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Re: New baseline for GEO (rev-1)



SuperGeo (rev-1)

Sorry to bother everyone with my rambling thoughts, but here is the latest
revision of what my goals would be for an off-the shelf GEO opportunity
based on amsat-bb feedback.  It needs some  help on the linear part...

New KEY elements:
 1) Full time Mode-B U/V linear transponder for SSB cw and PSK31 though it
    Goal is to work it with a portable arrow even it means many
    restrictions.

 2) Part time 50W single channel FM donwlink for special events hearable
    on any mobile but operated usually as a directed net.

 3) APRS Packet bulletins once every 5 minutes on 144.39 posting the
    schedule of events to all mobiles on the continent (and the European
    APRS frequency when it drifts over Europe)

 4) Occassional AX.25 digipeating for special events and wilderness
    travelers with downlink on 145.825 receivable by mobiles.

The purpose of #3 is for the thousands of APRS mobiles, once every 5
minutes they will receive a packet shwoing them ON THE FRONTPANEL of their
radio, the next scheduled event on the FM transponder.  THink of this as a
"tiny web-page" of real-time info on what the HAM community is doing with
this asset.  Due to congestion on the main APRS frequency, you will not
get all of these.  But you only need one to be updated.  It will go to
your DX list so it doesnt detract from your other messages, and also so
that any Kenwood 2000 rig will also display it on its front panel too.
Just anytime you are in your car, just push the DX button and your radio
will show you what is coming up next and when!

Now, can someone nail down the limtations we will have to make to make a
Linear Transponder that can only have 10 Watts of AVERAGE DC power and yet
can be comfortably worked with a portable ARROW set up.  Even if it has to
be a single channel, just tell me what it takes.  I dont have time to do
this detail, with the other 2 satellites I am on deadlines for.  But now I
think I know what we can do for transponders.  Here is a review of the
situation:

ORBIT:     Drifting GEO (slightly supersync)
ATTITUDE:  None (tumbling, rates unknown)

MISSION: is to provide one full time (thou minimal) linear mode B
         transponder, and part-time, one AX.25 packet, and one FM voice,
         comm channel for special HAM radio applications.
         Packet is for direct-to-user-front panel real-time bulletins
         about scheduled operations and occasional special events.
         The FM voice (and, if necessary the linear transponder) will
         always be under the control of a scheduled Net Control for
         the given event.  Duty cycle will be low.

ACCESS:  THe linear transponder is on full time (we hope).  The transmit
         duty cycles for the FM modes are low.  The FM Voice
         will only be activated to support special events on schedule.
         Schedule will be available live on the 5 minute packet beacon.

GROUND STATIONS:
   USER: We want a user with an ARROW antenna and SSB rig to be able
   to hear at least one channel on the Linear downlink and anyone with
   an FM rig and an arrow to work the FM transponder when activated.

   NET CONTROL:  Must also be operable portable for special events.

   MOBILE:  A mobile with a center-roof 57" roof mounted whip (3/4 wave)
   can receive the packet bulletins direct at middle latitudes on the
   existing APRS channels.  And holefully hear the FM downlink when used
   (on a different freq).

TRANSPONDER DESIGNS:

   PACKET:  Dual redundant 50W Packet Transponders for TT&C, Bulletins,
   and special users (those with the need)... Two separate digipeaters
   Operating independently on their own orthogonal monopoles gives 3 dB
   link advantage.    Downlinks are on 145.825 and the continental
   APRS freq.  Uplink is on 70cm and will take lots of gain and power.

   FM VOICE:  2m Downlink is just at 12 dB SINAD for .18 microvolt
   receiver using a 3 element Arrow style antenna.  User should have 6
   elements for better copy...  Uplink takes 50W to the Arrow, but you
   only make it in when satellite tumble favors you. (50% of time?)
   Higher power base stations can do better.  Downlink is on 2m.  Uplink
   is on 70cm. (must use external diplexer on ARROW!)

   Linear transponder is limited to whatever it takes to be able to
   leave it on all the time and work it on an ARROW.

This is not the ideal spacecraft, but it is what we could do
off the shelf if given the opportunity... Here are the link budgets I
came up with for the FM parts.  Someone else can detail the linear part.

DOWNLINKS to an ARROW ant   2m AX.25 and FM voice
--------------------------  ---------------------
TX power        50 Watts     47 dBm
TX Antenna Gain               0 dBi
Polarization loss            -3 dB
Resulting EIRP               44 dBm

Path Loss                  -167 dB
Receiver Antenna Gain        10 dBi (arrow) 5 or 7 dBi for mobile
Received signal            -113 dBm
Required for 12db SINAD:             -121 dBm
Good TNC needs:            -119 dBm
Sky noise                     3 dB      3 dB
-------------------------  --------  --------
Margin                        3 dB      5 dB (3 or 5 dB worse for mobile)


Again, for the SPECIAL usages there will be two uplinks, one for net
control (priority) and one for the net...

Correct me please if I have it wrong, and someone please review everything
posted so far and give a good LINEAR link budget including whatever
constraints are required to make it work for the Arrow portable.

Thanks
de WB4APR@amsat.org, Bob


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