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From: karn@petrus.UUCP
Newsgroups: net.ham-radio
Subject: Re: Quality of NASA space-to-ground links
Message-ID: <356@petrus.UUCP>
Date: Fri, 24-May-85 22:32:00 EDT
Article-I.D.: petrus.356
Posted: Fri May 24 22:32:00 1985
Date-Received: Sat, 25-May-85 09:40:45 EDT
References: <10912@brl-tgr.ARPA>
Organization: Bell Communications Research, Inc
Lines: 43

Regarding my own question, I recently had the chance to put it to an
astronaut (Ron Parise, WA4SIR). He said he had wondered the same thing, and
didn't really know the reason for certain. We came to a consensus on
a couple of possibilities, which I paraphrase here:

1. Pickup from noise sources on board (Owen Garriott might have just found a
quiet spot when he operated 2mFM). The orbiter is filled with blowers, fans,
and is quite noisy. These might have been amplified by compressors in the
regular speech processors (see #4).

2. The air-to-ground links are digital only to the TDRS ground station.
From there they are relayed in analog form over a concatenation of satellite
and landline links which can each add their share of noise.

3. Noise in the wireless headset links used on board.

4. Large amounts of compression and/or clipping in the speech processors,
combined with incorrect gain settings and astronauts talking away from
their microphones.

Regarding the sub-topic of monitoring the HF bands from orbit, I suspect
that conditions on the lower frequencies would be rather poor. We hams have
already had experiences with sending signals through the ionosphere with the
Oscar and RS Mode A downlinks on 10m, and the HF beacons experiment on
UoSAT-Oscar-9. In each case, if the band in question is "open", you'll have
a hard time penetrating the ionosphere for earth/satellite communications.
Even when a low frequency band, e.g., 80m, is closed, it's because of high
ionospheric absorption so again you're going to have a rough time.

For example, whenever 10 meters is open, Mode A reception when the satellite
is just above the horizon is very poor and in fact you're just as likely to
hear the satellite when it's below the horizon.

DXing the VHF/UHF bands and above is likely to be more productive, since you
can see everything in line of sight and the ionosphere rarely interferes.  I
remember a story a while ago (I forget where) which listed a few UHF TV
stations which were receivable on the moon. The criteria wasn't signal
strength, it was lack of other interfering assignments to the same channel.
I remembered this story because one of the stations cited was WMPB-TV on
channel 67 in Owings Mills, MD, where I used to spend college summers
working as a broadcast technician.

Phil