[amsat-bb] Re: Eagle U/V modes

[Paul Williamson]

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 
>transponder.

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 
antennas.

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.

73  -Paul
kb5mu at amsat.org