In the time since the San Diego meeting, I have come to realize that:
1 - Nothing is ever final.
2 - The decision about bands for the DCP (digital communications
payload) is likely to be made in some combination of the following
venues, in none of which you are likely to find me:
A - AMSAT-BB
B - AMSAT Board Meetings
C - Meetings with shadowy DoD figures without names
D - IARU, ITU, ARRL, QCWA, or Wuoff-Hong Society meetings
3 - Many of the decision makers (especially those speaking the loudest)
think that SSB is the way of the future and Shannon's Law means that sex
offenders have to register with the police.
4 - It really doesn't matter to me which bands are chosen, as long as
they meet certain basic criteria.
In that spirit, I decided to distill the major technical constraints
which we agreed on at the San Diego meeting, in order to give a basic
set of rules which would provide us a workable bandplan for this
satellite. The only legal/regulatory constraint I applied to this list
is that we are unlikely to GAIN privileges. Someone else can decide how
likely we are to lose them.
The constraints, and their reasons, as I see the consensus from the SD
meeting:
1 - The uplink band must be chosen from the set of { L, S1, S2, C }.
The lower bands simply don't have the bandwidth necessary for what
we want to do, and would have unwieldy antennas.
The higher bands are much more difficult due to the pointing
accuracy required for antennas and the difficulty of generating
significant power and low noise figures.
2 - The downlink band must be chose from the set of { S1, S2, C }.
The same reasons as constraint #1, with the added constraint that
L-band is not legal for downlink (which falls under the "we're not
likely to GAIN privileges" category).
3 - The uplink and downlink bands must be distinct. This means no C-C
or S1-S1.
The bands are simply too narrow to allow for practical duplexers in
the quantity we are talking about (~36).
4 - The uplink band must not be used by any other payload on Eagle as a
downlink.
Obvious interference issues.
5 - The downlink band should not be used by any other payload as an uplink.
Obvious interference issues.
6 - Sharing of uplink bands or downlink bands MAY be possible, but
probably isn't necessary.
Taking constraints 1-6 together, the choices are (in the form A/B where
A is up, B is down):
{ L/S1, L/S2, L/C, S1/S2, S1/C, S2/S1, S2/C, C/S1, C/S2 }
In addition to the above "hard facts", we can add in the following
concerns which were expressed at the meeting:
7 - We would prefer not to use S1 as a downlink because of possible
interference from WiFi devices.
8 - Fear of L being taken away
9 - Uncertain legality of S2 in ITU Region 1
This leads to the following matrix, which I believe effectively boils
down the decision process from the SD meeting:
Bandplan 7 8 9
L/S1 X X
L/S2 X X
L/C X
S1/S2 X
S1/C
S2/S1 X X
S2/C X
C/S1 X
C/S2 X
The only bandplan with no X's is S1/C, which is what we chose at the
meeting. Obviously, there are now additional concerns which have been
raised:
- S1-Uplink being taken away
- #8 not being as big a deal as we thought.
This would change the matrix.
I welcome your thoughts, especially if you feel I have misrepresented
the SD meeting consensus.
Thanks,
Matt, N2MJI
