Which begs the question: Why are antenna manufacturers and vendors still using dBi to express gain for antennas operating at VHF? The term dBi represents gain of an isotropic (point-source) radiator such as an antenna with a parabolic reflector; it is inappropriate to use dBi for a dipole radiator. I think we all know the answer- it "sounds better!"
The international communications engineering organizations have decreed that dBd shall be used for antennas below 1 GHz, and dBi shall be used for antennas 1 GHz and above. Here's some statements from TIA-329-C, entitled "Minimum Standards for Communications Antennas, Base Station Antennas" published by the Telecommunications Industry Association and the Electronic Industries Alliance, in harmony with other international standards: "3.2.1 Standard Gain Unit Below 1 GHz. The gain of a theoretical (lossless) half-wave dipole shall be used as the standard gain unit. The gain of the standard gain antenna in the plane perpendicular to its axis is therefore zero dBd. The gain of an antenna shall be expressed in dB over that of a theoretical (lossless) half-wave dipole in dBd." "3.3.1 Standard Gain Unit 1 GHz and Above. The gain of a theoretical isotropic point source shall be used as the standard gain unit. The isotropic point source radiates uniformly in all directions; therefore the gain of the isotropic point source shall be zero dBi. The gain of an antenna shall be expressed as that over a theoretical isotropic source in dBi." The TIA-329-C document was published in August 2003. I find it interesting that many antenna manufacturers claim to build their products in accordance with TIA and EIA standards, but ignore this significant document. If you wish to purchase a copy of TIA-329-C, go here: http://tinyurl.com/58hjvo 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Saturday, May 10, 2008 9:00 AM To: [email protected] Subject: RE: [Repeater-Builder] Re: antenna question - Dip It and Scotch Kote and Kry At 5/10/2008 04:36, you wrote: >Paul, > >This length always leads me to telling Hams that the 17 ft Comet does not >have the 8+ dbd gain the package says. I don't recall the package saying dBd, but their website clearly indicates 8.5 dBi @ 146 MHz. BTW, I measured the gain of the GP9 @ 440 MHz (compared against a known Yagi antenna using multiple far-field signal sources). It is in fact as they claim, around 11.5 dBi. Bob NO6B
