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Telephone History
Mobile Telephone History ---- Pages: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (Packet switching) (Next topic: Standards)

WhatWhat was used before cell phones

IMTS photo

Livermore Data System model LAP-2000, circa 1982. Self contained mobile telephony before cellular. Unit weighs 18 pounds, has only 11 channels, puts out 30 watts, and measures battery life in minutes. Today's handheld mobiles weigh ounces, can work a thousand frequencies, use less than a watt to reach the base station, and can go for days on a charge. Few cities had 11 channels operating, most small cities just one, San Francisco four, Los Angeles thirteen. Long waits to make calls were common yet demand so great that multi-year waiting lists existed in every major city. Although IMTS equipment is still used for other things, it is my understanding that in America IMTS service is now defunct.

 


Livermore LAP-2000 Control Panel Description and IMTS frequency assignments
  Channel Designation Base Station Frequency  Mobile Telephone Frequency
       
  YS 152.72 157.98
  YR 152.75 158.01
  YP 152.60 157.86
  YL 152.54 157.80
  YK 152.66 157.92
  YJ 152.63 157.89
  JS 152.69 157.95
  JR 152.81 158.07
  JP 152.57 157.83
  JL 152.51 157.77
  JK 152.78 158.05
 

In Improved Mobile Telephone Service calls were placed automatically, without having to go through a mobile operator. Base station and mobile were on different frequencies; one could have a normal, back and forth telephone conversation without having to wait for the other party to stop talking. Although the earlier MTS system used different frequencies as above, echo problems allowed only one party to talk at once. IMTS developed echo canceling routines which finally allowed full duplex operation. Still, provision was made for more primitive systems, hence the pushbuttons one could manually depress to select a channel. And a PTT or push to talk select button, to converse on systems that did not have full duplex communications.


More info on the briefcase model! --->

Here are the MTS and IMTS Frequencies:
 
VHF Low Band
Channel Base Frequency Mobile Frequency
ZO 35.26 43.26
ZF 35.30 43.30
ZH 35.34 43.34
ZA 35.42 43.32
ZY 34.46 43.46
ZC 35.50 43.50
ZB 35.54 43.54
ZW 35.62 43.62
ZL 35.66 43.66

VHF High Band
Channel Base Frequency Mobile Frequency
JL 152.51 157.77
YL 152.54 157.80
JP 152.57 157.83
YP 152.60 157.86
YJ 152.63 157.89
YK 152.66 157.92
JS 152.69 157.95
YS 152.72 157.98
YA 152.75 158.01
JK 152.78 158.04
JA 152.81 158.07

UHF Band
Channel Base Frequency Mobile Frequency
QC 454.375 459.375
QJ 454.40 459.40
QO 454.425 459.425
QA 454.45 459.45
QE 454.475 459.475
QP 454.50 459.50
QK 454.525 459.525
QB 454.55 459.55
QO 454.575 459.575
QA 454.60 459.60
QY 454.625 459.625
QF 454.650 459.650

Resources

MOTOROLA EARLY LAND MOBILE EQUIPMENT INDEX, 1938-1946

http://www.mbay.net/~wb6nvh/Motadata.htm (external link)

Geoff is an ardent mobile radio enthusiast, please visit his site soon.

More IMTS madness? Of course. Take a look at a company newsletter describing the 1982 cutover in Pac Bell land:
 
Page One/ Page Two/ Page Three/ Page Four

(1) Service cost and per-minute charges table/ (2) Product literature photos/ (3) Briefcase Model Phone / (4) More info on the briefcase model/ (5) MTS and IMTS history/ (6) Bell System (7) Outline of IMTS/ (8) Land Mobile Page 1 (375K)/ (9) Land Mobile Page Two (375K)/ (10) The Canyon GCS Briefcase Telephone

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