💾 Archived View for gemini.spam.works › mirrors › textfiles › messages › BACKWATER › bw830506.txt captured on 2022-06-12 at 15:42:07.
-=-=-=-=-=-=-
NUMBER OF LINES: 629
1 If you are in need of help, you need but ask....
2 ********************* REMOVED: 6 MAY 83 *****************************
3 Welcome to BWMS (BackWater Message System) Mike Day System operator
4 ************************************************************
5 GENERAL DISCLAIMER: BWMS IS NOT RESPONSIBLE FOR ANY INFORMATION PLACED ON
6 THIS SYSTEM.
7 BWMS was created as an electronic bill board. BWMS is a privatly owned
8 and operated system which is currently open for use by the general public.
9 No restrictions are placed on the use of the system.
10 It is intended that the system be normally used for messages and
11 advertisments by the users. As the system is privatly owned, I retain the
12 right to remove any and all messages which I may find offensive
13 to me. Additionally because of the limited size of the system, it will be
14 periodically purged of older messages. (only 629 lines of data can be saved)
15 The saved information will be cycled to drive 'B' while the information on
16 drive 'B' will be archived, and a fresh disk will be installed in drive 'A'.
17 To leave a message, type 'ENTER' and use ctrl/C or break to get out
18 of the enter mode. The message is automaticly stored.
19 If after entering the message you find you made a mistake,
20 use the replace command to replace the line.
21 To exit from the system, type 'OFF' then hang up.
22 Type 'HELP' to see other commands that are available on the system.
23 ========================================
24
25 About the hang-up sequence, you should not read into the specifications
26 that which is not there, yes, in some modems they will hangup if they
27 receive a 'long space' or loose carrier, but there is nothing that says
28 they must. The Hays manual says that it will, and indeed it will. BWMS
29 will also hangup if it looses carrier for about 10 seconds. It does not
30 support hanging up upon 'long space' however. If you are going to expound
31 non-standard standards based on most of the modems that the hobbist
32 community encounters does it therefor it is standard, then keep in mind
33 that most modems of this sort will hang up on their own upon the user
34 droping the RS232 DTR line (pin 20). Interestingly enough many modems
35 have this strapped out because the equipment it is hooked to is not
36 inteligent enough to handle this. Also as I remember, there was a
37 command in the Smart modem which told it to hang up anyway.
38 How about it P.G. do you remember what it was? As I remeber there
39 was some weird sequence involving an '@' and a time delay or something.
40 But anyway there is nothing that says that the answer modem 'must'
41 hangup via anything, some modems do provide certain ways of doing
42 this however, and BWMS will hang up if you turn off your carrier,
43 or if you hang up your modem.
44 Having been in the communications field for the last 8 years, I think
45 that I should know a little bit about this aspect.
46 ......................................................................
47 WE NOW HAVE BLUE AND PINK SOFTWARE ON THE MARKET-JUST STATE YOUR CHOICE
48 AND THERE WILL BE NO PROBLEM IN FILLING THE ORDERS. THE O.J.KID........
49 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
50 The "standard" (hang-up on long space) may not be standard with
51 all equipment, but a number of manufacturers think it is a true
52 standard & build their equipment accordingly. (and then they
53 write software that won't allow me to send a continous space!!!
54 ARRRGGGHH!) I'm not an expert but I got the impression from my
55 modem's documentation that the manufacturer thought that the
56 long space hang-up was part of the Bell-103 standard!
57 Oh well, so it goes.....
58 _________________________Leonard_______________________________
59 The Hays Smarmodem uses '+++' after a second of steady
60 marking to give back the command state. Then you can enter 'AT H' to hang
61 up. Many modems allow one to selectively enable the long space disconnect.
62 I use it to provide a hardware reset for my computer when I am remotely
63 accessing it. Needless to say, when you talk to CBBS and you forget to
64 disconnect the reset function, you have to reboot when you sign off with
65 Bill and Jims's machine!
66 Regarding women in computers. My wife has been taking programming
67 classes for a couple of years now, and she just got a job as an programmer
68 trainee with the company for which we both work. Although she is now
69 reading an exciting book on System 370 JCL, she has almost no interest
70 in my microcomputer as a hobby device. The section of the department
71 she is to work in is almost all women programmers (except for the
72 supervisor!). There surely is no hiring bias against women, and there
73 may even be a pro-female leaning in the business programming area.
74 Could it be that women are less masochistic? Why would a sane
75 being want to abuse himself (or herself) by dealing with the same set
76 of frustrations all day a-n-d all night? It must surely be associated
77 with the type of hobbies that men and women prefer. Dealing with
78 machines is in vogue for women on the job, but the cultural biases
79 still place women's off the job interests elsewhere. (I'll always
80 remember the comment of a woman bicyclist I knew in California. We
81 both were on a 100 mile tour and had just reached the top of a hill
82 with about a 1000 foot rise in elevation. She remarked, "I always
83 thought masochism was a MALE word!")
84 If providing recyclable bottles is so expensive, why are the
85 soft drinks in the glass returnable bottles always the least expensive,
86 when compared to the aluminum and plastic containers?
87 If I have missed any of the current topics of discussion (except
88 VG's), let me know and I'll bore you on that, too...
89 {}{}{}{} Analog Alan, Telecom Engineer, Male, 34 {}{}{}{} April 18 2015 PST
90 LEONARD:
91 THE 'LONG SPACE' DISCONNECT IS A HOLD OVER FROM (BELIEVE IT OR NOT) THE
92 OLD MECHANICAL TERMINAL DAYS. YOU SEE IN THOSE DAYS THE ONLY WAY TO GET
93 THE MACHINE TO HANGUP WAS FOR THE PHONE LINE CURRENT TO REVERSE. AND THE
94 ONLY WAY TO GET THE PHONE LINE CURRENT TO REVERSE WAS FOR THE OTHER END TO
95 HANGUP. BACK THEN THEY DIDN'T HAVE THESE NIFTY THINGS CALLED
96 MODEMS. SO THEY HAD TO RUN DIRECT CURRENT ALL THE WAY TO THE COMPUTER.
97 NOW SINCE SOMEBODY HAD TO HANGUP, THEY HAD TO FIGURE OUT A WAY TO DO IT.
98 THE WAY IT WAS DONE WAS TO ADD A 'BREAK' KEY TO THE MACHINE. WHAT THIS DID
99 WAS SIMULATE WHAT YOU DO WHEN YOU HANG UP THE PHONE, YOU 'BREAK' THE
100 CONNECTION. THIS THEN CAUSED THE EXCHANGE TO RECOGNIZE THE HANG UP,
101 AND SEND THE REVERSE CURRENT TO BOTH PARTIES SO THAT THE MACHINES
102 WOULD DISCONNECT FROM THE PHONE LINE. WELL, AS DISTANCES INCREASED AWAY
103 FROM THE CENTRAL COMPUTER (OR OTHER TYPE MACHINE) THE DIRECT CURRENT
104 METHODE DIDN'T WORK TOO WELL, SO MA BELL CAME UP WITH THE MODEM TO
105 TAKE CARE OF THE PROBLEM. WELL, NOW A NEW WRINKLE WAS ADDED, SINCE THE
106 MODEM WAS ON THE PHONE LINE INSTEAD OF THE MACHINE, THE BREAK KEY
107 DIDN'T WORK ANY MORE. WHAT IT DID DO THOUGH WAS THAT WHEN IT WAS
108 DEPRESSED IT CAUSED A CONTINUOUS 'SPACE' TO BE SENT OUT THE MODEM
109 (THIS WAS A RESULT OF THE CHARACTERISTIC OF THE WAY THE CURRENT LOOP
110 WORKS). SINCE THERE WAS NORMALLY ONE COMPUTER FOR THE DOZENS OF
111 TERMINALS OUT THERE IT WAS DECIDED THAT IT WAS UP TO THE COMPUTER TO
112 FIGURE OUT THAT THE LONG SPACE WAS A DISCONNECT REQUEST AND TO HAVE
113 SOME WAY TO HANG UP THE PHONE LINE AS A RESULT. WITH NEWER EQUIPMENT
114 THIS IS NO LONGER A REQUIREMENT, BUT THE ABILITY IS OFTEN MAINTAINED
115 SO AS TO HANDLE THE OLD CLUNKERS. MOST COMMERCIAL MACHINES ARE SETUP
116 TO SEND THE LONG BREAK JUST IN CASE, AND THEN FOLLOW UP WITH A DISCONNECT
117 ANYWAY JUST TO BE SURE. THE REASON HERE IS THAT IF THE COMPUTER FOR
118 SOME REASON (AND THERE ARE MANY!) FAILED TO SEE THE LONG SPACE IT
119 MIGHT NOT DISCONNECT, AND IF ITS A LONG DISTANCE CALL YOU COULD RUN
120 INTO A HEALTHY PHONE BILL BEFOR IT WAS CAUGHT. THE EQUIPMENT SOMETIMES
121 ALSO HAS A 'NO ACTIVITY' TIMEOUT AS WELL FOR ADDED INSURANCE.
122
123 AT ANY RATE, IT IS NOT WISE TO RELY ON A LONG SPACE DISCONNECT OR
124 COMMANDED DISCONNECT TO WORK EVERY TIME PARTICULARLY ON LONG DISTANCE
125 CALLS WHERE IT COULD BE EXPENSIVE. THE BEST WAY TO BE SURE YOU ARE
126 DISCONNECTED FROM THE LINE IS DISCONNECT IT YOURSELF. THAT WAY EVEN
127 IF THE OTHER END BLEW UP AND HUNG ON THE LINE YOU WON'T BE CHARGED
128 FOR ANY MORE TIME BECAUSE YOU ARE NO LONGER ON THE LINE.
129 *** JUST A FEW THOUGHTS FROM CISTOP MIKEY *** 19 APR 83 ************
130
131
132
133 A liottle note from USA TODAY, dated april; 18,83:
134 engineering schools are now about 3.6 % women, up from under 1/2 %
135 ten years ago. Women in science related jobs tripled between 73 and 77,
136 and doubled again from 77 to 81.
137 However, it is interesting to cogitate on the numbers of where they
138 go. Physics 5%; mathematics 12%; chemists 14%; biologists 20%;
139 psychologists 45%.
140 In physics, where facts are strictly compared with reality, women
141 are rare, but in psychology, where facts are rare, and opinion strong
142 (along with insanity) women are more common. Perhaps women dislike
143 hard science, and are more at home with soft, social stuff.
144 ++++++++++++++++++++++++++++++++++++++++++++B.A.D. apr-19-83 2357pm++++++
145 Way back before intelligent ESS's, you could 'pin' someone's phone so
146 as to be unusable by calling it, waiting for someone to answer, and
147 never hanging up. No matter what they did, the phone was semi-
148 permanently locked up. My school's dorm phone system was based on
149 just such machinery.
150 With modern equipment, it isn't possible to do this. Either
151 party can hang up and the connection will be broken.
152 Interesting aside: If the 'called' party hangs up, but the
153 'calling' party stays on line, the connect isn't actually broken for
154 about 13 seconds. If during this period the called party picks up
155 the phone again, the connection is still maintained. Even if the
156 called party only very momentarily picks up the phone (.5 seconds, for
157 example) this delay occurs. I don't know if that will constitute
158 a billable call (maybe will try this) but if not, a free computer-
159 to-computer connect can be kluged up: Computer A calls Computer
160 B. Computer B 'picks up the phone' for .5 seconds. 'Hangs up'
161 then, but still listens and talks to the line. 13 seconds of communication
162 are then possible.
163 At 300 baud, that's 30 CPS, or about 1000 characters total
164 per connect. Possibly free! Who knows. With all of this talk about
165 electronic mail, such a system would be a tremendous benefit to nearly
166 everyone but the phone company.
167 Reach out and touch someone's baud.
168 ................................................................
169 In regard to the above I wonder how much of this "modern" equip-
170 ment is in service. About 3 years ago I made a call from a
171 231 # to a 235 # & didn't get the phone hung-up properly. The
172 friend who's BUSINESS I had called had to drive over and tell me
173 that I had his phone "trapped". So as I said, which exchanges
174 have this "modern" equipment & which don't?
175 As to cheap data transmission, I have read of a modem
176 that will operate on a NORMAL RESIDENCE LINE at 9600 baud!!!
177 It will only run half-duplex (take turns transmitting) but at
178 that speed who cares? It use a VERY non-standard format but I
179 am going to look into it, especially since the price is about
180 $100!!! (let's see now- 60 sec at 9600 baud = 57600 bytes....
181 _________________________Leonard____________________________
182 THE OLD STUFF IS DISAPPEARING PRETTY FAST: 43,000 LINES LAST FRIDAY
183 NITE, ABOUT 25,000 MORE IN THE 233, 234, 235, 237 GROUP LATER THIS
184 YEAR, ANOTHER 15,000 LINES IN THE 282, 288 EARLY NEXT YEAR, AND THEN
185 THERE IS NO MORE STEP BY STEP IN PORTLAND. (IT COSTS TOO MUCH TO
186 MAINTAIN)
187 --------------------------------------------B.A.D.-------------------
188 LEONARD:
189 ABOUT THE 9600 BAUD MODEM, IT SOUNDS LIKE A LOCAL AREA MODEM TO ME.
190 THEY HAVE BEEN AROUND FOR SOME TIME, AS LONG AS YOU DON'T GO THRU ANY
191 OF MA BELLS AMPLIFIERS OR FILTERS THEY WORK GREAT. THE ONLY PROBLEM IS
192 THAT IF YOU DON'T GET SPECIAL PREMISSION (A PRIVATE LINE) MA CAN GET
193 VERY UPSET IF SHE FINDS OUT. THIS IS BECAUSE THEY TRANSMIT HARMONICS
194 OUTSIDE OF THE ALLOWED RANGE. THIS ALSO MEANS THAT IT CAN'T GO THRU
195 THE NORMAL SWITHING NETWORK. THAT IS IT WILL ONLY WORK POINT TO POINT
196 NO CALLING ALLOWED. THEY DO THIS BY SIMPLLY TYING THE PAIRS TOGETHER
197 AT THE EXCHANGE. I HAVE HEARD OF A 9600 HALF DUPLEX MODEM THAT WOULD
198 RUN ON THE DIAL NETWORK, BUT IT WAS $10K NOT $1K, AND EVEN THEN IT
199 DIDN'T WORK EVERYWHERE (IT GOT FOULED UP GOING THRU DIGITAL REGENERATORS.
200 ........ CISTOP MIKEY HERE .......... 20 APR 83 .....................
201 It's amazing how much old telephone equipment is still in use. Or perhaps
202 not amazing, since it is a very capital-intensive business. Until about
203 10 months ago I was on Step-by-Step, and it sucked. (pardon my French)
204 Old news from Ma Bell: Business users will have access to
205 a direct digital transmission system within the next few years. It's
206 at 56K baud, and is based on the fact that this is the effective data
207 rate of voice communications. Will this kill modems? Ultimately,
208 yes, but it will be a while before the ordinary mortal will be able to
209 access this system. Sigh...
210 And here I am, stuck at 300 baud.
211 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
212 That 56k direct data is not switched, but on very special private
213 lines, point to point only: the switched service is not yet available.
214 It isn't 56k only, if you have use for it, it goes to 1.54 megabaud.
215 Sorry, as to the old step by step in Portland, I forgot the Cyupress
216 area 292, and 297- which does seem to be in Portland, too It goes out
217 on about mid 1985, if the schedule is kept. Of course, it wasn't too
218 long ago they were saying 1980.
219 Modems will always be with us, at least until the phone net becomes
220 digital from the phone itself: this is the only cheap way to get
221 full access. If 300 is too slow, go to a Portland Computer Society
222 meeting and buy a 1200 baud modem. (202 type) Talk to Roger Giles.
223 ######################################################B.A.D.######
224 If you don't ask Mike who developed the PCS modem (which works at
225 both 300 and 1200) , I suppose somebodey should say: he did it, ie
226 Mike.
227
228 To connect a plain vanilla phone to a KTS type 50 pin plug, the easiest
229 way is with a Radio Shack part no 43-270 or 43-271. I don't know if the
230 bell will work with these, probably not. In theory, if you connect
231 ANYTHING to the phone lines, you must inform the phone company, and
232 it must be registered, but we all know if you keep it reasonable.....
233 ............................................................
234 SOON TO BE AVAILABLE - A SOFTWARE PACKAGE THAT ALLOWS FULL USE OF
235 HALF DUPLEX MODEMS OR COMMUNICATIONS LINKS (I.E. RADIO) IT IS ALSO
236 COMPATIBLE WITH THE EXISTING MODEM PROGRAMS RUNNING AROUND FOR
237 THE CPM SYSTEMS. THIS MEANS YOU WILL BE ABLE TO USE THAT HIGH SPEED
238 SYNCHRONOUS MODEM AT 2400, 4800, OR EVEN 9600 IF YOU CAN STAND THE
239 PRICE OF THE PHONE SERVICE AND MODEMS. IT ALSO RUNS WITH THE PCS-103
240 MODEM AT 300 FULL DUPLEX OR 1200 HALF DUPLEX. I WILL KEEP YOU POSTED
241 ON THE DEVELOPMENTS HERE AS THEY OCCUR.
242 ................................................................
243 On checking back, I see that it was 4800 baud - not 9600. But
244 WAS for use on normal voice lines & the price was supposed to
245 be ONE HUNDRED (100) dollars NOT $1000! But it is TOTALLY in-
246 compatible with the various Bell & Vadic standards. I didn't
247 completely understand the explanation, but it sounded like D/A
248 conversion of some sort, not really modulation at all! As I
249 recall they seemed to be saying that it was converting the mark
250 signal to a frequency inversely proportional to its duration
251 (and they are using half-cyles!). Maybe it qualifies as some
252 sort of phase modulation? The low price is probably for OEM
253 quantities, since they are aiming at the bank-at-home market &
254 other similar markets where a CHEAP terminal is needed. I've
255 got to try and find that file again & write them. I THINK it was
256 "The Peripheral People" or Micro-Peripheral Corp. (whichever is
257 based in Washington state).
258 As for my multi-line problem, what I want to do is hook
259 to "normal residence lines" to one "normal" phone. At present
260 I'm using a rube-goldberg hook-up consisting of a Radio Shack
261 43-271 4-line tap (it's been discontinued but a lot of stores
262 still have them!) connected to a 43-233 multi-line controller.
263 It's a bit weird, but it works. The phone rings on whichever
264 line the button is pushed for. I just wonder if there is a
265 better way (also- will Ma Bell object if she finds out?)?
266 Any ideas??
267 _________________________Leonard_____________________________
268 =======================================================================
269 Leonard:
270 As I remember it was Micro-Peripheral Corp. I remember that ad too.
271 I haven't seen it since, maybe they found out it didn't really work?
272 While 4800 is possible via the method you indicated, it can tend to
273 fall apart if it goes thru some of Ma's filters, or is a long way
274 away from the exchange, the problem is that the bandpass of that kind
275 of signal is horendous and is difficult to handle in those kind of conditions
276 that is not ot say it can't be done, just that there can be problems.
277 a very big one is the harmonics it generates into ma's lines which could
278 get her a bit ticked off if it isn't filtered out (more money to filter
279 that stuff). Most modems use phase shift (dibit or tribit) to run up
280 there as it is more reliable and easier to filter. but it is still
281 expensive alas. maybe in the near future this will change what with
282 the new single chip modems hiting the market now....
283 ***** CISTOP MIKEY ******* 22 APR 83 ******************************
284 A few comments on what a modem needs to comunicate:
285 A binary modem needs at least 1/2 as many hertz bandwidth as bauds, i.e.
286 a perfect modem running 300 baud could fit in a bandwidth of 150 hertz.
287 Reasonable filters and detectors, however about double this, so figure
288 about bauds=hertz. Cheaper systems need more bandwidth, and to allow
289 for variations in the signal (both noise and distrtion, as well as
290 frequency sensitve effects of the line) you had better allow more yet.
291 The telephone lines will allow about 400-2700 hz, or about 2300 hz
292 bandwidth, but don't depend on the edges of that, figure maybe 1800 or
293 2000. This seems to allow for 3600 baud, or if you wnat full two way
294 communications (full duplex) about 1800. The 212 from Bell or equal
295 from Vadic will do this, but they are pricey. Allowing more space between
296 the up and down bands, and simpler filters brings you down to 103 type
297 modems at 300 (two way), or modifying this up to 600 baud (sometimes),
298 or 1200 bauds oneway with 202 modems.
299 The faster or the closer you are to the limits of your modem the more
300 sensitive you will be to noise or line distortion.
301 It also doesn't make much difference whether you use AM, FM (103 or 202),
302 or phase modulation (212), the essential bandwidth is the same at the same
303 speed of data. PM, however is less sensitve to the types of distortion
304 phone lines, and their repeaters have. (It isn't as good for say, tape
305 recording data, because this has jitter.)
306 You can however encode more than one piece of data into each change,
307 and thereby send data faster than you change signals, to get higher
308 data rates over a low speed line. The fast modems aren't binary, but
309 use 4 or more discrete levels such as different phases, or change
310 both phase and level simultaneously. This of course makes the detecting
311 problem much harder, and more sensitive to noise and distortion, so to
312 make up for it the really fast modems run even faster than they pass
313 data, and use the difference for checksums or retransmissions of errors.
314 This works because the phone noise is usually hits or pulses, with
315 clear time in between.
316 Pushing the limits won't usually work, because the phone companies use
317 digital transmission (carrier) systems between offices, and these are
318 sharply filtered to prevent distortion, as well as automatic level
319 controls to improve the signal to noise. (Digital systems have something
320 called 'aliasing' that changes a high frequency into a low, annoying one.)
321 Within one exchange area, though you can usually get away with murder,
322 because at present nearly all phone switchers are fully analog.
323 It is especially important to avoid 2600 hz, because this is the
324 disconnect signal for long distance circuits.
325 Since the phone lines are designed for voice, they have rather poor
326 frequency response, both cutting off the bass and treble ends, and
327 what is worse from a data standpoint, the phase shift is not controlled.
328 To reduce high frequency losses, the lines are 'loaded' with inductors,
329 but this causes severe phase shift instead. You can't hear it, but it
330 plays havoc with data pulses. Carrier systems may also cause phase jitter.
331 4800 or even 9600 is now fairly common, though, even over uncontrolled
332 dialups (if it doesn't work on one connection, hand up and try again)
333 but the gadgets that do it aren't cheap.
334 KEEP AT IT, MIKE WE NEED THAT 202 PROTOCOL. 1200 baud is 4 times as fast,
335 and really we don't usually need full duplex.
336 Just a thought, in Europe they are using a system that is 1200 baud
337 from the computer to you, and 75 the other way, full duplex.
338 ~~~~~~~~~~~~~~~~~~did I hear an "AARRGGHH??"~~~~~B.A.D.~~~~~~~~
339
340 HELLO;
341 SO , THIS SEEMS TO BE A NICE BULLETON SYSTEM!
342 IF POSSIBLE, YOU MIGHT WANT TO LIST OUT PHONE NUMBERS
343 OF OTHER SYSTEMS.
344
345 THERE IS A "END OF THE WORLD" SALE OF FIFTIES, SIXTIES RECORDS, NICK -
346 KNACKS, WHAT NOTS, THINGAMAJIGS********SAT.24,1983 AND 4/30/83 TO
347 CONCERNING THE END OF THE WORLD SALE-THE ADDRESS IS 5933 NORTH ALBINA
348 $$$$$$$$$$$$$$PORTLAND , OREGON $$$$$$$$$$$$$$
349 ********************
350 I must disagree with the analysis of the bandwidth required
351 for a particular baud rate. It was stated that theoretical limit
352 was hertz=baud/2.
353 I.E. 300 baud requires 150hz, or 600 baud requires 300 hz. However,
354 using ordinary 103 modems 600 baud can be transmitted, and the two
355 pairs of frequencies (1070/1270 and 2025/2225) are only 200 hertz
356 apart (not 300). While it is true that this is on the edge of
357 practicality, it is much less than the 300 hz that simple analysis
358 might imply is necessary. Certainly baud=hertz is wrong.
359 It is important to remember (as is often not recognized) that
360 bandwidth is not the same as maximum frequency response. That is,
361 a filter which passes everything from 1.00 Mhz to 1.1 mhz has a
362 bandwidth of 100 khz.
363 As I recall, I have seen modems advertised that put at least
364 4800 baud down an ordinary, switched line. However, at upwards of
365 $10k bucks, they were not cheap. In some cases, they could even
366 do 9600 baud. As phone signals are filtered to remove everything
367 above about 3000 hz, clearly the equation baud=hertz*2 is not
368 the real limit.
369 Let's not worry about such high speeds. Long before a 9600
370 baud modem becomes a $99.95 item, the phone Co. will be able to
371 give us 56k baud directly. Why should we take digital data, spend
372 huge amounts of money to turn it into analog signals, while the
373 phone co. spends huge amounts of money to turn analog signals
374 into digital and back again?
375
376 **********************
377 I notice a belief being presented here that the data transfer rate
378 is related to the baud rate. This is not true. A baud is simply the
379 smallest piece that the transmission medium can be divided into. It
380 does not mean that this has any relation to the data that is being
381 sent however. The data transfer rate is expressed as 'Bits Per Second'
382 or BPS. Any number of bits can be encoded in one baud (assuming
383 the data link itself is good enough to allow it thru).
384 I know of a 9600 BPS modem that transmitted 8 bits per baud using
385 a phase shift technic. Another way that data can be encoded on the
386 baud is by level shifting, however since there is some interaction
387 with the phase shifting, this method does not work as well together ]
388 with extensive phase shifting. The most common encoding methods used
389 for the various speeds is dibit (two bits per baud) for 2400 BPS useing
390 phase shift only. (The 212A modem uses this method as well).
391 At 4800 BPS they go to tribit encoding. This is normally split up into
392 2 bits phase shift, and 1 bit level shifting, but some do put all 3
393 bits into phase shifting.
394 FInally the 9600 BPS modems use two bits with phase shift, and two bits
395 with level shift. Alternatly they also use tribit phase shifting and one
396 bit level shift. Then of course there are the strange ones like the 8 bit
397 phase shifter that was mentioned previously.
398 ***** CISTOP MIKEY EXPLODING ANOTHER MYTH **** 24 APR 83 ******************
399 HI MICKEY-PLEASE CALL RICK CONCERNING BOARD INFO ANY TIME
400 HI MICKEY-THE LAST PART OF THE MESSAGE GOT LOST SOME WHERE-I'LL BE HOME
401 AFTER 4:00 SO GIVE ME A RING.THANK YOU***************4/24/83**************
402 That 1200/75 baud system sounds interesting. I have long wondered
403 why my UART would support transmitting at one baud rate while
404 receiving at another rate. This is the first I've heard of
405 equipment that would allow use of this feature. As for the
406 bandwidth arguments, I've seen explanations (which I don't
407 claim to understand) of why FSK is preffered over AFSK for RTTY
408 which show that the required bandwidth for the signal depends
409 not only on which frequencies are used for mark & space but on
410 how you switch from one to the other!
411 On a different subject I need some info on TRS-80 model
412 1 expansion interfaces. Does anyone know which of them WILL
413 support dual cassettes? Or does anyone know where I can get a
414 diagram of the cassette switching circuitry in the E/I?
415 ______________________________Leonard__________________________
416 The 1200/75 baud modem is just a respecified 202 type modem.
417 Ma bells 202 modem can do the same thing with a minor modification.
418 the main problem with it is that it reduces the maximum allowable
419 transmission rate to 1200 (a 202 can transmitt up to 1800 baud
420 over the phone lines.). But since most people only run the 202
421 at 1200 baud, this is not really a problem. For those of you who
422 will now probably ask, no the PCS-103 modem cannot provide the
423 75 baud back chanel. Even a 202 type modem needs the 'reverse' or
424 'back' channel installed and properly modified to do this. (It
425 is also sometimes called a supervisory channel.)
426 About FSK verses AFSK. First, many out there are probably asking
427 "What the heck are they?", Well, FSK stands for frequency shift
428 keying. This means that the transmitted frequency (That wistle you
429 hear coming out of your modem is shifted in frequency to transmit
430 data 1070Hz for a '0' and 1270 Hz for a '1'. AFSK means that instead
431 of shifting the base frequency (the carrier) the 1070Hz/1270Hz signal
432 is impressed upon the carrier frequency as a audio tone the same way
433 the music that comes out of your radio is tranmitted by modulating
434 a transmitted carrier. The reason the FSK method was used of RRTY
435 (radio teletype) has nothing to do with all the garbage that people
436 feed you about bandwidth and such, it has a much nore base reason.
437 When the RTTY was first introduced, there was no such thing as modems
438 as such the radio engineers had to figure out their own way of sending the
439 data. Since there was no advanced technology around, they did things the
440 easiest way they could. They started with the transmitter. The easiest
441 way to modulate a transmitter is to turn it on and off (called CW tranmission)
442 this is limitted as to how fast you can transmitt however, so they needed
443 to figure a better way to tranmit. The next easiest way is to change the
444 frequency of the transmitter. This can be done by throwing some additional
445 capacitance across the transmitters oscilator. This is quite easy to do
446 with a relay contact now since the old teletype equipment used relays
447 to do the transmission of their data, it not hard to see why they chose
448 this method of transmission. If they were to send it as AFSK they would
449 have to add an additional oscilator to send the data with.
450 In the reciever, the same kind of decoder is needed to convert the
451 data back to binary from the transmitted tones whether they used FSK
452 or AFSK. So the method used is based simply on the easiest way to
453 transmit the data. While it is true that FSK has a smaller bandwidth
454 over AFSK, don't believe all that garbage about that being the reason
455 for using it. In fact you will find a rapidly increasing use of AFSK
456 transmission occuring over the radio waves in the future. The reason
457 is again quite simple, it has nothing to do with engineering, it is
458 instead a matter of money and the understanding of the equipment
459 involved. Since there are an enormous number of computer modems out
460 there, they can be had for cheap and they are very reliable. To some
461 poor sucker out there who bearly knows how to turn the dial on his
462 radio this is very important. He dosen't give a hoot about bandwidth
463 and junk like that, all he wants is something that works. Since the
464 computers are already setup to run with modems, all that needs to be
465 done is to run the line to the radio instead of the phone line, and
466 your computer can now send data via your radio. There is one minor
467 problem here, and that is that most radio systems are setup to be
468 half duplex (one way at a time transmissions) while most computers
469 operate with full duplex (simultanious two way transmissions).
470 This is solved by useing the more expensive (and difficult) full
471 duplex radio circiuts, or to change the computer transmission to
472 half duplex which is also more difficult to do.
473 I do have a program which is nearly complete which will allow any
474 CPM based computer to send and receive data in half duplex mode.
475 I will let you know here when it is ready for release.
476 ***** CISTOP MIKEY RAMBLIN' ON AGAIN ***** 24 APR 83 *************
477 P.S. In my next rant I will discusse how you can transmit data over a
478 modem that was only designed to send data at 300 baud, yet send it at
479 600 baud. (Hint, it really is maxed out to only 300 baud when runing
480 true full duplex. ***** CISTOP MIKEY AGAIN ***************************
481 ----------------------------------------------
482 COULD SOMEONE LEAVE A LIST OF PHONE #'S FOR ALL THE BBS'S
483 IN THE METRO AREA....
484
485
486 LARRY 'SYRINX' GRAY
487
488 ===================================================
489
490 Consider the 'lowly' 6860 modem chip from Motorola. Specifically its
491 transmit section. In it, bits are converted to tones using a simple
492 3-bit D-A converter that is driven by a crystal-controlled counter.
493 What's so great about that? Well, two things. First, the tones are
494 guaranteed to be within about 0.1% of correct. Second, bit transitions
495 are PHASE SYNCHRONOUS. What does this mean? Instead of having two
496 separate oscillators at 1070 and 1270 and gating the appropriate one
497 onto the output when desired, there is one 'digital' oscillator
498 whose speed increases or decreases depending on which frequency is
499 desired. No sudden spikes on the output, etc.
500 Just recently, TI was severely criticized for producing a new
501 modem chip that WASN'T phase synchronous. Not everyone learns at the
502 same rate, apparently.
503 So if you want to run 600 baud on 103 protocol: Get two
504 direct-connect modems which are phase synchronous, have GOOD input
505 and output filters. What else? Stay away from GTE.
506 *******************************************************************
540 CBBS 284 xxxx
543 RCPM2 641-xxxx
546 CONN 80 281-xxxx although it hasn't been up for a year!
548 BIT BUCKET 761-xxxx
549 The so called baud rate is accurately the rate of change of the signal,
550 but is often used to mean the data rate. Sorry, I goofed and used it this
551 way. So: the DATA RATE can be up to the twice the bandwidth for binary
552 data means the same thing as the BAUD RATE can be up to 1/2 the bandwidth
553 The shift frequency used to send data is not the bandwidth, it is only
554 meaningful at loww data rates anyway, where it is the minimum bandwidth.
555 In theory, any method of modulation will work, but inpractice only
556 certain ones are used, because they match the medium. The use of AFSK,
557 for instance, looks easy, but if you are thinking AFSK on and AM or FM
558 radio, forget it. However, when placed on a good single sideband it is
559 able to create the same signal as true RF FSK, and is commonly so used.
560 The use of 103 modems at higher than 300 baud is not so unusual, but
561 is out of spec because the standard spec was designed for reliable
562 transmission over standard (ie poor) phone lines. The high limit is the
563 fact that we expect 2 way communication, and the signal you are sending
564 out can be as much as 1000 times as powerful as the receive channel.
565 It is necessary to filter out the send signals, as well as all other
566 noise on the line, and at extemely high data rates the send and receive
567 bands overlap. In fact often less expensive modems are easier to push
568 to high speed, because their cheaper filters are wider band.
569 More theory on bandwidth: simple anplitude modulation, AM, has a
570 bandwidth twice as wide as the modulating signal, but filtering off
571 one sideband gives SSB, with 1 to 1 bandwidth. Simple fequency mod gives
572 a signal with an endless group of sidebands spaced at the modulating
573 frequncy, and phase mod does the same; but simple filters can cut off
574 all but a few, and still get good results. Frequency shift keying is
575 a type of FM, but the modulating signal is here a square wave. For data
576 all we need is enpugh fidelity to figure out what was sent, so we can
577 filter a lot harder, but that bottom sideband must be there. The carrier
578 isn't needed if we know what it was.
579 The actual bandwidth needed is mostly determined by how many of the
580 sidebands we need to reconstruct the original signal, and this depends
581 mostly on how elaborate our equiptment is, and how many errors we can
582 accept. (As well as the final determination, the phone line.)
583 The CBBS for some time used a modified 103 that would accept 450 or 600
584 baud, but this wasn't apparently widely used because of compatability
585 problems. Their being in GTE are may have had something to do with my
586 mever being able to talk at over 300 baud.
587 I beleive, however, that we would do better to use 202 type modems and
588 smarter terminals to handle the turn around: this gives us 1200 or so
589 and some semblance of two way transmission; or at least this is the
590 best we can do until 212 becomes cheap enough to use. (Which will happen
591 as soon as the industrial customers need faster data, and the 212
592 becomes as obsolete as the 103 is now.)
593 vv^v^v^v^v^v^v^v^v^v^v^v^v^v^v^B.A.D.v^v^v^v^v^v^v^v^v^
594 ........................................................
595
596 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
597
598 FOR SALE:
599
600 APPLE II 48K
601 BLACK -N- WHITE TV (12")
602 TAPE RECORDER
603 OVER 100 BLANK TAPES
604 WITH 30 TAPES FULL OF MISC SOFTWARE.
605 MISC MANUALS
606 PADDLES
607 PROGRAMMERS AID #1 (ROM)
608 UPGRADE TO II PLUS $100 MORE
609
610 SYSTEM FOR $1000 WITH OUT UPGRADE
611 $1100 WITH
612
613 CALL 657-xxxx
614 AFTER 3:00
615 ASK FOR LARRY.
616
617
618 **************************************************************
619
620 P.S. OR LEAVE MESSAGE ON BIT BUCKET OR BACKWATER .......
621 ***************************************************************
622
623 ------------
624 As for cheapness, 212 modems are getting better. At about $350 or so
625 for a bargain-basement one, it is not out of the range of many people.
626 Of course, there's the chicken-and-egg problem, which is being solved
627 now that CBBS, etc, are going with it. If people get into the habit
628 of calling bbs's long distance and want to avoid astronomical phone
629 bills, they'll go to 1200. I guess we have run out of room.........