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[aprssig] WSPR for HF mobile?

Jon K Hellan hellan at acm.org
Wed Sep 29 13:28:32 UTC 2010


Lynn W. Deffenbaugh (Mr) wrote:
> I may be wrong, but IIRC when I played with WSPR monitoring a few months
> ago you must have an rock solid accurate time signal. This could be
> quite a challenge for the ultra-mobile traveler.  I'm thinking it was
> sub-second synchronization to standard was required.

A timing grade GPS, e.g. a Garmin GPS 18 with serial port, is $ 82 on ebay. Its pulse per second output will
have nanosecond precision (if you have a good view of the sky, leave it stationary and account for cable lengths).
Preserving that precision in your own electronics can be a challenge. A general purpose PC running Linux or BSD
can be disciplined to better than 10 microseconds, specialized hardware will do a lot better. A USB GPS will do
much worse.

See the archives of the time-nuts mailing list for details, and John Ackermann N8UR's site www.febo.com.

A HF setup is so bulky that time synch won't be a showstopper.

Jon LA4RT, Trondheim, Norway

> Lynn (D) - KJ4ERJ - Tinkerer in digital modes...
> 
> Robert Bruninga wrote:
>> 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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