[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Fade remover



You know, the sad thing about this is that is the extra margin
gained by FEC would have effectively been free.. no cost...

I think they were afraid that the PSK400 modems would be obsolete,
but that hardly matters now that soundcard modems are out, does it?

Am I correct in assuming that most of the Reed-Solomon and Vitribi encoding 
could be done with lookup tables if necessary?  I thought
that was the case.  If so, the "SLOW" COSMAC 1802 theory goes right out the 
window...

Maybe next time...

Fred W0FMS


>From: Phil Karn <karn@ka9q.net>
>Reply-To: karn@ka9q.net
>To: rwmcgwier@home.com
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Fade remover
>Date: Tue, 6 Feb 2001 17:04:32 -0800
>
> >Since the command stations will never do any
> >of this, we are all wasting amsat-bb bandwidth.
>
>This strikes a real nerve with me, and I can't resist the need to vent
>any longer.
>
>Years ago, I started lobbying the P3D powers-that-be to use more
>efficient downlink modulation and coding.  Although the P3D IHU is
>nearly identical to the mid-1970s design that flew on Phase 3A, nearly
>all of the complexity associated with FEC is on the receiving
>end. Thanks to a few minor advances in personal computing technology
>over the past quarter century, we can now easily handle those
>complexities. That gave us the opportunity to vastly improve
>spacecraft downlink performance, especially under fading conditions,
>with only a software change to the spacecraft.
>
>I was told not to fix things that aren't broken. I responded that few
>amateur spacecraft went into operation without a hitch, and that
>amateur satellite downlink budgets are often overly optimistic. For
>example, after the AO-10 launch many stations had difficulty receiving
>error-free telemetry because of the spacecraft's damaged 2m antenna,
>abnormal attitude and spin.  Having the extra downlink margin for a
>spacecraft as complex as P3D might be good insurance. And I was
>willing to write the necessary ground software. I'd already done the
>hard parts, including several Viterbi and Reed-Solomon decoders.
>
>I got nowhere. One insider responded, "You know perfectly well why the
>Phase 3 links are the way they are. That's my last comment on the
>subject."
>
>To say that such an insular attitude can only demoralize volunteers
>and discourage contributions to a project that relies on them is an
>understatement, at best. There was a time when I'd take this as a
>challenge, to see just what I could do within the constraints of the
>existing design.
>
>But now I think, "Why bother?" After all, it's now almost 3 months
>after the launch and the team has yet to publicly disclose all the
>material information they have about the propulsion system
>problems. They obviously don't want our help, so why should we force
>it on them?
>
>Phil
>
>
>
>
>
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org


AMSAT Top AMSAT Home