rees@dabo.ifs.umich.edu (Jim Rees) (04/10/90)
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]ted@mbunix.mitre.org (Ted Ede) (04/12/90)
I'd be interested in knowing more. I've tried to get the info from
the supplier of the phone (Novatel, what a surprise.) and they won't
give it out easily.
Ted Ede -- ted@mbunix.mitre.org -- The MITRE Corporation -- Burlington Road
linus!mbunix!ted -- Bedford MA, 01730 -- Mail Stop B090 -- (617) 271-7465
cjp%megatek.UUCP@ucsd.edu (ChristopherDude Pikus) (04/12/90)
From article <6236@accuvax.nwu.edu>, by rees@dabo.ifs.umich.edu (Jim Rees): > Does anyone have the new Motorola super-small $1400 shirt-pocket > cellphone? Any opinions? Does it work and do you like it? My boss had one and I spent a few days using it. It is as small as they say, but has limited battery life. In the demo model the battery is only 1/4" thick. With it you only get 15 min. talk time. They have an optional battery (1" thick, 18 oz.) that provides the standard 12 hr. standby, 70 min. talk time. If you use the optional battery it is no longer really a shirt pocket phone. With the small battery, it is about 7/8" thick and weighs 13 oz. Another complaint (which is for most handheld phones anyway) is that the small antenna limits performance. The Motorola phone compared unfavorably with other handhelds that I have used. Packaging options severly limit design choices. > 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? In a previous life I worked for a company that wanted to put a cellular phone into a laptop computer. As such our group ended up dissasembling several cellphones (including the Motorola above) to see what was involved. They all use duplexors. The bandwidth of both the transmit and receive parts is 25 mHz each. Transmit is 836.5 Mhz +/- 12.5 Mhz, receive is 881.5 mHz +/- 12.5mHz. Murata actually makes these parts with these specs. (3, 4, or 5 pole filters). The Motorola cellphone is just standard technology with much emphasis on packaging technology man miniturization. It has a duplexor that measures 1/4x3/4x2". And the Moderator noted, regards programing of phones by end-users: > 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] I feel that the carrier that is providing the service should be the one programming the phone to make sure that it is not ac- cidentally (or fraudulently) programmed wrong. Since you will be daling with the carrier when contracting for service, why not have them program it. Regards, Christopher J. Pikus, Esquire Megatek Corp. INTERNET: cjp@megatek.uucp San Diego, CA UUCP: ...!{uunet hplabs!hp-sdd ames!scubed ucbvax!ucsd}!megatek!cjp