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Re: New baseline for GEO (+SSB)

New Idea for Super Geo!

WAS: If we put all the spacecraft power (say 100W) into an FM donwlink
then every mobile in the hemisphere could tune it in.  Total operating
time would be about 2 or 3 hours of scheduled directed nets a day.

NEW: If we put all the power into a SINGLE SSB downlink (FM uplink) then
we can use it maybe 24 hours a day!  BUT it eliminates 99.5% of all
mobiles being able to hear it (unless they carry an SSB)..

This gains all the LINK and average POWER advantages of SSB, and elimnates
all the disadvantages of a wideband transponder (linearity, AGC pumping,
sharing, etc).  But the BIG downside is that it eliminates the primary
advantage of a single HAM channel from space, and that is it's ubiquity
of being able to be received by everyone.

But, if someone would build us a 10W PEP single channel SSB transmitter
we could fly it too and leave it on all the time.  Then only turn on the
FM transmitter for special events intended for all of HAMdom...

Maybe we dont need 10W?  I dont have time now to re-do the link budget for
2m downlink to ground user with an ARROW antenna and 20 dB SNR (I want
CLEAR easy-listening reception)...

Or we make it a full linear SSB transponder (but only 3 KHz wide) so that
we dont have to deal with wideband issues and power sharing, but get the
single channel link advantages...  We have to get the average DC power
below 10W to leave it on all the time (and someone else has to be fully
responsbile for building it)...


The SuperGeo idea was:  http://www.ew.usna.edu/~bruninga/supergeo.html

On Thu, 31 Jul 2003, Bob Bruninga wrote:

> 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.
>    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.
>    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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de WB4APR@amsat.org, Bob

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