[aprssig] yotreps and ais

[jimlux]

> ------------------------------
> 
> Message: 4
> Date: Thu, 31 Jul 2008 10:49:56 -0400
> From: "Robert Bruninga" <bruninga at usna.edu>
> Subject: Re: [aprssig] YOTREPS and AIS
> To: "'TAPR APRS Mailing List'" <aprssig at lists.tapr.org>
> Message-ID: <5CC69E9D511C49B991EB05A049853C87 at ewlab.usna.edu>
> Content-Type: text/plain;	charset="us-ascii"
> 
>>> 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, and then powers back
> down.  The TX power even at 100 watts is quite insignificant to
> the RX power of a typical transceiver.  RX power is about 12
> Watt-Hours per hour (for a 1 amp rig) compared to 1 Watt-hour
> per hour for the TX running one posit every 10 minutes.
> 
> My HF.TXT file (or is it BOATS.TXT?) has asked for someone to
> build a single Xtal HF TX since about 1993.  It could be built
> using only about 6 transistors and some power MOSFETS and
> producce 50 Watts (for 3 seconds every 10 minutes) on the 10 MHz
> frequency and fit inside a brick no larger than an HT.  The
> problem has always been getting frequency stability down to 10
> Hz or less.  And that *ain't* easy...  But keeping the high
> quality oscillator running continuously should solve that....
> 

Some colleagues of mine at JPL and I talked about this some years ago, 
and a similar concept for a PSK31 rig to do the same sorts of things.

One challenge is the frequency stability needed. Practical experience 
says that if you're trying to do automated HF packet, you need perhaps 
10Hz frequency accuracy (i.e. 1 ppm at 10MHz).  That's the total 
differential, spread between Tx and Rx end.  It is tough to get 1ppm 
from an inexpensive low power crystal oscillator (the usual TXCO gets 
close, but only after some thermal equilibration after power is 
applied).  Now, if someone were to write a decent receive end software 
decoder that could tolerate wide frequency ranges, that would help a 
lot, but the usual scheme is pretty narrow band, and relies on a human 
operator to click on or tune to the signal.

There are, also, a lot of inexpensive TCXOs now available from Vectron, 
etc, that don't consume much power. +/- 0.5 ppm is about the limit of 
performance.



> But the market for HF APRS is so small.... Now that the APRS-IS
> is so pervasive...
> 
> Bob, Wb4APR