Path: utzoo!attcan!utgpu!watmath!iuvax!rutgers!texbell!vector!telecom-gateway From: brian@ucsd.edu (Brian Kantor) Newsgroups: comp.dcom.telecom Subject: Re: Cellular Phone Antenna Question Message-ID: Date: 23 Oct 89 04:00:59 GMT Sender: news@vector.Dallas.TX.US Reply-To: Brian Kantor Organization: The Avant-Garde of the Now, Ltd. Lines: 54 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 469, message 7 of 11 In article Kent Borg 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