Whence the nighttime interference on 1030?
Thu Feb 14 15:18:46 EST 2019
The most likely cause of interference to WBZ is WBZ itself. There are two
types of emissions from AM stations: a surface wave, which follows the
ground, and a sky wave, which follows a straight line into the atmosphere.
When it hits the "D" layer of the ionosphere it is absorbed and
However, the "D" layer is only present during the day. At night it
disappears, and the sky wave continues until it hits the "E" or "F" layers
of the ionosphere, which reflect it downward. That is why people hundreds
or even thousands of miles away can hear WBZ at night, but not during the
WBZ's surface-wave coverage is very impressive; driving to visit my father
in upstate NY a few years ago, I had a listenable signal from WBZ all the
way to Schenevus, NY, on I-88 just short of Oneonta. That's about 150
miles, all of it over land -- excellent for an AM staion in daytime.
If you live at the outer edge of WBZ's daytime coverage area, you will
often receive both the surface wave and the reflected sky wave, and they
will interfere with each other. In the worst case they can completely
cancel. If they do, you'll hear anything else that happens to be on 1030
but not WBZ.
On Wed, 13 Feb 2019, Doug Drown wrote:
> I live on the upper midcoast of Maine, where WBZ's daytime signal comes in
> like gang busters --- absolutely crystal clear, no hiss or interference, as
> though the transmitter were just down the road. One the sun sets, however,
> it deteriorates rapidly, especially at this time of year. What is/are the
> station(s) I'm hearing on 1030 kHz? They seem to interfere with one
> another, such that I can't make anything out plainly. Am I correct in
> thinking that 'BZ's signal is nondirectional? If so, the presence of these
> other stations' signals surprises me.
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