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

[Greg D.]

Hi Paul,

Thanks for your thoughts.  I kind of figured the Kenwood would be out, but 
it was worth asking.

As for the link budget on UV, I think the uplink side isn't the problem - a 
bigger amp can offset a smaller antenna, within reason.  But the downlink is 
my worry; I may only have half the antenna that would otherwise be expected. 
  Sounds like we just don't know yet, so I'll keep monitoring the progress.  
No panic.

Thanks again,

Greg  KO6TH


----Original Message Follows----
From: Paul Williamson <kb5mu at amsat.org>
To: "Greg D." <ko6th_greg at hotmail.com>
CC: amsat-bb at amsat.org
Subject: RE: [amsat-bb] Re: Eagle U/V modes
Date: Wed, 11 Oct 2006 00:33:07 -0700

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