telecom (05/17/82)
>From JSOL@USC-ECLB Mon May 17 13:50:54 1982
TELECOM AM Digest Tuesday, 18 May 1982 Volume 2 : Issue 62
Today's Topics:
ACTS and ABC - Automated Coin Collection
Bell 212 Frequency Selection
Satellite Propagation
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Date: 4 May 1982 1651-PDT
From: Ian H. Merritt <MERRITT at USC-ISIB>
Subject: ACTS and ABC - Automated Coin Collection
I receved the following documment from a friend who was then a TSPS
operator, one year ago -- just before LA cut over to the ACTS/SSAS
system. In light of some recent discussion over automated coin
telephone service, and automatic calling card service as well, I am
submitting it to the list.
[This article is 19,000 characters long, and thus is too long to mail
out via the digest. It has therefore been made available for FTP
distribution. Thanks go to Ian Merritt, Richard Lamson, Don Woods,
Jim Mcgrath, Roger Duffey, and Will Martin for providing space on
their machines. If you find yourself unable to FTP the file, you
should send mail to TELECOM-REQUEST@USC-ECLB and I will mail you a
copy.
[USC-ISIB] PS:<MERRITT.TELECOM>ACTS.DOC
[MIT-MULTICS] >udd>sm>rsl>telecom>acts.text
[PARC-MAXC] [maxc]<Woods>Telecom.ACTS
[iris]<Woods>Telecom>ACTS
[note that the "." vs ">" is correct as shown for the two file names.]
[SU-AI] ACTS.TXT[T,JPM]
[OFFICE-8] <WMARTIN>ACTS.TELECOM
[MIT-AI] DUFFEY;TELCOM ACTS
[Note: you can TYPE or FTP the file from SU-AI without an account
or password.]
For the benefit of those people who read this on USENET as
fa.telecom, I will follow this digest with a copy of the ACTS text in
full.]
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Date: 15 May 1982 12:25-EDT
From: Peter J. Castagna <PC at MIT-MC>
Subject: Bell 212
To: lauren at UCLA-SECURITY
The frequencies selected in the 212 were selected merely because they
were very simple to generate from a standard (3.684Mhz) crystal
and were multiples (easy to switch by selecting one or another
output of a divide-down-by-two counter array). Vadic's frequencies
were selected for INTELLIGENT reasons.
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Date: 15 May 82 22:48:31-EDT (Sat)
From: J C Pistritto <jcp@BRL>
Subject: Satellite propagation
It is quite possible, even likely, that a satellite in say a 2
to 3 hundred mile orbit could be hit FULL QUIETING (50db SINAD), by a
handheld walkie talkie, much less a 20watt mobile unit. When
travelling in the midwest recently, I was able to consistently hit
repeaters at 100 miles with only 5 watts of power, and was informed I
had a full quieting signal on several of them. With 45 watts, I was
able to hit almost everything I could reach at all, full quieting.
The only major obstacles I encountered were, the curvature of the
earth, cities, and other stations on the same channel. None of these
are a problem in space. The home TV type receivers produce a signal
with over 45db S/N, (to obtain a clear picture), and typically those
have roughly 30db antennas, and are receiving 5 watt or so satellite
transmitters, (power is EXPENSIVE up there). That's on a signal at a
much higher wavelength too, where circuitry is almost 'magic',
(particularly the front end preamp). At lower frequencies, (70 cm
would be my personal choice, ~ 440 Mhz), and a lower noise
requirement, (30db would do fine, 20db in a pinch), it is ENTIRELY
possible that the problem could be overcome with a good ground plane
antenna properly oriented.
Even *older* satellites contain receivers better than anything
a ham is likely to own, also, as the cost of orbiting a satellite,
(particularly a geo-synch one), vastly overshadows the cost of the
reciever. Sounds definitely plausible to me.
-Joe Pistritto-
N3CKF
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End of TELECOM Digest
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