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Re: New baseline for GEO



Given the links below, then here is my "present" design concept for
SuperGeo:

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

MISSION: is to provide one AX.25 packet, one voice, and one PSK-31
         multiuser comm channel for special HAM radio applications.
         Packet is available always, but voice and PSK-31 will be
         always under the control of a scheduled Net Control for
         the given event.  Duty cycle will be low.

ACCESS:  The transmit duty cycles are low.  The Voice/PSK-31 channels
         will only be activated to support special events on schedule.
         Schedule will be available live on the 1 minute packet beacon.

GROUND STATIONS:
   USER: We want a user with an ARROW antenna and FM rig to be able
   to receive and use ALL signals.  He may need higher power or
   better antenna for uplink.

   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.

TRANSPONDER DESIGNS:

   PACKET:  Dual redundant 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.  Using 40W RF power AMP (but at low 10% dutycycle)
   gains  another 3 dB.  Downlink is on 145.825.  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. (70% of time?)
   Higher power base stations can do better.  Downlink is on 2m.  Uplink
   is on 70cm.

   PSK-31:  Downlink is the same 2m FM audio channel.  Uplink is 25W SSB
   transceivers running PSK-31 or other narrowband modes in 3 KHz wide
   spacecraft receiver.

This is not the ideal spacecraft for anyone, but it is what we could do
off the shelf if given the opportunity...

DOWNLINKS to an ARROW ant   2m AX.25  2m FM & psk
--------------------------  --------  -----------
TX power        40 and 20W   46 dBm    43 dBm
TX Antenna Gain               0 dBi     0 dBi
Polarization loss            -0 dB     -3 dB
Resulting EIRP               46 dBm    40 dBm

Path Loss                  -167 dB   -167 dBm
Receiver Antenna Gain        10 dBi    10 dBi
Received signal            -111 dBm  -117 dBm
Required for 12db SINAD              -121 dBm
Typical TNC needs          -117 dBm
Sky noise                     3 dB      3 dB
-------------------------  --------  --------
Margin                        3 dB      1 dB

Notes:
 - The uplinks from a 50W mobile rig will be 4 dB better
 - The downlink can only be on a small percentage of time
   because a 20W RF amp will likely draw 60W of DC power
   and only about 10W average will be available...

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

de WB4APR@amsat.org, Bob




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