Re: [IRCA] [NRC-AM] Recent DXpedition to Grayland, WA & Florence, OR
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Re: [IRCA] [NRC-AM] Recent DXpedition to Grayland, WA & Florence, OR

Hi Nick,

<<<   But
there is an empirical gem in the second paper on page 917 concerning
cliff-side signals:  "...mesurements of the magnetic-field strength
due to Rome, 845kHz, at the top of Beachy Head (a vertical cliff in
southern England 160m high), gave results 2.3dB higher than values
measured on a beach well away from the cliff.  This enhanced filed
strength is believe to be a purely local effect, associated with the
sharpness of the cliff edge; 200m from the edge, the measured
increase was only 0.4dB.   These figures are consistent with the
theoretical increases in the magnetic and electric fields which occur
near the apex of a rectangular wedge illuminated by a plane
wave..."   Interestingly he goes on to say, similar to Bill's point
about Gary's "extreme DXing" prowess: "....severe practical
difficulties would attend the siting of an aerial so close to a cliff
edge."    (hi)   >>>


Thanks very much for that "empirical gem" from the Beachy Head study!
It seems that by accidentally setting up on the side of the Cape Perpetua sheer ocean side cliff with one of the small footprint FSL antennas, I was stumbling across this theoretical 2.3dB gain boost that the scientists had considered impractical to exploit. Some of the DU signals observed during the Cape Perpetua DXpedition seemed to border on science fiction, with even 765-Radio Kahungunu (2.5 kW) pegging the PL-380's S/N reading at 25. Apparently the development of the new FSL antenna will finally will allow DXers to tap into this ocean cliff propagation advantage (assuming that they don't first use up all their vacation $$$ by purchasing so many ferrite rods). 

73, Gary DeBock (in Puyallup, WA, USA)


-----Original Message-----
From: Nick Hall-Patch <nhp@xxxxxxxx>
To: Mailing list for the International Radio Club of America <irca@xxxxxxxxxxxxxxxx> 
Sent: Tue, Aug 7, 2012 9:46 pm
Subject: Re: [IRCA] [NRC-AM] Recent DXpedition to Grayland, WA & Florence, OR 


There are a couple of papers, one by Knight and Thoday "Influence of
the ground near transmitting and receiving aerials on the strength of
medium-frequency sky waves", Proceedings of IEE, Vol. 16, #6, June
1969, and "LF and MF Propagation: An Approximate Formula for
Estimating Sea Gain" by Knight, the BBC paper RD 1975/32.

A quick reread says 1000 feet shouldn't make too much difference at
least on land of the same elevation, if I've sailed past the
mathematics successfully, so my original point does not seem to be
backed up by theory, or (presumably) peer reviewed observation.   But
there is an empirical gem in the second paper on page 917 concerning
cliff-side signals:  "...mesurements of the magnetic-field strength
due to Rome, 845kHz, at the top of Beachy Head (a vertical cliff in
southern England 160m high), gave results 2.3dB higher than values
measured on a beach well away from the cliff.  This enhanced filed
strength is believe to be a purely local effect, associated with the
sharpness of the cliff edge; 200m from the edge, the measured
increase was only 0.4dB.   These figures are consistent with the
theoretical increases in the magnetic and electric fields which occur
near the apex of a rectangular wedge illuminated by a plane
wave..."   Interestingly he goes on to say, similar to Bill's point
about Gary's "extreme DXing" prowess: "....severe practical
difficulties would attend the siting of an aerial so close to a cliff
edge."    (hi)

best wishes,

Nick


At 22:11 07-08-12, you wrote:


On Aug 7, 2012, at 4:14 PM, Nick Hall-Patch wrote:
> I suspect that the Florence location suffered somewhat from being 
1000 feet

> inland, Gary and Bill.  My limited experience has been that
you're generally
> better off being right at the coast for the best DX, although
Gary's experience
> seems to point to an advantage to being right at the coast and
higher up, and
> that phenomenon certainly needs to be looked at more carefully.

That's almost what I blurted out in my original email -- what Gary
[and others' research to understand it] may have stumbled upon is
the true nature of 'sea gain' or 'coastal effect' and that it falls
off REALLY rapidly away from the coast whether you're at sea level or 
elevated.


I think it's really hard to 'compare' what Gary's able to hear on a
small portable radio with a super cool FSL antenna with what I do
via a Perseus & DKAZ.  Somehow I give him several 'bonus points'
just for doing what he does LIVE, with cars whoosing by and a few
hundred feet above the pounding surf while I'm literally
sleeping!  Now that I've been to where Gary did his last DXpedition
I'm VERY impressed.  I would not do what he does.

I might visit Sea Lion Caves down the road but I would NOT stand out
there with a portable radio and a FSL and cars whooshing by at
sunrise!  For that alone he deserves a '10' on the Olympics scale.

> There was a research paper done years ago by the BBC, I believe,
showing the
> "coastal effect" as a wavefront moved from the water to the land,
and although
> there were peaks in signal strength as one moved inland, their
location depended
> on the frequency of the received signal, were compensated for
by  lower signal
> strength in the area between the peaks, and, overall signal
strength dropped the
> further inland one went.   I'll look it up again when I'm home; I
have a vague
> recollection that cliffs might have been incidentally involved,
though I don't
> think that clifftop vs. seashore was investigated.

I've seen that paper and know some people who had something to do
with it ... assuming they're still alive.  It was incorporated, in
some fashion, into the Rio 1979 Final Acts where the Region 1 & 3 MW
stuff was negotiated/allocated.  I remember once writing a TI-59
'program' to calculate desired and undesired signals along radials
using the 'Rio Plan.'  Had to see if changes we wanted to make to
VOA MW facilities would affect Rss by more than 0.5 dB -- the limit
to having other admins notified!

Blah, blah, blah ... that's when people still gave a hoot about AM
and HF.  :-(
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