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Re: [TowerTalk] Cage dipole revisited.

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cage dipole revisited.
From: Steve Hunt <steve@karinya.net>
Date: Sat, 11 Apr 2009 19:22:10 +0100
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Dan,

More eloquently put than I could have - I agree entirely!

The 5dBd figure can't be passed off by saying they might be referencing 
a dipole in free space. Take a look at the advertising. The 5dBd figure 
refers to "actual testing", and operators getting reports "all the time 
of 2 "s" units difference". What can that mean if it's not side-by-side 
comparisons?

Like Dan I was contacted by PM by this company. I was admonished for not 
understanding what "radiation resistance" is. The advertising claims: " 
The cage antenna has 1/6th of the radiation resistance of a standard 
dipole antenna". Interesting that it should be one sixth - corresponding 
to the number of wires in the cage!! I'll leave you to judge who really 
understands "radiation resistance" and who doesn't.

I'm generous enough to think that the ludicrous claims are down to 
misunderstandings rather than a deliberate attempt to mislead. It's a 
shame - a cage dipole has  merit, and shouldn't need advertising "hype".

Steve G3TXQ


Dan Zimmerman N3OX wrote:
>>
>>  Really?
>>
>> Do you know of a product that would allow me to mount my comparison dipole
>> in free space for tests?
>>
>> To use dBd to refer specifically to a dipole in free space is misleading
>> marketing BS.
>>
>> If antenna makers were interested in clear reporting of their products
>> specifications, dBi would be the only gain number specified with respect to
>> an ideal theoretical source.  I know that it is not always used this way,
>> but when dBd gain is published, it should express the gain over a dipole
>> mounted at the same height over the same earth conditions.
>>
>> It's no fair trying to claim that dBd means "gain over a dipole in free
>> space"  The clear, misdirection free use of dBd is "gain over a dipole in
>> the same location."  That has meaning and is a useful gain measurement,
>> because it automatically subtracts out any ground gain advantage.
>>
>> A dipole has zero dBd gain no matter where you install it.  I know some
>> disagree with that, but it doesn't make one bit of sense to use it at ALL
>> otherwise.
>>
>> You want to refer to the gain including ground gain of some installation,
>> use dBi.
>>
>> 73
>> Dan
>> _______________________________________________
>>
>>
>>
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>>
>>     

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