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From: karn@petrus.UUCP
Newsgroups: net.ham-radio,net.space
Subject: Quality of NASA space-to-ground links
Message-ID: <353@petrus.UUCP>
Date: Thu, 16-May-85 23:54:26 EDT
Article-I.D.: petrus.353
Posted: Thu May 16 23:54:26 1985
Date-Received: Sat, 18-May-85 00:35:38 EDT
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Organization: Bell Communications Research, Inc
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Xref: watmath net.ham-radio:2713 net.space:3989

This is a question that's bugged me for some time.

Those of us who are space junkies have gotten used to listening to
space-to-ground audio links that are, shall we say, somewhat less than
"telephone quality". While the overall intelligibility has gotten better
over the years, it is still worse than I would expect.

In the case of the space shuttle, which uses digital transmission (delta
mod) for its primary (non-UHF) audio links, I had assumed that the noise you
hear when an astronaut opens his mike must be due to things like ventilating
fans on board (after all, air doesn't move by convection without gravity).

However, when Owen Garriott made his famous DX-pedition, using the same
headset connected to a 2m FM handie-talkie, his audio quality was absolutely
clear -- virtually no transmitted noise or distortion. If I hadn't already
been familiar with his voice from things like interviews and press
conferences, I would have suspected a hoax. So where does all the noise come
from in the NASA chain? Do the orbiter avionics use large amounts of speech
compression or clipping, or what? Should we hams offer to replace all of
their communications gear?

Phil