                        AN AMSAT MOBILE TRAKNET

    Commercially, there are two distinct advantages of the global nature
of satellites which cannot be easily met with terrestrial systems:  wide-
bandwidth point-to-point and mobile applications.  With the availability 
of telephone, cable, and the internet to link HAMS at fixed sites to each 
other routinely, we are wasting a lot of potential of our very valuable 
AMSAT resources by ignoring mobile applications.

     HAM radio is on the move.  Any survey will likely show that many
hams only have time to play radio while mobile, and similarly, whenever
a ham contemplates a long trip, his HAM radio is high on the packing 
list.  Although many dream of taking along an HF mobile to play with 
and to report their progress back home, the $1000 to $2000 investment  
is just too much of a risk.   Two meters is fun, and can bring emergency
aid, but it just doesn't provide the nationwide coverage that is needed
for the mobile HAM traveler far from home, the offshore boater, or 
first-response teams arriving in a disaster area.  In many cases, just 
a brief position/status report is all that is needed to assure the health 
and welfare of the traveler or to summon assistance or alert other comms
channels.

        What we need is a new perspective which takes advantage of some 
very unique capabilities to exploit a small portion of our AMSAT on-orbit 
capacity to the mobile requirement.  Fortunately, there are several 
AMSAT's that are VERY EASY to transmit to from the mobile using only a 
2 meter 25 watt FM mobile radio.  The ubiquitous radio that EVERYONE has...

UPLINKS:   Lets look at the 1200 baud PACSAT uplinks.  These uplinks are 
unique for several resons that make them ideal for the mobile environment 
as follows:

  1)  The 2m uplink from a mobile omni antenna has a 9 dB advantage over 
        a similar 435MHz link due to the 3 times larger antenna aperture
  2)  There is no tuning or tracking required on the uplink since the 
        doppler on 2m is less than 3 KHz.
  3)  Any 25 watt mobile 2m FM rig can be used as the transmitter
  4)  Any TAPR-2 compatible TNC can be modified for the uplink for $2
  5)  World Wide Coverage
  6)  NO software or hardware on-orbit modifications to the satellite.

Reportedly stations running as low as 7 watts into an indoor omni antenna
have reported success with the 1200 baud PACSATS.  This means that even 
back-packers with an HT and handheld gain antenna could get emergency or 
priority traffic into a Pacsat...  from anywhere on earth!  Figure 1
shows the results of the SPRE experiment during STS-72 when there was
a digipeater on the Shuttle for station position/status reporting.

DOWNLINK:  OK, so the 2m UPLINK is easy and anyone can do it, so what 
about the downlink?  This is not so easy.  The path loss omni-to-omni 
is 9 dB worse, the satellite is only transmitting a watt or so for 
another 13 dB worse performance, plus it REQUIRES doppler tuning, a $250 
PACSAT modem and a $1000 all mode UHF receiver!  In most cases, all 
successful Pacsat stations use high gain antennas and automatic tracking 
to make up for the more than 22 dB performance diffeence on the downllink.  
This is not something that most operators will want to add to their mobile.  
But what if the mobile application did not need to receive data, but
only send it?

TRAKNET:  The combination of EASY uplinks, MINIMUM downlinks, and an
application that often only needs a one way exchange of data, such as the
mobile position/status report is the whole idea behind TRAKNET.  Only a 
few automated downlinks are needed every 1000 miles or so to receive the 
mobile data and to provide it into a nationwide system of linked ground 
stations.  These ground stations relay the mobile position/status reports 
onto local mobile vehicle tracking channels and onto the internet.  Anyone 
may access the data live on VHF, HF or via the internet.  TRAKNET is not
just a future idea, it can be implemented immediately with existing
equipment and satellites.  Yes, even the INTERNET ground stations exist:

     ATLANTA:  http://www.wadsy.radio.org/aprs/index.html
     CALIF:    http://sboyle.slip.netcom.com/LIDSAPRS.html
     CHICAGO:  http://tbcnet.com/~jleonard/noiltest.html
     MIAMI:    http://www.bridge.net/~sdimse/javAPRS.html
     ONTARIO:  http://www.peel.com/javAPRS.Html
     WASH-DC:  http://web.usna.navy.mil/~bruninga/aprs.html

But the problem is that none of these sites is yet listening to the 
PACSATS mostly because setting up an automatic PACSAT ground station is 
not trivial and the guys who play with the WEB all day are not the same
guys that are necessarily fully invested in PACSAT hardware...  All we
need are probably 8 stations scattered over the continental USA to 
implement a reasonable TRAKNET system.

MOBILE STATION:  A mobile station consists of nothing more than a typical 
2 meter FM radio and a modified TAPR-2 compatible TNC as shown in figure
3.  Optional accessories are a GPS for moving position reports, and a 
laptop for entering messages.  Most modern TNC's will accept the GPS data 
directly and will transmit the data in a timed packet burst.  There is
even a tiny handheld TNC's called the APRS Mic-Encoder that includes 
front panel switches for selecting 1 of 7 pre-canned status messages 
without needing a laptop to change the status report.  The modifications 
to the TAPR-2 TNC are to simply EXclusive OR the transmit data with its 
1200 Hz clock and to filter the result to the Mic input of the radio.  
The following circuit will do this with nothing but an 89 cent standard 
7400 quad 2 input NAND gate connected as an XOR gate to the two points 
shown.

  19-20 J5            |\     
  TXD ---*------------| |0--*
         |         *--|/    |   
         *---|\    |        *---|\      
             | |0--|        *---| |0--*--/\/\/\--*-------*       
         *---|/    |  |\    |   |/               |       \ 1k
         |         *--| |0--*                   ===.2uF  / <----*> To Mic
  TXC ---*------------|/                         |       \
  U10A pin 6                                     |       /
                                               -----   -----
                                               /////   /////

The pin numbers shown are for a PacComm TINY-2.  

TRAKNET PROTOCOL:  The problem with any AMSAT is the very low bandwidth 
available compared to the very large worldwide amateur population.  At
first glance, the prospect of increasing the number of users on a Pacsat
channel by a hundred fold raises lots of red flags in the minds of those
stations who already find the 10 minutes of a satellite pass to be too
short for any meaningful dialoge.  But what if each of these hundreds of
of new users was limited to only a few seconds per orbit?  Then as many
as 200 stations per footprint could be tracked.  That is the only objective
of the TRAKNET protocol, to allow everyone to transmit a few single 1 
second position/status reports during the closest point of approach over 
their location.  If only one channel is designated for TRAKNET, then the 
other 3 channels are free to normal PACSAT use and no ammount of congestion 
on the TrakNet channel can interfere with existing users on the other three.

TRAKNET SATELLITES:  There are currently five 1200 baud Pacsats on orbit.
One, WO-18 has actively invited UI frame digipeating and leaves DIGIPEAT
on most of the time.  The problem is that the WO-18 downlink is difficult 
to receive un-attended due to a spur tone in the middle of the data which 
makes receiver lock a difficult and manual process.  AO-16 has had its 
digi ON for the last 6 months.  Other PacSats occasionally have DIGIPEAT 
turned on, but there is no formal policy.  The purpose of this article is 
to encourage the designation of one good channel as a gathering point for 
TRAKNET experiments, and then progress can be made and the potential of 
TRAKNET can be evaluated.  Here are the frequency plans of the existing 
PACSATS:

DIGIPEATER FM Manchester UPLINKS CHANNELS         DOWNLINK
---------- -------------------------------------- ---------
AO-16                 .860      .900 .920 .940    437.051
LU-19            .840 .860 .880 .900              437.153
WO-18                           .900              437.104
ITMSAT-1                  .875  .900  .925  .950  435.822

ADVANCED MOBILES:  While the preceeding was written to emphasize the
ease of using the PACSATS by anyone for emergency or priority status/
position reporting, there is certainly no reason why a full two way
PACSAT communications system cannot be added to most mobiles.  Omni
PACSAT downlinks are possible and the addition of only a modest gain
antenna will certainly help.  Advantages are the small size of a 6 dB
two element UHF antenna and the SHORT cable run found in a mobile.
Rather than a $1000 SSB rig, a $90 QRP HF rig and a UHF downconverter
could do just as well.

CONCLUSION:  The advent of the handheld GPS unit for under $199 has 
brought thousands of mobile amateur radio operators into the world of 
mobile data.   Similarly, the state-of-the-art in automatic PACSAT 
ground station has been improving with many recent software packages 
to make un-attended automatic ground station quite easy.  The problem 
is that these two communities of expertise have so far had little cross-
interests.  It seems that the time is now to merge these technologies 
into a new amateur application that takes advantage of the unique 
capabilities of each and fuels the develpoment of an Amateur Radio 
Mobile Satellite System.  
