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[IRCA] Max. Groundwave Propagation Distance?
Jeff,
That's a tough one to summarize quickly. Yes on of the factors is
frequency, the lower on the dial the better
but more importantly the conductivity of the soil.
The FCC years ago published a conductivity map for the US which you can
download on their website.
It ranges for .5 to 30 over land. Long Island and around Atlanta have some
of the worst conductivity. Parts of the midwest and Texas are at or near 30.
As a rule of thumb you occasionally find an area that matches the map but
for the most part signal strength measurements show the conductivity is a lot
less. Most of Dallas for example is in a 30 but in reality is about a four
to a seven.
The real champ is the ocean rated at 5000. A good example, Radio Vision
Christiana in the Turks and Caicos on 530 can be heard along Florida's east
coast during the day as far north as St. Augustine, well over 700 miles thanks
to the great conductivity. I have personally listened during midday to
WMEN/640 from Royal Palm Beach, Fla in the Dominican Republic several times which
is pushing 800 miles. About the best you'll find in the US is a low frequency
station getting 300 miles ground wave.
The more hills in the terrain the worst the conductivity, flat pasture land
with fertile soil is the best, an exception being the Florida Everglades,
rated at an eight but more like a 15 due to the swampy soil.
Sand makes a lousy conductor as illustrated by the coastal area from New
York to Florida.
Where I live we are in a 15 but a few miles north it's an eight and a few
miles west it goes down to a four as you head towards the mountains.
The changes come gradually from one conductivity to another.
Jerry Kiefer
Roswell, NM
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