[GreenKeys] AP Model 15 longevity

[David I. Emery]

On Mon, Sep 24, 2007 at 02:32:30PM -0400, Larry Tighe wrote:
> Hi Sheldon et. al.,
> 
> Here's the skinny on AP today.  We have a small, about 24 inches, sat dish 
> for AP.  That goes to a receiver and what looks like a "modem" fed by the 
> rcvr.  The modem connects to other  PC's.  We had to go find the AP 
> receiver....it's burried under junk behind a desk in the newsroom!!!

	At one time about 15 years ago AP was on a C band signal on one
of the commercial communication satellites.   At least one of those
signals was a 56 Kbs QPSK signal (or maybe 112 Kbs I forget) with a
variety of things digitally muxed on it.   Very powerful SCPC signal
that basically was the only thing on a whole 36 MHz transponder (I think
there were a couple of other weaker signals, but most of the power was
in this one signal making it *lots* stronger than other similar narrow
band digital SCPC signals on satellites).

	Dishes were about 5-6 feet and not 24 inches and most newspapers
around Boston seemed to have them - not sure about radio stations and
whether they used this system or not.

	There is also another C band small dish system that has been
used in the past for wire services - namely the very early pioneering
spread spectrum system built originally by Equatorial Communications.  
This uses a 4 MHz wide BPSK spread spectrum transmission carrying a QPSK
signal at a couple of different rates (19.2 Ksym/sec  in the original
system I remember) which contains  multiplexed low speed TTY circuits of
the sort wire services used for many years.    The spread spectrum DSSS
stuff allowed them to transmit a lot of energy without exceeding the
carrier level in any narrow band that might cause interference to the
then common (but now obsolete) 4 GHz telco FM-FDM microwave signals. 
And the lots of energy allowed the system to work with tiny C band
dishes as small as around 24 inches or even less.

	For quite a few years in the 1980s and early 90s these
Equatorial systems were common for wire service and other broadcast TTY
networks, but I think time has marched on and most of them are now gone
(at least I don't see many on buildings).   They were very easy to spot
since the dish was prime focus fed by a C band waveguide splash feed
(waveguide sticking up in the middle of the dish with a little round
reflector on the end of it).   Most current small dishes (all Ku or Ka
band these days) are of course offset fed with the feed below the
reflector and off to one side so the equatorial dishes stood out as they
looked different and seemed to be facing different since offset fed
dishes don't directly point at the  satellite they use.

	In addition to the unusual mini C-band dish, the Equatorial
systems had a big honking downconverter behind the dish (about a 10 inch
by 10 inch by 1.5 inch think box) which looks unlike anything current
(LNBs and even uplink BUCs are mounted at the feed of modern Ku dishes).
And the unit that goes inside for the Equatorial system was a large box
19 inches wide by about 20 inches deep by about 6 inches tall.

	Of course as several readers of greenkeys know, the AP and UPI
and Reuters switched from DC telegraph circuits (mostly polar 20 ma) to
dedicated voice grade lines carrying "tone pack" VFT signals with each
different "wire" on a different FSK tone pair (usually 60 hz shift and
120 hz channel spacing for low speed stuff) in the late 60s.   For quite
a few years thereafter the various wire services operated extensive
national networks of voice grade one way circuits carrying this VFT mux
and newspaper and radio stations received it and had one or more
Lenkhurt (or later other including OEM versions built into Extel
printers) boxes that decoded a specific tone pair and drove the 60 ma
TTY loop.   The basic idea was that one circuit could supply multiple
newswires to a newspaper or larger radio/TV station without  requiring
multiple wires and connections.

	If one was a suitable hacker back then, one could sometimes come
by the VFT signal and decode other wires.   And at least briefly in a
few places this signal was stuffed on SCA subcarriers of radio stations
as a means of distributing the service, but I don't think this lasted
very long.

	The big wire services also supplied most of their content in
that era (70s and later) as 1200 baud 202 (AFSK) circuits carrying
ASCII.  Up to date newspapers of the era fed this into early computer
based editing and photo-composition systems based on CRT terminals and
later PCs.   The messages on these 1200 baud circuits were in a
standardized format so software could easily sort out and store in a
database the stories for later use by reporters, editors and on the air
news anchors.

	And I guess by the 80s some time satellite transmission of both
the high speed and low speed circuits became so attractive that most or
at least much of the extensive voice grade leased line network got
replaced.   I am not sure when the last of it was turned down.

	For quite a few years UPI transmitted their VFT signal carrying
radio station TTY newswires on a SCPC FM carrier on a satellite, but I
think they have since replaced this with some more sophisticated fully
digital transmission scheme.   I am not sure anyone any longer transmits
wire copy as low speed 45 or 50 or 75 baud signals - I think everything
out their has migrated to faster (and ASCII) transmission - but I could
be wrong as I haven't kept up with this area.

	As for the current AP stuff I have lost touch a bit... it
certainly would be easy enough to stuff a 1200 baud 202 signal into an
audio channel of some one of the Ku band signals used to distribute
Muzak and similar background music as Musicam MPEG 2 audio over QPSK DVB
transport streams and this  could result in a configuration with a
"receiver box" that is just a standard Wegener or similar QPSK MPEG
audio receiver feeding its audio output for one dedicated channel into a
202 modem and from that into a PC.   This would obviously result in a
configuration with a "receiver box" attached to a "modem".   And the
muzak systems use small dishes in the order of 24 inches to 1 meter
depending on how much rain fade margin is felt necessary and how strong
the satellite signal is.   And obviously too a higher speed than 1200
baud could be used, even over a Musicam audio channel.

	But there are lots of other configurations possible and at least
I would be curious as to the details of what is used at your radio
station so as to keep my mental file on the subject up to date.  What is
the make and model of the receiver box and what is the make and model of
the modem ?

	And a final comment slightly more germane to this thread - my
personal experience back in the 60s was that model 15s were a LOT more
rugged than model 28s... they just seemed to keep going and going and
going... model 28s, especially at 75 or 100 wpm would not...

-- 
  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."