Re: [IRCA] max groundwave propagation distance

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> ``About the best you'll find in the US is a low frequency station getting
300
> miles ground wave.``

There's another side of this coin..

In 1961, RCA built the 990 station in Providence.  50kw, six tower array
concentrating the signal in a narrow beam aimed right at Providence.  Yet,
ground conductivity is so poor around here they couldn't get the required
25mv/m signal strength over their city of license.  Best they could do was
18mv/m.  They ended up getting a waiver for it.  The transmitter site is
maybe 20 miles or less out of town.  Top of the line engineering, equipment,
and financial support.  Results?  Poor, due entirely to conductivity.

That part of RI is very rocky with granite and other geological types.  Very
lossy.  From a DX perspective, it attenuates signals from that direction.
WGY-810 is very weak compared to NYC stations.  Vermont is nearly
non-existant.  That actually helps a fair bit when looking for TA and
Caribbean/South American stations.  Doesn't help when looking for Alaska or
Canadians.

The FCC has a chart showing default ground conductivities for the US, and
can be extrapolated out to the nearby Canadian areas.  Around here it's
shown as a .5 and that is about always proven very optimistic by
measurements.  Midwest is a 30 or so.  Makes a *huge* difference.  The
KFYR-550 up in the Dakotas at 5kw covers a big part of the area.  The 1kw on
550 here does cover well, but only in comparison to other locals.

Craig Healy
Providence, RI


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