[GreenKeys] AP Model 15 information

[sdaitch@ibb.gov]

To the best of my knowledge and feeble memory, the DC loop from
the telco was 60 ma, not 20 ma.

The tone carrier equipment used by the AP in GA, SC and NC, for sure and 
probably the rest of the nation, was the Lenkurt 25A system.  The equipment at the
AP bureau sites were the rack mount versions, for the full tone pack access.

The subscriber units were a single channel tone decoder, for one of the service channels, and contained a DC loop supply.  There were two neon bulbs on the
front of the unit, actually a recessed panel, one was lit if there was an audio signal on the incoming VF phone line.  The other lamp keyed with the loop current.  

I don't think the signal lamp acutally was a test of a valid tone pack signal, but triggered by any audio on the phone line, and a noisy phone line would give a false good signal.

I seem to recall the funny AC power cord, but I think it was simply the base of the
printer to a junction box in the table stand, and there was another conventional cord to the wall outlet.

Sheldon
WA4MZZ


----- Original Message -----
From: Dave Emery <die@dieconsulting.com>
Date: Monday, February 23, 2004 2:03 pm
Subject: Re: [GreenKeys] AP Model 15 information

> On Mon, Feb 23, 2004 at 12:08:22PM -0500, Dan Beach wrote:
> > 
> > I have recently acquired a Model 15 which was used by the 
> Associated Press.
> > It appears to have a straight 120vac power connection (although 
> the plug is
> > the 3-pin  connector in Y-layout, usually associated with DC), 
> along with a
> > red/green pair which went to the phone line connection. In 
> addition, there
> > is a panel in the rear of the machine I've never seen before 
> which has a
> > transformer, capacitor and various  diodes and ic's.  Does 
> anyone know if I
> > am safe assuming that this is the loop power supply? And if so, 
> what would
> > have been the signal provided thru the phone line to trigger the 
> relays?> Just polarity reversal?
> > 
> 
> 	In the mid 60s most wire service (AP, UPI, Reuters etc) networks
> were converted from DC +-20 ma telegraph circuits to VFT multiplex 
> audiotransmission of the tty data.   These consisted of up to 24 
> channels of
> low speed FSK signals FDM multiplexed together in a 3.2 khz one 
> way 
> audio channel (VF data circuit).
> 
> 	It rather sounds like you have one of the modems for that.
> 
> 	The standard used by the AP was 120 hz between channels and
> around 60 hz FSK shift with the lowest channel starting at 420 hz.
> 
> 	This technology was in use at least into the mid 80s and AFAIK
> may have seen service even after that in some areas.
> 
> 	Prior to this conversion, wire service circuits were distributed
> by more antique Telco based VFT equipment to local private line 
> centersand then distributed by DC loops to the customers.    And 
> it turns out
> that if there were multiple customers served by one CO they put the
> loops in series.    I discovered this back in the 60s when we 
> tried to
> move our college radio station wire service machine and 
> disconnected the
> loop and got panic calls from the local TV station that their UPI
> service  was dead...
> 
> 	In addition to avoiding that problem, the VFT mux system allowed
> multiple circuits to be installed at low cost - for newspapers for
> example that might have a sports wire, a national A news wire and 
> and a
> local area news wire.
> 
> 	Later on in the 70s the wire services took to transmitting
> material via 1200 baud 202 FSK modems (the basic modem standard 
> ham AFSK
> packet uses) to newspapers with early computerized text 
> processing.   
> Then in the 80s and 90s much of this went to satellite 
> distribution and
> now a lot is via the Internet (VPNs and so forth).
> 
> -- 
>   Dave Emery N1PRE,  die@dieconsulting.com  DIE Consulting, 
> Weston, Mass 02493
> 
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