[Antennas] Unity Gain?

[dtx]

And here in the Los Angeles area we have the opposite condition:  
4-7,000 ft mountains ringing the basin and it is very easy to drive on 
major freeways where the angle to the repeaters are 20 to 40 degrees 
above the horizon and with a little effort you can drive on streets 
where it gets close to  60 degrees.  We found the center loaded gain 
antennas of no real value and a quarter wave spike in the middle of the 
roof worked better overall, looked better and didn't hit support beams 
in parking garages.  With that said, most of us had such a gain antenna 
in the trunk to put on for long trips out of the area, e.g. Las Vegas or 
the Colorado river.

More directly to the original question, all gain is referenced to 
something.  Common ones are dbi for an isotropic radiator and dbd for a 
reference dipole.  I think dbu is for a microvolt across a 75 ohm load 
(and probably invented so that cable TV techs don't have deal with 
negative numbers   Is -84dbm greater or less that -89dbm kind of thing 
;-)  dbV is 1 volt across a 600 ohm load, common in audio broadcast and 
recording situations.

So in reality, a unity gain antenna statement without the reference is 
almost an oxymoron such as "Come on down and have a free lunch" or the 
dentist telling you "This won't hardly hurt at all."  For VHF and UHF 
mobile antennas, the position and efficiency are probably going to be 
more  important than some one's gain claim.

And then there is the mysterious "much less gain" measurement referred 
to by the first David<G>  How did you take that measurement?  With 
instruments on a test range?  Switching antennas and listening to one 
repeater sitting still in your driveway?  Driving to and from work over 
your normal route and talking on the usual repeaters and getting 
noticeably worse mobile flutter or unable to get into some repeaters?  
Or maybe I am entirely wrong assuming you are running a VHF or a UHF FM  
station in your mobile installation.  We don't usually hear of  someone 
running 1/4 wave antennas mobile on 10GHz or 40M sideband but it could 
happen maybe ;-)

If we knew the make and model of the antenna in question, perhaps there 
would be a website that could shed light on just how THEY arrived at 
that unity gain claim.

Gary WA6DTX

DavidE Benedict wrote:

>k6mhe at adelphia.net writes:
>  
>
>>From time to time an antenna manufactures will state that an antenna has 
>>"unity gain". It is my understanding that this term is used for
>>describing 
>>antennas used in mobile applications and is referenced to the gain of a 
>>quarter-wave whip.
>>Does anyone know of any instances where this term is used otherwise?
>>
>>My reason for asking is that I have a so called unity gain antenna, but 
>>when comparing it to a standard quarter-wave whip it has much less gain.
>>
>>Danny, K6MHE
>>     
>>
>>- - - 
>>
>>Your moderator for this list is:
>>Larry Wilson KE1HZ antennas-owner at mailman.qth.net
>>_______________________________________________
>>Antennas mailing list
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>>    
>>
>
>I am not able to be your expert, but I do have one insight.
>
>When comparing antennae it is often necessary to consider their radiation
>pattern. For many applications the spherical or donut pattern of the
>classic 1/4 wave vertical is not  such a great idea. For instance, why do
>I want wasted signal going up into the stratoshpere when I am only trying
>to reach repeaters between me and the radio horizon? I don't want or need
>that. A 5/8 wave does a much better job for me, for it "seems" to give me
>gain because it concentrates its radiation in the lower angles, ...but I
>miss talking to the airplanes near and way above me (if that's important
>to me.)
>
>Just a thought.
>
>David B
>w7dbh
>Beaverton, Oregon
>
>David B.
>
>- - - 
>
>Your moderator for this list is:
>Larry Wilson KE1HZ antennas-owner at mailman.qth.net
>_______________________________________________
>Antennas mailing list
>Antennas at mailman.qth.net
>http://mailman.qth.net/mailman/listinfo/antennas
>
>  
>