On Mon, 27 Apr 2009 19:12:10 -0500, "MikeWhy"
wrote:


"LRod" wrote in message
.. .
On Sun, 26 Apr 2009 17:47:02 -0500, "MikeWhy"
wrote:

"Art Greenberg" wrote in message
news:49udnSEkFIc5SGnUnZ2dnUVZ_tidnZ2d@supernews .com...

A dipole is also somewhat directional, with about 2 dB of gain in its
broadside direction compared to a point radiator. This implies the
same 2 dB attenuation in its side lobes, off the ends.

A dipole is not "somewhat directional"--it's absolutely directional.
It has its major lobes perpendicular to its axis. It has extreme nulls
off the ends. It is, by definition, directional.

I think you're referring to an isotropic radiator? The gain of a dipole
(folded or not) is around 3dbi IIRC. This is the ideal gain broadside to
(perpendicular to) the antenna. The actual gain will be very much a
function of height above ground, the conductivity of the ground, and the
proximity and type of of surrounding opjects.

The gain "off the ends" can be very low, much worse than 2 or 3db below
the maximum.

A dipole has no gain. In fact, it is the real world reference to which
other antennas are compared to determine their gain. The isotropic
radiator, while interesting to consider in a theoretical sense,
doesn't (and can't) exist. While useful for theoretical modeling, it's
sole purpose in the real world is to make an antenna with gain (Yagi,
LPDA, rhombic, etc.) seem like it has more gain by making the
comparison not legitimately to a dipole, but hyperbolically, to an
isotropic radiator.

Since we care about nits today, 2.15 dBi, actually, and not entirely
applicable due to the parasitic coupling you mentioned. The end nulls will
certainly be considerably different from a simple wire dipole because the
end current nodes do not fall to zero as they must on the simple wire.

Nothing more amusing to me than to see the theoretical dBi (decibels
of gain in reference to an isotropic radiator, which doesn't exixt)
applied to a dipole. Geez, it's a dipole. It has no gain. dBi,
particularly when discussing a dipole, is essentially a worthless
"value." And to further make the point, when one tosses out the
calculated dBi, the antenna used as a reference is almost universally
the dipole (dBd). That's why it's so amusing. One might as well say a
dipole has zero gain when compared to a...dipole. Duh! can anyone
spell tautology?

Zero similarly doesn't exist in older number systems. Even they learned the
errors of their ways, or at least succumbed to natural selection pressures
in their own way.


Dipoles have non-uniform directivity.

???

It would make a lousy basis of reference.

Yet it's the principal basis of reference that's used in the real
world of antenna performance measurement. dBi only has relevance in
marketing.



--
LRod

Master Woodbutcher and seasoned termite

Shamelessly whoring my website since 1999

http://www.woodbutcher.net
http://www.normstools.com

Proud participant of rec.woodworking since February, 1997

email addy de-spam-ified due to 1,000 spams per month.
If you can't figure out how to use it, I probably wouldn't
care to correspond with you anyway.

"LRod" wrote in message
...
On Mon, 27 Apr 2009 19:12:10 -0500, "MikeWhy"
wrote:


"LRod" wrote in message
. ..
On Sun, 26 Apr 2009 17:47:02 -0500, "MikeWhy"
wrote:

"Art Greenberg" wrote in message
news:49udnSEkFIc5SGnUnZ2dnUVZ_tidnZ2d@supernew s.com...

A dipole is also somewhat directional, with about 2 dB of gain in
its
broadside direction compared to a point radiator. This implies the
same 2 dB attenuation in its side lobes, off the ends.

A dipole is not "somewhat directional"--it's absolutely directional.
It has its major lobes perpendicular to its axis. It has extreme nulls
off the ends. It is, by definition, directional.

I think you're referring to an isotropic radiator? The gain of a
dipole
(folded or not) is around 3dbi IIRC. This is the ideal gain broadside
to
(perpendicular to) the antenna. The actual gain will be very much a
function of height above ground, the conductivity of the ground, and
the
proximity and type of of surrounding opjects.

The gain "off the ends" can be very low, much worse than 2 or 3db
below
the maximum.

A dipole has no gain. In fact, it is the real world reference to which
other antennas are compared to determine their gain. The isotropic
radiator, while interesting to consider in a theoretical sense,
doesn't (and can't) exist. While useful for theoretical modeling, it's
sole purpose in the real world is to make an antenna with gain (Yagi,
LPDA, rhombic, etc.) seem like it has more gain by making the
comparison not legitimately to a dipole, but hyperbolically, to an
isotropic radiator.

Since we care about nits today, 2.15 dBi, actually, and not entirely
applicable due to the parasitic coupling you mentioned. The end nulls
will
certainly be considerably different from a simple wire dipole because
the
end current nodes do not fall to zero as they must on the simple wire.

Nothing more amusing to me than to see the theoretical dBi (decibels
of gain in reference to an isotropic radiator, which doesn't exixt)
applied to a dipole. Geez, it's a dipole. It has no gain. dBi,
particularly when discussing a dipole, is essentially a worthless
"value." And to further make the point, when one tosses out the
calculated dBi, the antenna used as a reference is almost universally
the dipole (dBd). That's why it's so amusing. One might as well say a
dipole has zero gain when compared to a...dipole. Duh! can anyone
spell tautology?

Zero similarly doesn't exist in older number systems. Even they learned
the
errors of their ways, or at least succumbed to natural selection pressures
in their own way.


Dipoles have non-uniform directivity.

???

It would make a lousy basis of reference.

Yet it's the principal basis of reference that's used in the real
world of antenna performance measurement. dBi only has relevance in
marketing.

Is the radiation pattern of a dipole uniform in all directions? If not,
which single gain value would you use for as the base reference gain? You
have this completely backwards. Marketing benefits from a single figure of
merit, some "gain" value over a dipole or some other value. It makes sense
to you and me as some indication of its performance in presumably the
forward direction.

Antennas are passive devices. Forward gain comes from accepting energy from
one direction while rejecting energy from other directions. (Simplisticly
speaking, since nits count.) By itself, it says very little about the
antenna. The single figure of merit is meaningful mostly for marketing. A
picture here is worth a few thousand words. Have a look at
http://www.eznec.com/.

On Tue, 28 Apr 2009 04:08:39 -0500, "MikeWhy"
wrote:

"LRod" wrote in message
.. .
On Mon, 27 Apr 2009 19:12:10 -0500, "MikeWhy"
wrote:


"LRod" wrote in message
...
On Sun, 26 Apr 2009 17:47:02 -0500, "MikeWhy"
wrote:

Yet it's the principal basis of reference that's used in the real
world of antenna performance measurement. dBi only has relevance in
marketing.

Is the radiation pattern of a dipole uniform in all directions? If not,
which single gain value would you use for as the base reference gain?

If you don't understand the concepts of antennas (dipoles in
particular) and lobes, there is no point in discussing this further.

Go buy those antennas with 2.1 dB more gain (*calculated*
against...thin air) than the identical product of their competitor
(*measured* against a real life antenna)r. You're a perfect subject
for their market.



--
LRod

Master Woodbutcher and seasoned termite

Shamelessly whoring my website since 1999

http://www.woodbutcher.net
http://www.normstools.com

Proud participant of rec.woodworking since February, 1997

email addy de-spam-ified due to 1,000 spams per month.
If you can't figure out how to use it, I probably wouldn't
care to correspond with you anyway.