[amsat-bb] Re: Eagle U/V modes
kb5mu at amsat.org
Wed Oct 11 00:33:07 PDT 2006
At 9:08 PM -0700 10/10/06, Greg D. wrote:
>1. I was also excited by what I heard about the Text Messaging
>proposal. Has anybody approached (or future tense, could anyone
>approach) Kenwood for a re-program of their TH-D7?
It will take a lot more than reprogramming. The Kenwood radios
contain the wrong kind of modem, and it's implemented in hardware
(the same on both the HT and the mobile). It will take a rather
complete redesign of the unit to work on Eagle's text messaging mode.
In any case, it would be premature to approach manufacturers. The
parameters aren't fixed yet, and need to be subjected to peer review,
implementation, and testing before they can be.
I would not expect big commercial manufacturers like Kenwood to be
involved in the first round of hardware, any more than they were
involved in making packet TNC's before TAPR productized and
popularized them. And a fully-integrated radio/TNC like the TH-D7 and
TM-D700 was still longer in coming. So, don't hold your breath.
>2. What I thought I heard at the Symposium was that we wouldn't
>need such a massive station to work Eagle's traditional UV
The U/V transponder isn't all that different from the ones we've
flown before on high orbits. The size of the spacecraft constrains
the antenna designs that are possible at VHF and UHF. The antenna
systems haven't really been designed yet for the new spaceframe, but
the example drawing showed three dipoles on VHF and a few patches for
UHF. Those are not killer antennas, and there are no magical
modulation or coding tricks available for SSB and CW users.
It might be possible to allocate more power to the downlink than
before. Or maybe not; we do want to run the analog and digital
payloads simultaneously (all the time) and the power budget hasn't
been finalized. I believe the current plan is to run more power than
before, but not spectacularly so.
This not being Star Trek, we can't improve the uplink by shunting
warp power to the receivers. The SDX implementation technology will
help on the uplink by solving the alligator problem once and for all,
but it will still be necessary to use enough power+gain on the ground
to close the link to the distant spacecraft with its compromise
I'll leave the forecasting of exact ground station requirements to
those who have studied the link budgets. And then I will take the
results with a grain of salt. I hope it will be better than before.
But what's really better than before is the ACP (Advanced
Communication Package, that is, the digital stuff), and people who
don't want to put up large antennas should really be looking forward
to that rather than the U/V transponder.
In my opinion.
kb5mu at amsat.org
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