art wrote:
Cecil Moore wrote:
Actually Art, adding reactance reduces the current in
the element thus *decreasing* losses below what a resonant
passive element would have. Pure reactance is lossless.

Whoa Cecil i dont follow that at all

Resonant passive elements absorb more power
than do non-resonant passive elements. Resonant
passive elements therefore dissipate more heat
than non-resonant passive elements.

With EZNEC, check out the feedpoint impedance
of a two element Yagi when both elements are
resonant Vs when one element is 5% longer and
a non-resonant reflector.

The following values are not optimized by any
means but will give you an idea.

With ten foot spacing between two 33 foot elements

The gain is virtually bidirectional at 10.7 dBi.
The feedpoint impedance is 20 ohms and the current
induced in the passive element is 0.84 amps.

Keeping everything else the same and adding one
foot to the reflector yields the following results.

The gain increases to 11.9 dBi with a F/B ratio
of about 8 dB. The feedpoint impedance is 30 ohms
and the current induced in the passive element is
lower at 0.75 amps.

Making the reflector non-resonant causes its current
to fall by about 0.1 amp thus reducing losses while
the feedpoint impedance has increased by 50% and the
gain has increased by 1.2 dB. There doesn't seem to
be any downside to non-resonant passive elements.
--
73, Cecil http://www.w5dxp.com