short-wave
broadcasts from Europe or Africa during Word War II, you know what I'm
talking about. Those broadcasts were transmitted by short wave and
they have that characteristic sound.

On AM, the best way to minimize phasing is to use a half-wave
transmitting antenna, which minimizes high-angle skywave. At AM
frequencies, half-wave towers are tall and therefore are not liked by
neighbors or municipal authorities that have to grant building
permits. Half-wave towers also cost more to build and maintain than do
shorter ones. And since they are taller than 200', half-wave towers
for medium-wave stations must be illuminated, which adds to their
construction cost and requires paying ongoing electric bills for the
energy that keeps the lights on.

For all of these reasons, the WKOX/WRCA/WUNR five-tower site in Newton
uses towers just shorter than 200', which is less than 1/4 wavelength
at 1200. Electrically speaking, 85-degree towers are not at all
uncommon. Most likely, nearly half of the AM stations in the US use
towers that are no taller than 85 degrees. Signals from such towers
are not regarded as being subject to unusual phasing problems. But
that WKOX should possibly be experiencing bad phasing at a distance of
less than nine miles from its site and ~90 degrees away from its
radiation minimum is not a good early sign.

Once WKOX is running the full 50 kW, my location will be either just
inside or just outside of the station's 13.<something> mV/m NIF
contour. Normally, I don't think phasing should be expected to be a
significant problem at such a location. Right now, though, while WKOX
is running only 1 kW at night, the signal I get here is only about 1.8
mV/m. 1200 is a noisy channel here in the northeast and there
certainly is a lot of noise under WKOX's night signal. Could the
problem be the result of the interfering signals (CFGO, WTLA, WAGE,
and others)? Definitely! But it didn't sound to me as if that was the
case. I'll guess I'll just have to wait for the real (50 kW) thing.

However, nighttime-reception reports from others would be welcome.
Just be sure to tell us when and where you were listening.

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