[GreenKeys] Telegraph Signal Analyzer
David I. Emery
die at dieconsulting.com
Mon Jun 6 01:11:05 EDT 2022
On Wed, Jun 01, 2022 at 05:57:42PM +0000, Sheldon Daitch via GreenKeys wrote:
> Bob,??
> the answer to your question regarding AP and UPI depended on when.
>
> The radio station in my small hometown in Georgia was an AP subscriber,??and the telco loop was a DC circuit from the central office in town.?? That was 1960.?? ??
> At some point in the mid to late 1960s, maybe even later, the AP wire was converted froma DC circuit from the telco to a tone pack feed circuit.?? ??The AP used a Lenkurt 25 tone??system, up to 25 AFSK circuits on one voice grade channel.?? The Lenkurt unit at the APbureau was a rack mounted unit with the individual tone cards.?? The Lenkurt unit atthe subscriber was a small box, about the size of a shoe box, with one tone demodulatorcard and a power supply for the loop current.
>
> I believe UPI ran the same system.
The UPI tone pack data circuit was installed in 1968 at our
college station and activated about a year later in 1969... Modem was
the Lenkhurt box with orange neon lamps showing power, carrier detected,
and a couple blinking on and off with mark and space...
VFT mux they used used 60 Hz shift FSK with tone CFs at 120 Hz
intervals... modem was indeed about the size of a small shoebox, and sat
on a shelf on the printer table under the model 15.
IIRC those early demods tuned specific channels in the VFT mux
by choice of sets of factory installed filters... later versions used a
superhet architecture which upconverted the 300-3200 Hz audio VFT signal
to a higher frequency IF (around 12 KHz) which the actual channel filter
set was tuned to. This allowed changing the VFT channel by swapping a
fairly large plug in LF LO xtal... or a bit later on by just setting dip
switches that controlled a PLL chip and VCO that synthesized the LO.
Extel printers could be equipped with an internal demod card
based on these principles... so no modem box.
One big advantage of this VFT-mux-to-the-customer distribution
over the earlier telco DC telegraph loops was that all the machines on a
particular wire in a local area served by the same central office were
often connected in series at the CO to make one big polar DC telegraph
loop and if the wire connections to a particular machine at one station
or newspaper was interrupted (say by someone moving the machine to clean
or relocate it) all the other customers lost service. And if the telco
cables to some one machine developed problems (as often happened in some
areas) all the other machines would start to print garbled copy too.
Even changing the polar relay on a machine could kill service for city
on the wire it was connected to unless proper steps were taken to close
the loop first.
And isolating a circuit problem was a bear with all those cables
and polar relays possible causes... when they switched to a voice grade
circuit for distribution it became much easier to isolate problems.
From the 1930s onward (or thereabouts) most of the intercity and
interstate telco telegraph circuits used by the wire services actually
used VFT muxes internally inside the telco with the modulators and
demods (huge rack units with a bunch of power hungry vacuum tubes)
located at the CO and the served machine connected to them by polar DC
telegraph loops.
In the very late twilight days of slow TTY speed printers for
wire service distribution these wire service tone pack VFT muxes were
distributed on satellite signals of various kinds - into at least the
late 90s or so. And in a few places were further distributed on FM SCA
signals for a while.
Today most of this press distribution is done over the Internet...
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
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sets of factory
installed filters. Later demods for these signals used a fairly large
low frequency quartz xtal in a socket to generate a LO for an
upconverting superhet allowing changes of VFT channel by just changing
the xtal... and later ones than that used a PLL chip and could be tuned
with DIP switches or jumpers or BCD switches set by a screwdriver.
>
> Hopefully long past the statute of limitations - in the mid 1970s, I was working for someradio stations in North Carolina.?? Election season and management wanted to do live??reporting from the county elections office and they also wanted the UPI wire at that location.
>
> I had contacted UPI for the cost of a short term circuit to the county elections office andthe price was, well, not within the budget.?? ??I realized that the UPI circuit was a voice gradecircuit from "somewhere" and I just had to local telco establish a copper loop from the??radio station to the elections office.?? ??I jumpered the UPI tone pack audio over to the??loop, picked up the UPI Extel printer and a roll of paper, took it over to the elections??office and it worked fine.
> 73SheldonWA4MZZ
>
>
>
> On Wednesday, June 1, 2022, 12:31:57 PM EDT, Robert Nickels <ranickels at gmail.com> wrote:
> When I worked at radio stations in high school and college, we'd routinelyorder up dedicated lines from the telco for special broadcasts, but that
> was audio, and you'd pay for the duration the circuit was up. ?? The AP
> or UP and weather teletypes ran from permanent lines (provided by the
> telco too I think) -?? but those had to be copper, right??? Or did they
> send audio and convert it to current loops at the machine????????? There
> would obviously be a limit on how far they could run a current loop
> signal, so it would make sense to convert to audio tones, or they use
> some sort of regenerator????????? I would guess that local telcos
> distributed the signals on behalf of the originator (i.e. UPI, AP,
> National Weather Service, etc) to the radio and tv stations, newspapers,
> etc who subscribed to those services.
>
> I remember there being interface boxes on the wall but never knew what
> they actually did.???????? My only concern was to make sure the machines
> didn't run out of paper so you'd have something to "rip and read".
>
> 73, Bob W9RAN
>
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--
Dave Emery N1PRE/AE, die at dieconsulting.com DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
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