David
I think you can help me out on this efficiency malarkey. A dipole receives
all signals within the dipoles range so its receive capabilities are well
beyond
the frequency span of choice
I would venture to say that when discussing efficiency we should place
bandwidth of choice received divided by the total bandwidth that the dipole
actually receives and then multiply by 100. To say a dipole is 90 %
efficient when some parts of a dipole supply radiation that is many times
its other parts of equal lengths supply demands further explanation. Maximum
radiation can only come about when the current flow is a maximum regardless
of current input and is a constant per unit length and that description does
not match a dipole which always require added insertion losses for equipment
to overcome its inefficiences. If the dipole exceeds 90% efficiency then why
waste effort and energy on interface devices between the antenna and the
transformation to say.... audio?
Efficiency should always be aimed at the energy needs required over the
total energy
that has to be supplied to meet required needs. If a truck carries a grain
of desired gold buried in a ton of junk would you call the mining operation
100% efficient by ignoring search costs of finding the grain of gold and the
removal costs for the junk? I believe the above verifies my initial
statement that a dipole can be seen as inefficient. As an engineer I cannot
agree
with power in versus power out ( radiation) type statements as energy
cannot be created or destroyed. Energy supplied by a lump of coal does not
lose any energy in its change of state but as far as efficiency is concerned
I do not count the energy that escaped in smoke as beneficial
and thus quantified as a positive with respect to efficiency
Regards
Art



"Dave Shrader" wrote in message
news:_ozZb.356634$I06.3765208@attbi_s01...
Guys, you're off on a tangent!

I believe Efficiency is the ratio of power radiated to power input.

If a dipole is 95% efficient it radiates 95 out of 100 watts.

If a Yagi is 95% efficient it radiates 95 out of 100 watts.

If a Quad is 95% efficient it radiates 95 out of 100 watts.

If a vertical is 95% efficient it radiates 95 out of 100 watts.

If a Log Periodic is 95% efficient it radiates 95 out of 100 watts.

If a 1/10 wavelength antenna made of unobtainium is 95% efficient it
radiates 95 out of 100 watts.

Don't confuse Gain, Directivity and Efficiency in the discussion.

Deacon Dave

Richard Harrison wrote:
Art, KB9MZ wrote:


SNIP

In any case, "efficient" is only as compared with similar devices.

SNIP: Wrong!! See above

Recall that dBd is the norm as an isotropic antenna is only a
theoretical creature. Catalogs are filled with antenna characteristics
as compared with a 1/2-wave dipole in free space.

SNIP: The comparison is generally Gain as dBd, dBi, or dBu
[unobtainium]. Not Efficiency!!!

It is the standard of
comparison. It could hardly be correctly called inefficient.

Best regards, Richard Harrison, KB5WZI