I am far from technical on the subject, but I can agree with the
dampening
effect. I went up to Don Kaskey's house a few times and we listened
on car
radio and on my Grundig at the beach in San Francisco. I drove the
Great
Highway south after leaving and had strong signals on several TP
frequencies. When I turned inland, the signals dropped off
dramatically.
Many were gone by the time I was 3 miles inland, though the stronger
ones
lasted until I was 10 miles in, and the strongest continued on.
One night in 1980/1981, I went out to an artichoke patch (I
think...it was
dark and rainy) north of Santa Cruz with Doug Nyholm (remember him?)
and we
strung out 1200-1300 foot of longwire on stakes attached to his
Yaesu. We
had reasonable audio on 30-35 TPs from Australia/New Zealand/Fiji. I
had
never heard most of them before or after that night.
There have been some good exceptions to the rule though...I used to
pull in
a AM station from Malaysia with some regularity when I lived in
Manteca CA,
which is politely referred to as the armpit of California. I also had
armchair quality on a Central Chinese station on 1525 kHz way back when.
Mike Hawkins
On Mon, May 3, 2010 at 10:46 PM, Nick Hall-Patch <nhp@xxxxxxxx> wrote:
At 23:04 5/3/2010, you wrote:
Those would indeed be great, and away from all forms of RF noise.
I was also wondering how close they were to the ocean; my
understanding is
that going even a few hundred yards or so inland puts a significant
damper
on TA/TP signals - can any TA/TP veterans confirm/correct this?
Hi Kevin,
I suspect that the amount of loss is somewhat dependent on the ground
conductivity of the inshore land, the frequency of the signal, and the
arrival angle of the signals, but only really have data for the
second of
those suppositions. The others are based on the supposition that a low
arrival angle signal from over the ocean will lose strength more
slowly over
highly conductive land (salt marsh) compared with poorly conductive
land
(rock) the further it travels. A high arrival angle signal, on the
other
hand, presumably will not be as affected by ground conductivity so
one might
assume it will be nearly as strong inland as at the shore.
As for the second supposition, a few years ago, John Bryant and I
did some
simultaneous signal strength recordings at the shore and points up
to around
two kilometers inland at Grayland, and found that the loss was
highest for
higher frequency signals, and varied from 1 to 12 dB depending on
how far
inland one was (but signals were almost always best right at the
beach).
It didn't seem to be a linear decay, rather there seemed to be
reinforcements and cancellations of signals at different points, so
one
might luck out and hit a "pretty good" spot further inland, so one
shouldn't
out of hand reject a site a little ways inland. Randy Seaver wrote
a good
article years ago about this, entitled "Sea Gain" which is IRCA
reprint
T062, and some of our results did seem to have some theoretical
underpinnings (Randy had found some academic work on the subject).
Unfortunately, both John and I were pretty busy at the time, and never
really finalized any conclusions on the subje!
ct...."more study is needed" (I'm sure Mike of the Grayland motel
would
be OK with several weeks of rental from DX researchers.....).
best wishes,
Nick
*****************************
Nick Hall-Patch
Victoria, BC
Canada
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