[GreenKeys] AP Model 15 longevity

[wa2hwj at att.net]

With all of this satellite sophistication, I am contiually amazed that the Canadian Forces
still broadcast 100 wpm Baudot weather on HF radio! Does anybody have any
insight into this operation? The signal comes from Nova Scotia and the ID
header is "CANADIAN FORCES METOC CENTRE..."  The TTY weather is sent
on the half hour (give or take) and it's usually comprised of airport observations,
with some plain text forecasts, iceberg reports and bouy reports...fascinating!
I've been copying this station for years. 

Re: 15's versus 28's...a 28 running at 60 wpm would probably outlast a 15
since it doesn't have the felt clutches. Ma Bell ran their 15's at 75 wpm in the 80's
and those poor machines just kept chugging away, but they  needed a lot of
TLC to keep them going. They were replaced with 28's and 35's  for a short time and then
all of the TTY's disappeared. 

73,
Jack WA2HWJ



-------------- Original message from "David I. Emery" <die at dieconsulting.com>: -------------- 


> 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." 
> 
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