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91439306
15,000 Watts of Bass Power
join:2002-10-16
New Milford, CT
| reply to DaDogs
Re: Actually
said by DaDogs  :said by Matt :IFF you get a 9 dBi omni directional antenna and attach it to a 27 dBm radiator (.5) watts. You can legally radiate at 36 dB EIR four (4) watts. There is no such thing as a "9 dBi omnidirectional antenna" by the very definition. Omnidirectional IS an isotropic radiator, which, by definition is 0dBi. The means of increasing gain is by restricting radiation to a particular plane or direction. Thus the term, dBi, being the gain of the subject antenna, referenced to an isotropic (omnidirectional) radiator. Other references can be dBd (referenced to a halfwave dipole antenna, which has 3dBi gain (referenced to an isotropic radiator. Thus, isotropic have no gain, or unity gain, because they radiate in all directions. In practice, there is no man made perfect isotropic radiator because of nearby influences distorting the pattern to make it somewhat directional. So we talk about antenna gain being referenced to something, either the dipole or the hypothetical isotropic radiator. Gain is achieved by focusing the energy in a particular plane or direction, thus an omnidirectional can, by definition, have no gain. --
Take care,
Mark & Mary Ann Weiss
Hear my Kurzweil Creations at: »www.dv-clips.com/theater.htm
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
1 edit | said by 91439306 :said by DaDogs :IFF you get a 9 dBi omni directional antenna and attach it to a 27 dBm radiator (.5) watts. You can legally radiate at 36 dB EIR four (4) watts. There is no such thing as a "9 dBi omnidirectional antenna" by the very definition. Omnidirectional IS an isotropic radiator, which, by definition is 0dBi. The "popular" usage of the term "omni-directional antenna" is an antenna which has uniform gain in the plane of the earth for 360 degrees around.
You may want to delude yourself into believing that is not what people understand it to mean but I will refer you to the vast compendium of literature upon the subject. Including the very FCC document we are referencing.
said by 91439306 :The means of increasing gain is by restricting radiation to a particular plane or direction. Thus the term, dBi, being the gain of the subject antenna, referenced to an isotropic (omnidirectional) radiator. Perhaps we should correct the reference above so that it agrees with the FCC's use of the term in their documents as well as the use of the term in the community. Google for "omnidirectional antenna" and show me the Isotropic radiator you find which is equated to the omnidirectional antennas you find for sale...
This is crap. We don't need to redefine the language of the industry... Gawd...
said by 91439306 :Other references can be dBd (referenced to a halfwave dipole antenna, which has 3dBi gain (referenced to an isotropic radiator. I'm sorry, but that is incorrect. In the industry we currently consider a dipole to have approximately 2.17 dBi gain. My computer models of dipoles generally show about that much gain, by the way.
said by 91439306 :Thus, isotropic have no gain, or unity gain, because they radiate in all directions. Yes, but omnidirectional antennas, as the term is used in the wireless industry, and by the FCC in its literature, may indeed exhibit gain over an isotropic radiator.
...
Thanks for the basics on antennas. May I refer you to one of my web sites.
»www.freeantennas.com
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91439306
15,000 Watts of Bass Power
join:2002-10-16
New Milford, CT
| Popular in what era? Back in the 50s and 60s (and even into the 70s) when I designed antennas for VHF broadcast applications, the common term for omnidirectional was 'isotropic radiator'. The closest antenna to being an isotropic radiator in today's market are the ERI 'rototiller' circularly-polarized FM broadcast antennas so commonly in use. It isn't until you stack them and control the phase of the input power to each bay that directional patterns along the horizon come into play. There are quite a few FMs in the class A FCC designation that are close to isotropic in radiation pattern and are termed 'omnidirectional'.
Now it is true that you can have a series of dipoles stacked vertically to provide a doughnut-shaped pattern, and by increading the number of vertical radiators, one can compress the vertical plane of radiation to increase reach along the horizon.
Which FCC document are you referencing that talks about the 9dBi radiator? It seems that many in the FCC in recent years have lost touch with the proper definitions for technical terms, and I have noticed a propensity toward these mistakes since 1996 or so.
It seems the industry has redefined the language of science and engineering. Most likely the marketing branches of various manufacturers.
Your model of the 2.17dBi dipole may take into account certain factors like conductivity of ground, capacitive coupling and other real world factors that affect actual gain, vs. the theoretical mathematical model of a dipole that I, and the industry for the past 60 years have used.
The dipole halves the radiation pattern, therefore it DOUBLES the power in the remaining radiation pattern. Double power is a 3dB increase.
Again, it appears that the recent wireless industry and the changes to terminology made by marketing folks have caused you some confusion. I still use the terms that come from the original science of radio and antenna design. Even going back to my 1961 edition of the Radio Ameteur's Handbook, a fairly recent document in the course of my career, isotropic is treated like an omnidirectional radiator.
--
Take care,
Mark & Mary Ann Weiss
Hear my Kurzweil Creations at: »www.dv-clips.com/theater.htm
'»www.mwcomms.com/auctions.htm
'»www.mwcomms.com
'»www.adventuresinanimemusic.com
| |
DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| said by 91439306 :Popular in what era? Back in the 50s and 60s (and even into the 70s) when I designed antennas for VHF broadcast applications, the common term for omnidirectional was 'isotropic radiator'. The closest antenna to being an isotropic radiator in today's market are the ERI 'rototiller' circularly-polarized FM broadcast antennas so commonly in use. Google is your friend.
»www.google.com/search?hl=en&lr=l···+Antenna
Mind you, I am only fifty three years old and I am not an EE, I am a mere Computer Scientist so I may have to defer to your somewhat "dated" meanings for terms.
said by 91439306 :... It seems the industry has redefined the language of science and engineering. Most likely the marketing branches of various manufacturers. We agree upon that, at the least.
said by 91439306 :Your model of the 2.17dBi dipole may take into account certain factors like conductivity of ground, capacitive coupling and other real world factors that affect actual gain, vs. the theoretical mathematical model of a dipole that I, and the industry for the past 60 years have used. Again Google is your friend.
»www.google.com/search?hl=en&lr=l···fine:dBd
It seems that 2.17 dBi is a bit more than the industry now accepts. My bad.
said by 91439306 :The dipole halves the radiation pattern, therefore it DOUBLES the power in the remaining radiation pattern. Double power is a 3dB increase. Understood but a dipole does not really halve the area of the pattern. It is convienent to use 3 dBi as the gain of a dipole as it is easy to use in computations, but the the gain of a "resonant half-wave dipole" in the real world (and as used by the industry today) is somewhat less than 2.5 dBi.
said by 91439306 :Again, it appears that the recent wireless industry and the changes to terminology made by marketing folks have caused you some confusion. Not at all. My training in antenna theory comes from my training in the service cryptologic agencies back in the early 70's and even at that time I was told a dipole had 2.2 dBi gain.
said by 91439306 : I still use the terms that come from the original science of radio and antenna design. Even going back to my 1961 edition of the Radio Ameteur's Handbook, a fairly recent document in the course of my career, isotropic is treated like an omnidirectional radiator. Time to get the newer literature. I have some books here which are somewhat dated as well. I have, for example, the original "antenna handbook" by Ken "Judge" Glanzer, K7GCO, "Volume 1, Theory and Practice, 1966" of which I am quite fond because of the things I learned about terminated long wire antennas and used in the field of applied Electronic Warfare  . Mind you the oldest copy of the ARRL Antenna Book I have is dated 1974 and it weighs about one fifth of the 19th Edition ARRL Antenna Book I have dated 2000. There are the other mandatory readings I have handy, "Microwave Experimenters Handbook", "ARRL Handbook for Amateurs" but you get the idea.
Here is another great resource if you have not already found it.
»www.w1ghz.org/antbook/preface.htm
Whatever....
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