[aprssig] YOTREPS and AIS

Dave Skolnick dskolnick at gmail.com
Fri Aug 1 08:45:12 EDT 2008

> From: "Robert Bruninga" <bruninga at usna.edu>
>>> Seems like HF APRS would be a more efficient way
>>> to send position reports than sending text files
>>> through Winlink...
>> For a sailing vessel with power conservation
>> concerns there is a lot of appeal to... PACTOR
>> that acknowledges receipt...
> What we have always needed in this case is something that powers
> up the HF rig only to send the APRS posit

It occurred to me after I posted that there are times the radio is on
for extended periods. Many of us do use the same SSB - PACTOR modem -
laptop combination to receive weather fax. If SCS could be convinced
to add APRS to their firmware and Airmail included a background task
to transmit periodically (on a not-to-conflict basis with e-mail,
wxfax, and NAVTEX) it could be done.

Actually it would be nice if the schedule-file-driven capability in
Airmail was able to switch power to the radio. That would be a nice
power saver.

> The TX power even at 100 watts is quite insignificant to
> the RX power of a typical transceiver.

You have that right. My battery bank is about 8100 watt-hours. To
maximize battery life, one doesn't draw the bank below 50% capacity;
since charge acceptance rolls off dramatically as batteries are
charged it is rarely charged above 80% at sea. That gives me roughly
2400 watt-hours between charge cycles for refrigeration,
communications, navigation instruments, navigation and convenience
lighting, and other miscellaneous consumption. You learn to watch
every erg. Living off-the-grid takes some adjustment.

At the moment I feel rich with 60 A shore-power and community wifi! <grin>

> My HF.TXT file (or is it BOATS.TXT?) has asked for someone to
> build a single Xtal HF TX since about 1993.

A very interesting idea, especially if a little controller could make
it completely stand-alone.

Unfortunately that APRS solution would be difficult to use on most
boats since antenna are in short supply. My HF antenna is an insulated
section of the backstay (part of the rigging that holds up the mast)
fed from a tuner. It isn't practical to switch it between radios and
it would be awkward (and expensive) to try to insulate another piece
of rigging for another antenna. That is typical of most sailboats.

The VHF satellite idea is interesting. I already squeezed in a
dual-band 2m/440 vertical and have been looking at a quadrifilar
antenna for 139 MHz satellite weather imagery. I'll have to give that
some thought and research. What's one more piece of gear jammed into
my nav-station? <grin>

sail fast, dave / KO4MI
S/V Auspicious

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