On Wed, 25 Mar 1998 09:01:22 +0000 Tom Rauch
<10eesfams2mi@mass1-pop.pmm.mci.net> writes:
To: <topband@contesting.com>
>> Date: Mon, 23 Mar 1998 22:20:23 -0900 (AKST)
>> From: Dan Robbins <kl7y@alaska.net>
>> Subject: Re: TopBand: From the bit bucket
>> To: topband@contesting.com
>
>An observation I also made and mentioned a while back. The ducts are
>nearly always over a mostly saltwater path.
And those ducts are fairly well established year after year as high as
10GHz. The W6 to KH6 path is an example and it is almost predictable.
Others exist along the East and West Coasts. Long established by at least
the ARRL as troposphere ducting, not to be confused with tropo scatter.
Tropo ducting is weather driven and very often highly selective in
frequency response and access points. My 12/24/92 ( Ithink that was the
date) 432MHz record was such an example of limited access. Stations only
a few miles to the East, North and West of me heard nothing of the
station down in Big Pine Key, FL. Stations along the route in the mid
Atlantic states heard nothing at all. Yet the record was established
with only 20W and 30W at the respective ends.
The ducts have been measured by many ham pilots in W6 land. They are
often only a few hundred feet tall and can be many miles in width. Some
have been reported to completely disappear a mile or two inland and under
100' in height differential. They take place over both all darkness and
all daylight paths but my experience has been predominantly darkness.
Coastal daylight paths here follow very close to grayline.
How this relates to 160M I do not know but I am not ready to discount
anything at this time. With El Nino causing so much weather disruption, I
still strongly feel that it should be considered a possible factor. I
will leave it up to the scientists to determine how much.
>> In the case of NL7Z/K1ZM, it could be that there was a common
>backscattering
>> area somewhere around, say, the HC8 area. This would be a mostly
>all water
>> path for both parties. The amount of signal backscattered on the
>lower freqs
>> can be very dependent upon the ocean state - smooth as glass and
>there is
>> very little backscatter, but if the swells are just right in
>direction,
>> spacing, amplitude, length, etc., then the back- or sidescatter can
>be
>> appreciable.
This will be the 3rd time I have asked....does anyone have weather maps
of this path available??
Since about half of SA was at the grayline during the VE1ZZ qso, and the
majority of the SA West Coast during W8JI's I will continue to wonder if
anyone in SA heard the contacts?
How about ZL, VK, etc ?
OTH radars can easily determine ocean wave velocity
>and some
>> kind of idea of the sea state thousands of miles away by the use of
>> backscattered signals. Given that the direct path between K1 and
>KL7 was
>> probably heavily absorbed, a backscatter path would certainly be
>feasible.
I have a few questions about OTH radar, excuse my ignorance.
What frequencies are generally used? Are they always spread spectrum?
Is the software programmed to ignore weather driven anamolies that could
be propagation enhancers?
And if not how does the radar differentiate between various scatter
modes, multipathing, etc and generate a true picture?
Since this is primarily...I thought... an air search radar, how accurate
is it at the surface, particularly right at a coastline? Or put another
way, could it even detect a coastal hugging duct in the presence of a
rugged coastline and very disturbed weather conditions?
Anyway it was my understanding that OTH was a true multihop driven animal
that knew exactly what areas it was looking at, adjusted frequency and
TOA as required and would not see what it was not looking for.
I have several other questions pending....
>
>It was observed by TWO of us here in GA, and I could hear my own
>dits echoing back when I beamed southwest. I pinged the SW, and got
>an echo. I pinged the NW, and there was none.
How far west into the USA was the skew path copied?
Next time consider usi
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ng a stopwatch or a scope Tom. That ping return
time could prove useful info. Good thinking BTW.
>
>Your analysis makes great sense when what I observed here is
>considered. The ducting stuff has never made sense, although I
>haven't ruled it out.
Nor have others, it "aint over until the fat lady sings".
>Since you are the one closest to having a true actual picture of
>paths, I have to " buy" your observations.
I feel that ALL of you have made a contribution, Tom, Dan, Bob, Yuri and
anyone else I have missed, and it would be premature to discount
anything until a LOT more work is done.
All of us should have a lot of respect for Dan's work but as Tom
frequently points out software has its limitations too. It would be nice
to know exactly what the software developers did and didnt do before it
all got shipped to Alaska for the operators to use.......but that is
probably rather secret info.
So we have 4 good subjects on the table now....elevated radials, delta
loops, antenna modeling software and propagation. That should give those
who only care about "heard last night" something more to complain about.
73 Carl KM1H
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