The 'shortwaving' effect has to do with the frequecy of the carrier being slightly "off" between the two transmitters. This is usually a few Hertz so you can actually hear the differences adding and subtracting. The more the carriers are off the faster the effect, until you actually start to hear a beat note or tone.
Carmine w1eqx
-----Original Message-----
From: lglavin@lycosmail.com
To: boston-radio-interest@bostonradio.org
Sent: 10/27/99 6:54 PM
Subject: Two WBZ's for the price of one
On those occasions when I've tuned to WBZ-AM just
before 8:00 am on my car radio while moving, I get
serious shortwaving for about two minutes. I deduce
that what's happening is that they turn on the 10K
stick behind the studio before turning off the 50K
blowtorch in Hull. Thus a moving vehicle is picking
up two wavefronts at the same time. This is not an
unusual experience for those of us in the Merrimack Valley. When I
worked at Wang, I would occasionally
tune to WLLH from its Lawrence signal as I left home
and then got the same shortwaving effect as I neared
Lowell. Now that's it's Spanish (and the volume
level seems really jacked up) I can't observe that
situation nowadays. A really strange instance of
two antennas causing RAPID back-and-forth changes in
volume occurred shortly after the new towers of what was
then WITS-AM 1510 were built. On one occasion, they
were testing the Waltham array with on-air programming
while the towers in North Quincy were still on pumping
out 50K north. This was with a stationary radio.
The fluttering was really fast; I don't know if this
had to do with its high frequency or the fact that
the more distant towers were aimed right at my location
while the closer ones were directed east as they are
now.
Laurence from Methuen
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