[Antennas] Unity Gain Rephrased Question

[A10382]

Want to start a 'hot' tread or burn up a net?  Just start a conversation
about one of the hot topics.  And "ANTENNA GAIN" is about as hot as any
other.
----------------
Whenever you hear the word 'gain', you should be asking "Gain? Compared
to what ?"

"Unity Gain" means the antenna produces the same ERP (Effective radiated
power) as whatever it is referenced to.  'Gain', expressed in decibels
(dB), is a comparative measurement, NOT a quantitative one.

In the mobile / portable (HT) radio business that 'reference' antenna
has been, by convention, the ubiquitous 1/4wl vertical with ground
plane.

For base stations, the referenced antenna is that 1/4wl vertical
w/ground plane for comparing vertically polarized ones and the 1/2wl
wire horizontal dipole, mounted 1/2wl high over 'average' quality ground
for comparing horizontally polarized antennas.

-----

When comparing horizontal antennas (wire dipoles, yagis, multi-element
'beams', log periodic, 'zepps', etc.), 'gain' again is comparative and
is usually referenced to the 'standard' 1/2wl horizontal wire dipole.
Unfortunately, there are two environments for this:
1) a 1/2wl horizontal dipole mounted 1/2wl high over 'average' ground
(normally slightly moist earth)
2) a 1/2wl horizontal dipole mounted in free space (the isotropic
sphere).

The difference in these two can be as much as 2.1db (3dB is  2x !)  and
this spec is mis-stated by some manufacturers in the fine print, making
their antennas seem better than they really are.
Imagine that!  A marketing person stretching the spec!  How unusual !

The only important thing is that the antenna being speced is
measured/compared the very same way to the referenced one.  Again,
'gain' is only a comparison and  does NOT add or amplify RF  power - it
only focuses the radiated power where you want it - like the lens behind
a flashlight bulb compared to a bulb hanging from it's cord.

Whenever you hear the word 'gain', you should be asking "Gain? Compared
to what ?"

====
73, Frank
 ._._.


----- Original Message -----
From: "Dan Richardson" <k6mhe at adelphia.net>
To: <antennas at mailman.qth.net>
Sent: Wednesday, June 23, 2004 4:03 PM
Subject: [Antennas] Unity Gain Rephrased Question


> I sorry but I see that I was unclear in my unity gain question so let
me
> try again.
>
> In the mobile radio service industry is it normally accepted that the
term
> an antenna has "unity gain" means that the antenna is referenced to
have
> the same gain as a 1/4-wave whip?
>
> I'm not seeking the definitions or explanations of "gain" other than
how
> the term "unity gain" is used in the mobile radio business.
>
> I had been told, at one time, by a technician (non-ham) that in the
mobile
> radio business "unity gain" and the gain of a 1/4-wave monopole (whip)
was
> the same and I am trying to ascertain if that statement is valid.
>
> 73
> Danny, K6MHE
>
>
> - - -
>
> 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


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