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[aprssig] Re: RS on expedition, but non ham?

Ray McKnight shortsheep at worldnet.att.net
Tue Nov 2 00:52:49 UTC 2004


Well, I say from experience that I'm fairly certain at 80 deg N you won't be
within the footprint of *any* commercial geostationary satellites.  Taking
Inmarsat-East as an example, coverage stops at about 77 degrees.  At this
point, the large (2.5-3 meter dish) is at the lower stop limitation,
basically zero elevation or as close as the mount will allow, and your only
catching enough signal from the beamwidth of the antenna to get into the
bird marginally.  If other satellites in geostationary orbits are in orbits
similar to the Inmarsat's, they exhibit a small wobble in their orbit, shown
as a slight "wandering" of about 1.5 degrees if I recall correctly, from
center, sort of like a drunk wandering across the centerline, twice a day.
So at 77, we'd have only periodic access, and losing the bird when it was on
it meandered on the southern wobble.  Note that because the antenna was at
zero elevation, absolutely anything higher than sea level would block the
signal.  I guess some sat's are probably in slightly higher orbits but
traveling a little faster to compensate?  And thus may have a slightly
larger footprint, but remember, these things are operated by beancounters,
and it doesn't pay to spend the extra $$ to loft a bird high enough to
achieve a larger footprint than this, because only a small handful of ships
can navigate in Artic/Antarctic waters, the population above the arctic
circle is diminishingly less the farther N/S you go, and they aren't all
that many people who vacation or conduct science there. LEO's are the only
game in town, and now that the Iridium constellation is back online, one of
the few reliable and viable solutions for comm's (backpacking friendly) in
these regions.

As far as HF, you're gonna have some big difficulties.  First, even a low
power rig needs a lot of juice to keep it running, so battery life is a
definite factor.  The only 2 ways to get it are wind or solar.  Maybe
they'll have enough room to carry a small wind generator to set up when they
make camp.  If they're going to rely on solar, well, if you've never been
north of the Artic Circle, sunlight isn't like anything you've ever seen.
Sure, in the summer it never sets, but it's very low on the horizon, and
thus solar cells aren't all that effective.  There's usually haze or fog the
contend with as well.

HF itself in the Arctic is very difficult.  Signals exhibit flutter which
probably preclude low power from being effective.  I traveled from
Newfoundland up to 77N in Baffin Bay, Thule, poked our nose in the Northwest
Passage, then all along the western coast of Greenland, *THROUGH* Greenland
(in a channel only navigated a couple of other times because it's almost
completely icebound), over to Iceland, then Ireland.  I was able to maintain
nearly continual Pactor-II comms with a shore station in Alameda, CA.  But
They had a huge log-periodic and about 5 KW aimed at use, and I had a 50ft
tall whip with a kilowatt.  Much of the time their signal was only barely
above the noise.  Sometimes it was inaudible, but keep in mind that
Pactor-II can maintain comms down to -18db BELOW the noise floor.  I think
in Ireland we stretched the envelope of the maximum Pactor path, which I
believe is quoted at around 8,000 mi due to timing delays in propagation.
But you need a decent radio, a simple QRP rig isn't stable enough, if you
drift more than a few hundred cycles you can be in trouble.

Is ISS's orbit high enough to provide a footprint at 80 degrees over Russia?
I still say they should look into Service Argos.  With something like 300mw
into a 1-ft whip you'll get any data you want into the bird about 5 or so
times a day.  The only two drawbacks I see is that you need to chirp
continuously because you can't really do pass predictions very easily on an
expedition like this (they could easily schedule only 1 or 2 transmit
periods a day, but I don't think this would offer a cost savings, but would
prolong battery life).  But several companies make transponders used in
ocean drifting buoys that can last for over a year, due to the low power of
the TX, no display or control interface, or the "power overhead" of a
conventional transceiver.  They're also VERY rugged and reliable.  You'd
just need to figure out how to interface to it, probably a fairly trivial
matter.  The other drawback is the cost of Argos service, but we're not
talking about a year-long expedition here, so that's probably well within
reason.

-----Original Message-----
From: aprssig-bounces at lists.tapr.org [mailto:aprssig-bounces at lists.tapr.org]
On Behalf Of Scott Miller
Sent: Monday, November 01, 2004 10:57
To: TAPR APRS Mailing List
Subject: Re: [aprssig] Re: RS on expedition, but non ham?

> Equipment contributed/run by a US amateur would really not be appropriate
> unless they were physically ON the expedition, even assuming it might be
> legal for them to supply.

I'm offering to contribute the encoder hardware, not radio gear.  As far as
legal operation of a transmitter, I think having a member of the expedition
get a license would be the safest way to go.  I have no idea what Russian
law says about automated beacons.

> communications. Playing with satellite transmissions using ham equipment
> *probably* will not be as reliable and compact, even if you had a trained
> operator on the expedition.

At 80 degrees North, you're probably not going to hit many equatorial birds
or ISS, so your options are going to be pretty limited.

I still think an HF QRP rig would be the way to go, if you could set up an
appropriate antenna.  I'm not an expert on HF propagation or antennas,
though.  What's an appropriate band for QRP at the pole, and what's a good
antenna for a sled?

Scott, N1VG
http://n1vg.net/opentracker


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