I'll just stick in a few responses to others' comments about what I
wrote on the 'beach' thread and then I'll get out of the way.
<<
It is tricky to use receiving tests to gauge the
effectiveness of proposed transmitting antennas
for two reasons. You are probably listening on
receiving type antennas rather than transmitting
antennas. In that case, you have only shown that
receiving antennas work better over salt water.
Definitely, as I'd mentioned, less site-to-site variability would be
shown with a full-size efficient transmitting type antenna, whether a
vertical over a good ground system or a high (>150 ft. elevation)
horizontal dipole / yagi.
Smaller receiving loops and active whips exhibit the greatest influence
due to surrounding ground conductivity and elevation profiles. This is
particularly the case on groundwave or very low angle skip. High angle
skip is largely unaffected by the nature of the surrounding landscape;
certainly by the time you get to Near Vertical Incidence, that can work
even if you are surrounded by tall buildings or mountains.
As some of the propagation paths we desire do involve things such as
the ability to "open" the band pre-sunset on the US/Canada East Coast
to incoming Europeans, skip propagation at very low angles is a matter
of interest. If sunset is at 4 p.m. EST (2100 UTC) in December in
MA/ME, for instance, the ability to work Europeans as much as three
hours earlier than that is going to be more likely at a shore site for
a given transmitter/receiver/antenna configuration. For such early
QSO's inland I think a mountain top (and a heck of a lot of buried
copper) would be needed. By an hour or so after sunset, the shore
versus inland differences would reduce to barely perceptible as the
optimum take-off angle would be considerably higher above the horizon.
Still, having potentially two or more hours of useful communication at
the start of an opening going east or the end of an opening going west
is still not a trivial matter, especially in a contest scenario when
every added QSO point matters.
Extrapolating groundwave results from a proper-size broadcast vertical
with radials exhibits that coverage even from a professional-grade
antenna is affected greatly by surrounding ground conductivity.
Keeping in mind that the following map for WOND 1400 (near Atlantic
City, NJ) shows a pattern from a single-tower non-directional antenna,
it's quite obvious that sea gain is for real:
http://www.radio-locator.com/cgi-bin/pat?call=WOND&service=AM&status=L&hours=U
This station is easy daytime copy here on Cape Cod at over 250 miles.
Going inland to the northwest of the tower, WOND has less strength at a
mere 30 miles.
Reciprocity would mean that the same tower used as a receiving antenna
would have a similar pick-up pattern: far better sensitivity going east
than west. This jibes quite well with what is observed routinely at
seashore broadcast-band DXpeditions even when talking about afternoon
low-angle skip from Europe, the Middle East, Africa, and Brazil.
<<
Second, are these comparisons based on S meter readings
or signal to noise ratio? If the latter, then it
could just as well be that it is very quiet on the
shore because nothing is out there. Especially if
you use directional antennas to listen.
S-meter readings. Northeastern Brazil stations (Fortaleza / Natal /
Recife areas) and "deep" Africans (e.g. the former BBC Lesotho on 1197
kHz) that could routinely hit S-9 on the Drake R8A or Perseus with car
roof loop at shore sites in Rockport, MA and Orleans, MA were, at best,
in the S-2 category (or more likely just non-existent) with the same
mobile set-up at my former location in Billerica, MA (15 miles
northwest of Boston; 15-25 miles inland on bearings of interest).
Differences on western Europe (e.g. Absolute Radio UK 1215), especially
after sunset, were a good deal less as the skip was at a high enough
angle to be less "groundwave-like."
I believe that Nick Hall-Patch and others have done simultaneous inland
versus coastal signal observations of Asian and Down Under signals
received around dawn in BC, WA, and OR on a fairly regular basis. I
think that, for them, coastal beats inland most of the time on both
actual signal strength as well as signal-to-noise /
signal-to-interfering stations metrics.
Once in a while greyline does give you one of those "high angle is
best" tilted-layer paths and the best location winds up being the one
under the spotlight. In that case, coastal versus inland becomes
largely irrelevant.
<<
BTW, what are the best California BC stations to look for? Its been
decades
since Ive heard one but I havent tried hard at all.
Carl
KM1H
KNX on 1070 is about the only California station that has a ghost of a
chance to make it to New England now that the former clear channels are
plugged up with so many domestic and Cuban stations. Try just before
dawn. A properly-aimed Beverage will help. 640 KFI and 680 KNBR used
to make the trip east in the '60s/'70s when many US stations went off
the air after midnight. Those days are gone. The 1070 situation
actually improved when CBA New Brunswick went silent about 10 years ago.
West Coast AM broadcast stations are actually heard more often in
Scandinavia (over the pole) than on the US East Coast.
<<
ENOUGH of the "...modeling the proverbial 'vertical on the beach'"
already...!
My "delete" button is beginning to wear out.
<<
I swear I am going to start a self serving thread called ? vertical
near by to a
beach.??
<<
Yeah!! -This one's been "done to death'!
I receive the postings in digest form so I guess that means I have to
hit delete less often if at all.
I suppose I was under the mistaken notion that antenna and propagation
discussions were a legitimate topic here.
Mark Connelly, WA1ION
South Yarmouth, MA
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