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AO-27 Internet Monitor Gateways



AO-27 is one of the most popular AMSAT's because it allows Handheld
VOICE communications.  As part of my focus on using Satellites for
mobile/portable Amateur Radio operations, this paper suggests ways to
improve the visibility of such operations by tying the AO-27 downlink 
into the internet and WEB pages so that everyone can monitor the 
activity.  This is very useful for outreach to kids and schools.
 
All we need are a few stations monitoring the downlink and feeding it
into the internet for access.  These ground stations need only a UHF 
receiver and fixed antenna.  Only 9 or so would provide 90% coverage
for all passes over the USA.  THere are two types of information on 
the downlink, voice and PTT tone bursts.  The PTT tones here are only 
the 0.2 second ID burst that can be appended to the end of any voice 
QSO by the new Kenwood THD7 dual band 5W HT or from any radio using 
the APRS Mic-Encoder.  First I will address this tone burst since it 
is the easiest.
 
The 0.2 second tone bursts contain the stations' position, course, 
speed and brief Status.  NOTE! we are NOT suggesting packet operations 
on AO-27, but these computer-readable bursts are invaluable in the 
rapid and precise identification of users.  On the ground, these bursts 
can be distirbuted worldwide almost instantly by the existing APRServe 
internet infrastructure and instantly plotted on many LIVE WEB pages  
such as http://www.aprs.net .  Thus, not only do we have a self logging
satellite voice communications system, but also the ability to receive
emergency text communications from anyone with an HT in the wilderness
via AO-27 (and any other FM voice or AX.25 satellite)
 
Since there will be multiple receiver sites all feeding their data 
into the same worldwide distribution system, they can use fixed
antennas and fixed doppler and only concentrate on their optimum area of
the sky because:
 
  1) AO-27 is only on during the day, during North to South passes
  2) During the first third of the pass, the doppler is about +7 KHz
  3) During the first third of the pass, the satellite is NORTH
 
Thus, a fixed tuned receiver at 435.807 MHz (+7Khz) using only a 3 
element UHF beam or Corner reflector pointed north will capture almost
HALF of the available passes.  Higher gain is NOT desired since it would
not see passes to the northeast and northwest.  Remember, your station is 
only a small piece of a nationwide distributed listening network.  The
geometry of the sky from your location where the doppler is between +6 and
+8 KHz extends from your northern horizon to almost 45 degrees.  The
sector is a full 90 degrees wide from your NE to your NW.   No more than 3
elements should be used or the azimuth coverage would not be sufficient.
If you want to pick up an added 3 dB, then use a pair of stacked 3 element
vertical beams to narrow the vertical pattern while preserving the
horizontal width.   Other creative antennas aproaching 10 dB can be
designed for just this sector.
 
OPERATIONS:  Any such UHF receiver configured as noted above, will
receive the downlink during all daytime passes.  To link those
brief 0.2 second tone bursts from the THD7 users into the worldide
APRS internet system, all you must do is have a TNC with the MYALIAS
of RELAY listening on UHF and transmitting on 2 meters on 144.39.
 
VOICE INTERNET ACCESS:  This is not my area of expertise, but I assume 
that using "REAL-AUDIO" techniques, that creative WEB masters can
create WEB pages to capture and make available the brief 5 miunute
pass audio from these receiver to anyone in real time.
 
PLANS:  I will begin work on such an AO-27 Monitoring receiver for
Maryland.  Just looking at a USA map, if we had similar sites in
Atlanta, Chicago, Miami, Houston, Kansas CIty, Denver, LA and SFO,
then we would have quite a network, capable of capturing most passes.
Already you can monitor such live HT users via MIR on our automatic
MIR monitoring WEB page http://web.usna.navy.mil/~bruninga/mirex.html
This is a similar system to monitor the AO-27 downlink.
 
THD7 USERS:  To enable the short tone burst at the end of your PTT
voice operations, set TRANSMIT to PTT, rate to 30 secs, PATH to RELAY.
Keep your STATUS text short or your data burst will be longer.
You can dial in any one of the 7 pre programmed COMMENTS, but please 
avoid EMERGENCY unless its true.  Uplink is on 145.85.  The internal
TNC cannot operate cross band, so you will NOT be able to decode
any other stations you may hear on 435.800 + doppler.  But everyone
else monitoring can.
 
If you do not have a THD7, you can add a Mic-Encoder to any HT
using either the original TAPR Mic-ENcoder or the new Mic-Lite.
See http://www.toad.net/~clement/mim2.htm
 
de WB4APR, Bob

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