[GreenKeys] AP Model 15 information

[sdaitch@ibb.gov]

I never saw any of the polar relays in use with the telco DC loop, but
I admit my experience was with only one AP situation, the radio station in
my home town.  The conversion from DC to tone apparently occurred in the mid-60s or
so.  Maybe the loop length was short enough to use on-off DC.  I do rememeber, tho, that the DC pulses could be heard between the ringing current tones to the station, when you would call them on the phone.  

The Lenkurt system was used well into the 1980s, but I haven't had a good technical discussion with anyone from AP in many years, so I can't tell you how AP is distributing to radio stations these days.  I know the AP was going heavily into satellite distribution, and maybe they are totally off the telco system these days.

The Extel AH series printers had room for and sometimes did have their own tone convertoer buillt in, and it was smaller than the Lenkurt o\box system.

their own 


> On Mon, Feb 23, 2004 at 09:20:22PM -0500, sdaitch@ibb.gov wrote:
> > To the best of my knowledge and feeble memory, the DC loop from
> > the telco was 60 ma, not 20 ma.
> 
> 	That may be correct.   I know that later tty equipment I used 
> interfaced to minicomputers was all 20 ma polar, but I am not sure I
> ever attempted to determine what the loop current was in our college
> radio UPI machine DC telegraph circuit.
> 
> 	It was a polar loop (differential) rather than an on/off
> keyed loop such as that used with the selector magnets on the machine
> and there was a honking old grey cylindrical cased WE polar relay 
> to key
> the actual machine magnet loop from it.     I remember the polar
> relay slowly went bad and we had to have the techs in to readjust it
> back to set points that provided low distortion as copy on the machine
> began to get more and more garbled.
> 
> 
> 
> > 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.  
> 
> 	That matches what the UPI used in our area.   I know it was Lenkurt
> and 25A sound right.   It had two orange neon indicators as you 
> describe,one for carrier and one for the actual data (that flashed 
> on and off
> as the machine printed).
> 
> > 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.
> 
> 	My impression was that it was driven off an envelope detector on
> the output of the narrow bandpass filter for the specific audio FSK
> channel used for that wire.   So if that tone dropped out it would 
> go out.
> 
> 	Of course random line noise might well contain enough energy to
> light it.
> 
> 	I also saw some of the VFT gear used in the early 80s and it
> was considerably smaller (the Lenkurt 25A was rather large for a FSK
> receiver) and looked rather like a small external modem of the 90s
> with LEDs on it.
> 
> -- 
>   Dave Emery N1PRE,  die@dieconsulting.com  DIE Consulting, 
> Weston, Mass 02493
> 
>