Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: "Robert P. Warnock" Newsgroups: comp.dcom.telecom Subject: Re: First Time Cellular Phone Buyer Needs Advice Message-ID: <2439@accuvax.nwu.edu> Date: 28 Dec 89 04:52:50 GMT Sender: news@accuvax.nwu.edu Reply-To: rpw3%wpd@sgi.com Organization: Silicon Graphics Inc., Mountain View, CA Lines: 42 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 9, Issue 598, message 2 of 9 In article <2382@accuvax.nwu.edu> John Higdon writes: +--------------- | Antenna "gain" is most common in the RF world. It involves the amount | of energy radiated in a given direction from the antenna. In a given | azimuth, a 5/8 wave antenna (as used in cellular mobile phones) | radiates more energy than a 1/2 wave reference dipole for a given RF | input... +--------------- [...and more good tutorial stuff about Effective Radiated Power (ERP) and how you get effective gain...] Except that I thought the "reference" for ERP was the hypothetical isotropic radiator, not a dipole. An isotropic radiator's pattern *is* a uniform sphere; a 1/2-wave dipole is more like a doughnut with a really small hole in it. (The dipole "threads" the hole. That is, the maximum power from a dipole is broadside to the antenna.) A 1/2-wave dipole has (I think) about a 3dB gain (factor of 2 power gain), due to the fact that it doesn't "waste power" radiating off the ends. Even a 1/4-wave whip has some gain (as long as you hold it "up" and don't actually point it at the cellular site!). A properly phased stacked array of a ground plane plus 1/4-wave plus 1/2-wave (which is what I think you're calling a 5/8-wave, which is *about* what it is after the account for the shortening due to the loading-coil effect of the phasing coil between the two sections) has an (advertised) gain of about 5dB, or a power gain of 3.2 or so. This is how Radio Shack et al. get away with calling a 1/2-wave whip (the funny thing which is really *center*-fed 'cause the bottom half is the folded-back shield of the feed line) a "3dB gain" antenna, even though ita gain is barely a dB or so more than a 1/4-wave whip. It's 3dB with respect to an *isotropic* antenna. Rob Warnock, MS-9U/510 rpw3@wpd.sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311