DX...Skip and dead areas......questions

[Mark Connelly]

Skip zone is typically where groundwave reaches its outer limit of effectiveness (under 54 dBu / 0.5 mV/m) and skywave strength is not up to the full first-hop level typical of 200-600 miles.

Over poor soil characteristic of New England inland areas, the groundwave of even a 50 kW station tends to peter out in the 100 mile range low band and considerably less than that high band.

A vertical antenna puts less power up at the high angles more than 45 degrees off the horizon than lower down.  Also when the take-off angle is steep, the signal is more likely either to pass through the ionosphere about 75 miles up or be absorbed by it rather than cleanly bouncing back as a ray of light off a mirror would.

That's why a Boston signal that is fair in metro-west and gasping for air in Springfield is then boomingly-loud out around Utica and Rochester, NY.

In partial over-water situations where strong groundwave does extend out to 200 miles, such as some of the NYC stations here on Cape Cod, night reception sometimes gets complicated by the fact that skywave and groundwave are comparable strength and, as the phase relationship slides through the +/- 180 degree shift region, deep fades occur - worse than if on an all-land route where the groundwave would be an order of magnitude weaker than the skywave.

As far as the quality of WBZ reception in Schenectady versus WGY reception in Hull, it's "apples versus oranges."  WBZ is running a DA with gain and the first 7 miles westward over salt water.  WGY is omni and in a sandy pitch-pine belt like Plymouth, MA west of Rte. 3, a big attenuation pad.  No comparison.  WBZ wins.

Mark Connelly, WA1ION
South Yarmouth, MA   

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>From what I  understand, stations with big DX signals like the former clear

channels, maintain their groundwave/local signal at night...and as you move

away from that area there is a "dead zone" before the Skywave/Skip/DX signal

coverage begins.

WBZ claims a big signal at night...but if you drive due
west from Boston, 
you will find that after Worcester, WBZ's signal is
fluttering and 
unreliable.  But when you get to Albany it's pretty strong and
reliable.

Someone from this list (I think it was Martin Waters) was in CT,
and said he 
couldn't get a decent signal from WBZ day or night.  When I think
about it, 
WBZ has a lot of listeners in Mass, NH, and even RI...but not so
much in 
Vermont, W Mass, and CT.  Which is strange (to me anyway) for a
station that 
covers 38 states.

Here's the question:  Does the area of the
"dead zone" depend on the 
frequency of the station?  i.e....I mentioned that
WBZ (1030AM) is pretty 
reliable in Albany and Upstate NY.  However, WGY (810AM
(which is 
directional towards New England) is occaisionally listenable, but
not a 
reliable night signal.  You would think it would be pretty equal going
both 
ways.

Does the difference between 810 and 1030 alter the area of the
"dead zone" 
between ground wave and sky wave?

Thanks for your help...this
is something I've never understood fully.  ;-)

D
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