[BC] rotaries

[Gary Glaenzer]

From: "Tom" <Radiofreetom at gmail.com>

> Um...
>
> I know this was supposed to be all-in-fun, but I seem to recall that
> some of the later VHF mobile phones had a (rotary) dial.  Not sure WHY;
> perhaps channel select?

channel select was automatic in 'Home' mode, and manually in 'Roam' or 'manual'(basically
PTT on the channel)

the Motorola 'Pulsar' used touch tones as an option for dialing with the 'Pulsar II'
series of control heads

but right up thru the early 90's, most mobile phones used dials

why ?

because of the structure of the signalling...alternate bursts of two tones were used to
signal the base station as to what digits were being dialed, and that was easily
accomplished by letting the dial 'interrupter' generate the timing

from Wiki, take it for what it's worth.......

"The basic operation of IMTS was very advanced for its time, considering that integrated
circuits were not commonly available. The most common IMTS phone, the Motorola TLD-1100
series, used two circuit boards about 8 inches square, to perform the channel scanning and
digit decoding process, and all logic was performed with discrete transistors. In a given
city, one IMTS base station channel was "marked idle" by the transmission of a steady 2000
Hz "idle" tone. Mobiles would scan the available frequencies and lock on to the channel
transmitting the idle tone. When a call was placed to a mobile, the idle tone would change
to 1800 Hz "channel seize" tone, and the 7 digit mobile number (3 digits of area code and
4 digits of subscriber number) would be sent out as rotary dial pulses, switching between
2000 and 1800 Hz to represent digits. Any mobile recognizing that the call was for someone
else would resume scanning for mark idle tone, while the called mobile would then transmit
2150 Hz "guard" tone back to the base station. This would also initiate ringing at the
mobile, and when the mobile subscriber picked up the phone, 1633 Hz "connect" tone would
be sent back to the base station to indicate answer supervision and the voice path would
be cut through. When the mobile hung up, a burst of alternating 1336 "disconnect" and 1800
Hz "seize" tones would be sent to allow the base station to service another call."

the TLD-1100 was superceded by the 'Pulsar', using IC's rather than discrete transistor
circuits for counting pulses and generating tones

the IMTS system was limited to 10,000 numbers per area code, the number was your area code
+ XXXX

BUT........there were several restriction that limited 'real # of #s' to about 7700....no
leading zero's, no more than 2 digits the same in a given # are two that I recall