[GreenKeys] Early Mobile Telephone equipment

[Peter Gottlieb]

I do remember a bunch about the IMTS system.  I was sent to a course on 
setting up one of the latter Motorola IMTS base stations then supervised 
and signed off on one such install.  I also had a UHF units in my car, 
it was the really big and heavy one which used a varactor tripler to get 
into the 450 MHz area.  The PAs were somewhat unreliable.  The 
supervisory board was a mass of discrete components and always fun to 
work on.  These units used channel elements (crystals mounted in their 
own cans with oscillators).  Later on Motorola came out with the 
synthesized Pulsar mobiles which were much better.

There were two sets of channels for each city in both VHF and UHF.  One 
set was for the monopoly carrier (eg, Bell System) and the other set for 
the new independent carrier.  There were very few channels as you note 
and there was a significant waiting list to get a phone.  If I remember 
correctly, it was 6 years in the NYC area.  The IMTS was a dialtone 
system; when you went off-hook your phone had an interaction with the 
base system where your phone number was sent in and then you got a 
dialtone.  Dialing was rotary and tone encoded with parity tones.  When 
that CO in NYC burned down the Bell System "commandeered" the IMTS 
systems and used them for emergency communications with cars driving 
around making important calls for people until basic phone service was 
restored.

The phones had only 7 digits of phone number setting.  In the Bell 
system, the phone number (which was set with jumpers in the phone) was 3 
digits for the area code then the last four digits of your mobile 
number.  Independents did whatever they wanted, some followed this, 
others didn't.

I had a big fat HT-220 which had a bunch of the IMTS channels crystalled 
and I could talk to the operator and get her to connect me if I said 
some magic words.  This had been loaned to me from one of my clients and 
they refused to take it back later.  I think I gave it away when the 
battery would no longer hold a charge.

When I bought my first cellular phone Motorola had a deal where you 
would get a $500 credit if you turned in your old phone and believe it 
or not they took my ancient IMTS unit and I did get that check from 
them.  I still see the mobile units and control heads at hamfests.

Word from an insider at Motorola was that the first cellular trial in 
NYC was faked.  There was a tech pulling the levers behind the curtain, 
the automatic part was not yet ready.  Nevertheless, the technology 
behind the idea was sound and developed into the revolution that cell 
phones became.

Peter




Duncan M. Brown wrote:
> Anyone with early mobile telephone equipment that you don't know what to do
> with, the Antique Wireless Assoc. Museum would appreciate having it.  I
> have put together a small display of IMTS & early cellular equipment for
> the Museum, but we do not have anything prior to IMTS.
>
>
> A little more history:
>
> The first Bell System Mobile Telephone service began in St. Louis 17 June
> 1946 on on six channels (120 Kc spacing) in the 152/158 Mc band.  These
> channels were later split into 60 Kc and then 30Kc channel spacings and
> were given two-letter desiginations starting with "J" or "Y": JL, YL, JP,
> etc. (were one of these letter groups the earlier pre-split channels?). 
> There were plans to split the channels again into 15 Kc channels with "X"
> designators: eg XJ, XK, etc.  This was never instituted in the US as the
> Cellular channels were finally opened. (But they were in use in Canada in
> 1985.)
>
> The Mobile Telephone Highway service started in 1947 in the Boston to New
> York City corridor on 35/44 Mc. and used "Z" designators: ZO, ZF, ZH, etc.
> As of 1985, there were still two dozen cities in the US using the Z
> channels. These channels were shut down in about 1988.
>
> In 1956, 12 UHF channels with 25 Kc spacing were made available in the
> 454/459 Mc band and had channel designators starting with "Q": eg QC, QJ,
> QD, etc.
>
> In 1953, AT&T proposed to the FCC a "broadband" mobile telephone system
> operating in the 800Mc region. But it took until 1978 for the first
> cellular test system to go on the air and not until 1983 for the first
> commercial cellular system to go on the air (in Chicago).
>
> IMTS started in 1964 with field trials in Harrisburg, PA.  It was initally
> known as "Interim Mobile Telephone Service" ("interim" until cellular was
> available).  When they realized that cellular was a ways off, it was
> changed to "Improved".
>
>
> Duncan Brown, K2OEQ
>
> AWA Electronic Communication Museum
> http://www.antiquewireless.org
>
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