[GreenKeys] Re: M20-RO

[Sheldon Daitch]

Jack,

OK, maybe it was a Lenkurt 25A system.

As I recall there were two basic setups, the
single subscriber module and the point to point
full sized multiplex (MUX) system.

The shelf mounted unit (actually a self contained
box) that went under the printer unit was a single
channel receiving unit for the system.

At the AP regional bureaus, they had the full fledged
rack mount system.  It was somewhat modular,
tho, and each tone transmit and tone receive system
used a separate module.  Again, going from memory,
I think the channel frequency plan was the standard
16 channel tone pack, but I really could be wrong on
this.  Normally, the bureau unit had mostly transmit
cards, with perhaps a few receive channel cards, but
it generally was not a balanced system, i.e., the
transmit and receive channel capabilities were not
equal.  (On second thought, maybe there were
receive cards for each transmit channel if for
nothing else, to monitor each outgoing TTY circuit.)

As best I recall, in the early 1960s, the AP tail circuit,
from the telco office to the subscriber, was a DC loop.
How the telco got the TTY signal from the AP bureau
city to the local end office, I don't know, but I can only guess
the phoners had some type of MUX equipment.

I can only image that between Lenkurt marketing a TTY
multiplex system, the AP needing to expand its distribution system
and the phoners raising the tariffs that the AP decided to get the
phoners out of the DC network, and simply lease a voice
frequency grade distribution network that was much easier to
handle than what had to be done with the DC tail circuits.  I think
this transition occurred somewhere in the mid to late 1960s.

Another savings could have been that from an AP bureau to
the telco facility, there was a DC loop for each outgoing
TTY circuit and with the tone MUX, only one VF grade
audio pair was necessary.  I suspect money was really the
driving force at that time.

The Lenkurt system worked fine at 60 to about 75 wpm
but I think it became marginal in trying to run 100 wpm.
I believe there was one channel, maybe a weather crawl
for cable TV operators, that was on the ragged edge of the
capabilities of the Lenkurt system.

73

Sheldon



wa2hwj@att.net wrote:

> I looked a little closer at the Lenkurt...it is a System 25A unit and the
> label on the front is a United Press label, not AP (I got it from
> an old AP guy and assumed it was from AP!). It does have the filter
> and seems to function well according to some testing I did on it a few months
> ago.
>
> Jack WA2HWJ
>
> NNNN
> >
> >
> > Jack wrote:
> >
> > > I have one of the Lenkurt tone receivers with the
> > > Associated Press emblem on it. I believe it receives
> > > at 85 HZ shift. It has a built-in loop supply. As far as I can
> > > tell, it was wired directly to the incoming telephone circuit and
> > > the TTY was plugged into the loop jack.
> > >
> > > Jack WA2HWJ
> > >
> >
> > I have two of them with UPI emblems. They make really nice standalone
> > loop supplies now with (i think) terminals 3 and 6 on the back panel
> > jumpered.
> >
> >
> >
> >
>
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