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[aprssig] WSPR for HF mobile?

Robert Bruninga bruninga at usna.edu
Wed Sep 29 12:57:02 UTC 2010


New APRS HF app?

This months AMRAD newsletter has an article by WA3LTJ about
using an extremely low-power HF protocol for HF beacons called
WSPR.  Apparently, using just 1 watt, you can be picked up by
their HF monitoring network that is linked to the internet just
like APRS.

See WSPRnet.org and click on the MAP tab and  you can see the
beacons being plotted live, several per minute.

I have not fully digested this topic, but as-is, it reports
position to the nearest 6 digit grid square (less than 3 miles
worst case)..  It hints at possible additional messages
contained in about 15 additional BITS.  If these are in addition
to the grid, then better position to a mile plus the existing
fixed APRS comments can be included.

W3PM already has it running on a small PIC processor apparently.

Again, if it transmits CALL, GRID and 15 more bits, then we have
APRS!  I'd use the 15 more bits as follows:

4 bits for SYMBOL
4 bits for comment (enroute, returning, ... Etc + customs)
3 bits better latitude (to 1/3rd mile)
4 bits better longitude

Again, I only quickly skimmed the article, and I could be all
wrong, but this sure looks like the long-haul world travelers
DREAM APRS app.

Transmissions take almost 2 minutes each.  At 1 watt, that is
120 watt-seconds.  Using 300 baud HF APRS takes 2 seconds and
with a 60 watt transmitter would use the same 120 watt seconds
of power.  But the savings is in not having to have a 60W amp,
and only needing a 1 watt transistor final stage.. Plus WSPR has
forward error correcting!

Anyway, something to look into.  See the map!  No reason why the
major APRS pages might not capture these same position reports
and put them on the APRS map?

I propose a standard SYMBOL when brought over to APRS...

1) give them an SSID of -12 (which we are using for all
non-standard "other system" entries into APRS.

2) Use the symbol code "WA" which is an overlay "W" on a box.

Am I missing anything? (probably)... Gotta get back to work!
QUESTION?  With FSK at 1.46 Hz separation, is doppler at 60 MPH
a problem?
Unless I calculate this wrong, at 20 meter band, moving at 60
MPH is about 1 Hz of doppler.  So maybe this can only be used
down at 80m or so where the dopper would be about 0.25 Hz?

Hummh...
Bob, Wb4APR




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