From: floyd@polarnet.com (Floyd Davidson)
Newsgroups: uk.telecom,comp.dcom.telecom.tech
Subject: Re: Tropospheric Scattering
Date: 7 Sep 1996 01:58:39 GMT

clark@fsl.noaa.gov wrote:
>Jock Mackirdy wrote:
>> 
>> Simon Lord <simonl@hrmconsult.co.uk> wrote:
>> 
>> >Not sure what your definition of high power is Bill, but we used HF
>> >tropo on 2 watts power setting, using antennae slung in the trees about
>> >25 feet up, over ranges of >1000km, and my gonads are just fine!
>> 
>> The UK North Sea oilfield tropo scatter used ginormous parabolic
>> antennae whacking huge amounts of power into the troposphere. The
...
>I'm not sure what kind of comms the original poster was trying to
>accomplish but the U S Bureau of Reclamation operates a system of snow
>and water measurement gauges all over the mountainous western U S. It is
>called Snowtel or something like that and knowing the budget situation
>and approximate cost of the instrumentation this stuff has to be cheap.
>From the anecdotal reports I've heard from the folks who use the data it
>must be fairly effective. Since it is deployed in areas with no electric
>power available it was battery and solar powered so it had to be a low
>power unit. This system was deployed in the late 70s or early 80s.
>
>	The technical library at the National Institute of Standards and
>Technology (formerly National Bureau of Standards) has a reference:
>	call #: NTIA-R-83-116
>	author: Haakinson, E. J.
>	publisher: National Telecommunications Information Administration 
>	Title: Meteor Burst Communications Model  1983, 42 p

Note that UHF/Microwave Troposcatter and HF meteor burst are two
very very different things.

The meteor burst technique uses narrow band HF (the ones I've
worked on were in the 50 Mhz range) at moderate or even low power
levels to pass relatively low speed data using a store and forward
technique.  The signals are bounced off the ionized trails left by
meteors burning up in the earth's atmosphere, and commonly
encounter gaps of time when no path is available.  In addition to
remote rain/snow gauge measurements there were a number of such
installations used for radar data transmission in Alaska to backup
the regular satellite system communications facilities to various
remote Long Range Radar sites.  Those systems used multi-element
yagi antennas and output power in the 2-5 Kw range.  I'm not
directly familiar with the rain/snow gauge data systems though I
do know that the technology was (still is?) being used here in
Alaska too.  I'm sure that being solar powered they would use
relatively low power units, but since the amount of data to be
sent is very small the vastly longer gaps with no usable path
would be of no consequence.

By contrast the common 1000-2000Mhz troposcatter system involves a
baseband wide enough for at least 132 voice channels of telephone
quality circuits.  Commonly systems are arranged to use two
antennas for receiving and can provide either dual space
diversity, or quad diversity if both horizontally and vertically
polarized feed horns are used to feed separate receivers.  The
normal path suffers extreme fades which can last for variable
times from fractions of seconds to several seconds at worst, but
with diversity systems the combined signal from all receivers
rarely fades completely.  Of course everyone who has used a tropo
circuit much becomes familiar with the background "whoooshing"
sound of tropo fades!

Floyd

-- 
Floyd L. Davidson          Salcha, Alaska         floyd@tanana.polarnet.com

From: floyd@ptialaska.net (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Far Loss Echo??
Date: 8 Dec 1999 18:54:17 GMT

Art Jackson  <artjaxon@mindspring.com> wrote:
>Floyd Davidson wrote:
>> Hooda Gest <be@one_with.com> wrote:
>
>Speaking of Drive-In's, Floyd, when I first drove up to Pedro Dome,
>I wondered why they had a movie screen with the back of it to the
>parking lot. ;^) That was my first experience up close with a Tropo
>antenna. And Hooda must have been practicing up for his future
>telephone career, by putting into practice those telephone slogans,
>"Reach out and touch someone", and "Let your fingers do the walking".
>;^)

If he was, he was a lot cooler than most of us... ;-(

Speaking of tropo antennas at Pedro Dome, maybe everyone will
get a kick out of a story.  (Which I think I told here or in the
telecom groups once before, but its been awhile.)

Those 60 foot billboard antennas were indeed huge.  These things
were 75 feet high, with the 60 foot reflector sitting on a 15
foot high base.  And they were fed with some of the largest
waveguide ever used (this was in the frequency range of
700-1100Mhz, so the waveguide was like a foot or maybe a little
more across), with a feed horn mounted on a tower that stood up
in front of the billboard.  The feed horn had a huge "window",
for a feed horn anyway, in front.

Well in about 1986, long after the tropo system had been replaced,
all that was left at Pedro Dome of those old systems were piles
of bolts and some steel laying around where the billboards used
to be...  and two of those 45 foot towers for the feed horns.

Well one day when two of us were on the day shift, and the
evening shift fellow showed up, we did something a little
different.  (OK, maybe slightly like three 10 year old boys.)
We each had spent about 20 years on those sites by that time, so
this represents about 60 years of experience in the care and
feeding of these feed horns.  But the evening shift fellow had
just bought a 41 Mag pistol, and we all went out to his car to
take a look at it.  While we were admiring it, the owner
suddenly lit up with a really big grin, and said something to
the effect of "There is something I always wanted to do!"  We
followed him around back of the building.

We all, one after another, shot a hole in one of those goddamned
feedhorn windows up on the tower!  And we laughed like Hell and
went back inside.

[Pedro Dome is on top of a remote hill about 22 miles out of
Fairbanks, Alaska.  Discharging a firearm there was perfectly
legal.  The location is named in honor of Felix Pedro (Felicio
Pedroni, actually) who made the original gold disovery in the
Fairbanks district, in a small creek (Goldstream Creek) at the
base of the hill.  His discovery brought all the boomers from
Dawson, Yukon Territory to Alaska in 1902-4.  Today the largest
gold mine in Alaska, the Fort Knox Mine, operates in roughly the
same area, though it was only being explored in 1986.

  Floyd

--
Floyd L. Davidson                          floyd@barrow.com
Ukpeagvik (Barrow, Alaska)