folta@tove.umd.edu (Wayne Folta) (10/17/89)
The price of cellular phones has been dropping recently, so I got a reconditioned phone for $230 (Fed. Expressed to my door). It comes in a backpack, with a magnetic-mount antenna. I'd like to put a little work into it and make a nicer, more permanent set-up, so: 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?)? Why is the Radio Shack window- mount antenna so much smaller than my magnetic mount? And why does the Radio Shack antenna have such a large passive coupler (I think) base? I would like to disguise the antenna, to avoid break-ins, as the rest of the system will be hidden. Any clever ideas here? Maybe use the FM antenna? Maybe an antenna in the back window? Wayne Folta (folta@tove.umd.edu 128.8.128.42)
brian@ucsd.edu (Brian Kantor) (10/18/89)
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
kent@husc6.harvard.edu (Kent Borg) (10/21/89)
In article <telecom-v09i0458m07@vector.dallas.tx.us> Brian Kantor <brian@ucsd. edu> writes: >X-TELECOM-Digest: volume 9, issue 458, message 7 of 10 >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?)? >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 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? 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. 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? Kent Borg "Then again I could be foolish kent@lloyd.uucp not to quit while I'm ahead..." or -from Evita (sung by Juan Peron) ...!husc6!lloyd!kent
john@zygot.ati.com (John Higdon) (10/23/89)
In article <telecom-v09i0468m05@vector.dallas.tx.us>, lloyd!sunfs3!kent@husc6. harvard.edu (Kent Borg) writes: > 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. > Another reason would be so that people won't know you have a cellular > telephone. This might not be a good thing. If you really don't want people to know you have a cellular phone, use a handheld. I had a standard cellular car phone for a couple of years. When it died, rather than pay a fortune to have it repaired I decided to move to a handheld. I never expected it to work very well in the car, particularly while in motion, and was certainly surprised to find that it worked better! There had obviously been some improvement in the transceiver technology in those intervening years. Needless to say, I find that my handheld is all I need for mobile communications and there is no unsightly antenna on my truck. Not really yuppie-approved, but such is life. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !
brian@ucsd.edu (Brian Kantor) (10/23/89)
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
hamilton%cell.mot.COM@uunet.uu.net (Danial Hamilton) (10/24/89)
> If you really don't want people to know you have a cellular phone, use > a handheld. I had a standard cellular car phone for a couple of years. > ... > ... Needless to say, I find that my > handheld is all I need for mobile communications and there is no > unsightly antenna on my truck. Not really yuppie-approved, but such is > life. I don't care who says it's safe, I just can't feel comfortable about radiating 800 MHZ RF energy 3-4 inches from my brain.
john@zygot.ati.com (John Higdon) (10/26/89)
In article <telecom-v09i0471m06@vector.dallas.tx.us>, motcid!hamilton%cell. mot.COM@uunet.uu.net (Danial Hamilton) writes: > [regarding handhelds] > I don't care who says it's safe, I just can't feel comfortable about > radiating 800 MHZ RF energy 3-4 inches from my brain. Those of us using handhelds and other cellular phones appreciate those who don't like using them for whatever reason. It means less traffic for the rest of us :-) Seriously, I can respect those who are cautious. What really gets to me is when our government decides that we must be protected from all manner of harmful influences and passes laws that prevent those who are willing to take the risks from doing so. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !