Eric, I think the reason antenna manufactures use dbi over dbd is dbi is higher...the higher the spec the more impressed is the customer. Most Hams probably do not know how to read the spec reference, dbi or dbd. They see db.
When a Ringo-Ranger is advertised in Ham magazines it has 6 db gain. When advertised in commerical publications/catalogs it has 4.5 db gain...same antenna, same part number. I think those working with commerical and other professional systems know the specs and look for details. When they see db they want to know dbi or dbd and maybe how determined...prove your spec. Could never understand why a Diamond long 18 ft dual band antenna has about 8 dbd on VHF/11 dbd on UHF when a commerical antenna like the Super Station Master or DB224 has 6 db. Think the commerical people know why, not, hi. QST for a long time refused to print gain specs in the ads for they knew most was smoke. 73, ron, n9ee/r --- In Repeater-Builder@yahoogroups.com, "Eric Lemmon" <[EMAIL PROTECTED]> wrote: > > The Telecommunications Industry Association, an international organization > which develops standards to which nearly all countries of the world have > subscribed, has already taken steps to correct the misleading practice of > indiscriminately using dBi where dBd is appropriate. > > According to TIA-329-C, published in 2003, base station antenna gain for > less than 1 GHz shall expressed in dBd using a dipole antenna as a > reference. Antenna gain for 1 GHz and above shall be expressed in dBi using > a theoretical isotropic radiator as a reference. There are no exceptions. > So, why are some manufacturers still using dBi for their 2m and 70cm > antennas? There are probably several answers to that question, such as: > > 1. Perhaps most antenna buyers don't know the difference between dBi and > dBd. > 2. Perhaps most antenna buyers believe whatever the ad copy says. > 3. Perhaps the company owner is an old-school believer that dBi is the only > "true" gain unit. > 4. Perhaps the antenna designer knows about TIA-329-C, but chooses to > ignore it. > > It should be obvious that microwaves, which begin around 1 GHz, behave a lot > like light and can be focused with a parabolic reflector. Short radio waves > are easy to visualize as being generated by a point source, very much like a > bulb in a parabolic flashlight reflector. Such point sources can be easily > expressed as isotropic radiators, and the leap to dBi is logical. The > wavelength of lower-frequency waves in the VHF and UHF spectra are not point > sources, and it is illogical to expend any effort "converting" from one > reference to the other. As several others have pointed out, there is about > 2.14 dB difference between the absolute gain expressed as dBi and that > expressed as dBd. > > Unfortunately, there will always be some "fringe group" that will argue > until the end of time that dBi is the Nirvana of antenna gain expression. I > doubt that the decision by the TIA to limit dBi as an antenna gain unit to 1 > GHz and above will change their beliefs. Getting the antenna manufacturers > to properly report the gain of their products is quite another thing. As > previous posters have mentioned, some popular antennas are junk that has > never been properly tested on an antenna range, resulting in ridiculously > inflated and undocumented claims of performance. If clueless buyers believe > the hype, nothing is likely to change. That's a shame- but hey, it's the > American Way! > > 73, Eric Lemmon WB6FLY >
