From: Brian Kantor <brian@ucsd.edu>
Subject: Re: Cellular Phone Antenna Question
Date: 17 Oct 89 20:35:54 GMT
Reply-To: Brian Kantor <brian@ucsd.edu>
Organization: UCSD Network Operations

In article <telecom-v09i0456m04@vector.dallas.tx.us> folta@tove.umd.edu.UUCP 
(Wayne Folta) writes:
>X-TELECOM-Digest: volume 9, issue 456, message 4 of 7

>Can anyone tell me about cellular phone antennas?  Why the little
>curly part of the antenna (does it have something to do with
>horizontal v. vertical polarization?)? 

A non-technical explanation:

The cellular antenna is really two vertically-polarized antennas of
approximately 1/2 wavelength, and the curly part can be viewed as a
delay line to cause the two sections to work in phase.  Thus the
antenna has an effective "gain" (i.e., works better) than a simple
antenna.

I have a similar antenna for my ham radio equipment, except that as
it's for a frequency that is about half that of the cell-phone band,
my antenna is about twice the size.
	
          - Brian

From: Brian Kantor <brian@ucsd.edu>
Subject: Re: Cellular Phone Antenna Question
Date: 23 Oct 89 04:00:59 GMT
Reply-To: Brian Kantor <brian@ucsd.edu>
Organization: The Avant-Garde of the Now, Ltd.

In article <telecom-v09i0468m05@vector.dallas.tx.us> Kent Borg <lloyd!kent@
husc6.harvard.edu> writes:

>I always thought the main reason the center loading coil was there to
>let everybody know that you have a cellular telephone, i.e., that it
>was put there for marketing reasons, to give cellular telephones an
>identity and to look cool.  How much gain is it really worth?

Roughly 6dB (~4x signal strength, or given all else equal, about twice
the range) over an equivalent 1/4-wavelength stub, which would be
about 3 inches long.  You can use the little 3-inch whip if you don't
mind the reduced range.  There is another factor: the radiation angle
of the curly-whip antenna is lower and tends to hit the cell-sites
better, whereas the 1/4wave has a real high radiation angle and the
signal tends to shoot off into space.  If you happen to live in an
area where the cell sites all are on top of good tall mountains (like
the 6,000 ft ones around San Diego and Los Angeles), the 1/4wave
antenna will actually work better close in to the foothills.

>One good reason for getting rid of the open coil would be so bits of
>outdoors don't get stuck in there, changing the inductance of the
>coil, and screwing up the performance of the antenna.

Older design antennas had the coil encapsulated in a plastic tube,
which broke every time it went through the car wash, and had much more
wind resistance so that the antenna bent away from the vertical at
highway speeds.  Lack of verticality is a SERIOUS range killer; if the
antenna were to fall over horizontal, you'd face a theoretical 20dB
loss in signal strength.

>Another reason would be so that people won't know you have a cellular
>telephone.  This might not be a good thing.  How easy is it to change
>the serial number on these puppies?  They certainly would have very
>little fence value if it were impossible to make calls because the
>radio identifies itself and has been reported stolen.  Maybe they
>don't get stolen much...  Anybody know?

They get stolen a lot.  You can buy a disguise whip which doesn't look
much like anything, but it's got poorer range.  Hide the handset,
since it's the glittering attractive thing.  And you might want to
drill a hole in the center of your car roof and put in a real antenna
instead of the glass-mount type.  Not only will it look less like a
typical cellphone install, but it'll also have better range.

Changing the serial number of a stolen cellphone theoretically
shouldn't be terribly hard, since it's just burned into a ROM chip,
but I'm told that they stopped putting the ROM in a socket and started
covering the soldered-in chip with epoxy to make it much much harder
to do.  My friend at a local two-way shop says they have to exchange
the main circuit board on the rare occasion when the ROM goes bad,
since there's no way to get the chip loose without destroying the
board.  Apparently that didn't used to be the case.

	- Brian