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From: rees@dabo.ifs.umich.edu (Jim Rees)
Newsgroups: comp.dcom.telecom
Subject: Cellular Tech Questions
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Date: 10 Apr 90 15:18:15 GMT
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Reply-To: rees@citi.umich.edu (Jim Rees)
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X-Telecom-Digest: Volume 10, Issue 245, Message 10 of 11


I enjoyed John Covert's rundown on cellular channel capacity.  A few
more questions/observations:

Does anyone have the new Motorola super-small $1400 shirt-pocket
cellphone?  Any opinions?  Does it work and do you like it?

I assume that any cellphone has to have an RF duplexor.  This is a
device that prevents the transmitted RF from overloading the receiver
front end, and lets you use the same antenna for transmit and receive.
These are usually mechanical cavity resonators.  At 900Mhz these would
be about 8cm tall.

But in a cellphone, they must use something more sophisticated,
because the transmitter and receiver both have to be frequency-agile.
And I don't see how they could fit a duplexor into those little $1400
Motorola jobs.  Any clues as to how these little guys work?

Regarding cellphone mecca, Hong Kong: You see people in the subway all
the time, impatiently jabbing at their phones, waiting for the
"service unavailable" light to go out, because the RF can't reach into
the tunnels.  I'm surprised the cell company hasn't put slotted coax
into the tunnels.  Also, from the top of Peal Rise, I would think you
could see/hear every cell in HK and Macau.  Do cellphones work up
there or is there too much adjacent cell interference?

                          -------------

[Moderator's Note: A reader has suggested a series of articles in the
Digest regarding how to program various models of cellular phones.
Included would be a discussion of security and supervisory techniques
used by the carriers to detect fraud. Both the reader and myself feel
that people who buy cell phones (like any other expensive electronic
equipment) are entitled to know how to program their phones and how
they operate. Both of us feel a cell phone user should not be at the
mercy of a salesman or dealer to handle the reprogramming in the event
a change of carrier is desired.  What do you think?    PT]