WTIC night signal

[markwa1ion@aol.com]

The problem is that "somewhat close" to an AM station you are getting a 
combination of its groundwave and skywave.

Very close (on land within about 15 miles up around 1600 kHz, 40 miles 
down around 550; and at least triple those distances over seawater) the 
groundwave predominates.

Vertical antennas tend to put little signal straight up; furthermore, 
the ionosphere is a poorer reflector on high-angle incidence.  Near the 
station there is a "skip zone" where skywave is weak.  This is 
typically within about 60 miles.  Beyond that the take-off angle is 
lower so the antenna and ionosphere are both working more efficiently 
to provide a good bounced-back signal.

Strongest skip is typically at 150 to 500 miles from the transmitter.  
Much greater distance can be covered (including "longpath" - more than 
halfway around the world - in several documented cases).  But we're 
mainly concerned with entertainment-quality program listening here, not 
hardcore DX.

When you're in the 40 to 120 mile distance range on land, or somewhat 
greater on water, the groundwave and skywave signals can destructively 
interfere with each other, resulting in reception that is both inferior 
to what can be had 200+ miles out and, obviously, also to what can be 
had close to the transmitter.

If the skywave and groundwave signals stayed in phase with each other, 
this would not be a problem.  But, of course, they don't since the 
effective height of the ionospheric reflection point is always bouncing 
around.  Typically this would be at about 75 miles up but it can vary a 
lot, even within a matter of seconds.

Knowing this, it is entirely expected that WTIC would have a poorer 
night signal in the Berkshires of western MA than farther out in 
upstate NY, Ontario, etc.

Mark Connelly, WA1ION - Billerica, MA


<<
I've been out in the Finger Lakes region of NY recently and noticed I 
could hear the Sox on WTIC 1080 for most of the drive between there and 
Boston (along I-90), as long as it was after dark.

However, I also noticed that the skywave reception was VERY in-and-out 
for the entire drive...even the part of I-90 through Springfield, where 
one would think WTIC should come in just fine. But alas, not 
really...there's just as much static, hash and fade there as there is 
in  frickin' Syracuse.

I'm relatively new to AM DX'ing, but this strikes me as odd? Is there a 
particular reason why it'd come in at all so far away, but not improve 
even when so much closer?
--
--------------------------
Aaron Read
readaaron@friedbagels.com
Boston, MA 02446-2204
>>
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