[fa.telecom] TELECOM Digest V2 #61

telecom (05/14/82)

>From JSOL@USC-ECLB Fri May 14 16:33:21 1982
TELECOM AM Digest      Saturday, 15 May 1982      Volume 2 : Issue 61

Today's Topics:	     Product Report - VADIC 3451
                      INWATS Prefix Assignments
              Query - When Did N1X And N0X Start In LA?
                      Mobile Radio Through ATS-3
     Area Code & Prefix Assignment Listing - V&H Coordinate Tape
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Date: 13 May 1982 18:23:57-PDT
From: decvax!minow at Berkeley
Re: Vadic 3451

I have one and it seems fine.  If you're going to use it at home, make
sure it has the three-position "manual/voice/data" switch, so it
doesn't answer your phone for you.

One annoyance: it seems to generate some interference with one of the
local FM stationns (at 90.9 mhz).  Sounds something like a subcarrier
whistling in the background.  Any suggestions for fixes would be
welcome.

Martin Minow
decvax!minow

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Date:     13 May 82 21:34:06-EDT (Thu)
From:     J C Pistritto <jcp@BRL>
Re: Vadic 345x series modems:

	I have had personal experience with around 10 of the new 3451
models (the ones with the voice/data switch up front with the other
two switches) Every one worked right out of the gate, and 8 of them
are used daily for cross country (Baltimore Md to San Francisco, and
Houston TX), with absolutely no failures.  These things are carried
around in peoples brief cases, luggage, etc regularly also.  All were
obtained within the last 6 months, thru a distributer near Washington
DC.

						-JCP-

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Date:     14 May 82 12:54:25-EDT (Fri)
From:     Carl Moore (VLD/VMB) <cmoore@BRL>
cc:       cmoore at BRL
Subject:  "800" prefixes

Interstate "800" prefixes (those not ending in 2) are assigned by area
code (as far as I can tell), as are the intrastate ones (those ending
in 2).  For example, 221 would be NYC from outside NY state.  (This is
as it is now, before the changes I have seen mentioned earlier.)

I do not know how restrictions (other than state-line mentioned above)
are imposed on availability of "800" prefixes via numbering system.

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Date:     14 May 82 12:56:51-EDT (Fri)
From:     Carl Moore (VLD/VMB) <cmoore@BRL>
cc:       cmoore at BRL
Subject:  N0X and N1X in L.A. area (213)

I have list of 213-area prefixes clipped out of a 1976 directory and
such list does include a few "area-code" prefixes. Someone said such
prefixes were put in starting in 1978(?).

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Date: 14 May 1982 12:40:40-PDT
From: eagle!karn at Berkeley
Subject: Mobile radio through ATS-3

ATS-3 is indeed a geostationary satellite.  There was an article on
ATS-1 and -3 about a year ago in 73 magazine, which suggested that
hams might apply to NASA for permission to use channels during off
hours.

There is a demo at the Goddard Space Flight Center Visitors Center
using one of these satellites to demonstrate round-trip propagation
delay.  They use two 10-element yagi arrays, although I don't know how
much transmitter power is used.

In response to 20 watts being sufficient from a mobile whip, here's
the equation for isotropic antennas:

Path Loss (db) ~= 23 + 20*log(d/l)
		where log is base-10
			d = distance
			l = RF wavelength, same units as distance

At two meters, the path loss to geostationary orbit (distance
~=40,000KM) at 2 meters is 169db.

I assumed that the satellite and ground whip antenna have unity gain.
20 watts from the ground would arrive at -156dbW in the satellite
receiver's front end.  If it has a 50-ohm impedance, this corresponds
to .11 microvolts.  Lots of narrow-band FM receivers quiet reasonably
well on .11 microvolts, but the link probably would be marginal. Older
satellites were not noted for particularly good receiver front ends.
Orienting the whip probably helped things.

Speaking of power requirements for satellites, it is quite feasable to
'hit' Amsat-Oscar-8 (a low polar orbiting 2m -> 70cm amateur repeater
satellite) with an audible signal using a standard 1 watt walkie
talkie and its built-in rubber antenna.  It is also very easy to hear
the 300 milliwatt 2 meter FM beacon on Uosat-Oscar-9 with the same
walkie talkie.  Its amazing what you can do with low power when you
don't have the earth in your way!

Phil Karn, KA9Q
Bell Labs, Murray Hill, NJ

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Date: 14 May 1982 1431-PDT (Friday)
From: lauren at UCLA-Security (Lauren Weinstein)
Subject: V&H coordinate tape

I have gotten several requests for information about obtaining the
area/code prefix information tape I mentioned recently.  The person to
contact is:

Pat Jennings
AT&T Long Lines
(816) 391-5708

Ask about the "V&H Coordinate Tape".  The current price is about $50.

--Lauren--

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End of TELECOM Digest
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