The more I thought about it, the less I liked a vertical in free space
as there is no ground in free space to drive the vertical "against".
Also in my previous comparison the power delivered to the antennas was
not adjusted to be equal.
I redid the experiment with a vertical over perfect ground compared to a
vertical dipole in free space. Both antennas were adjusted to resonance
at apx 7MHz and the vertical was fed over perfect ground with 1amp
current. The current in the vertical dipole was adjusted such that the
power delivered to both antennas was the same (0.715amps, probably
should be 0.707!). This yields the following results:
1. max gain of vertical with perfectly conducting ground (which
occurs at zero degree azimuth) = 5.15 dbi
2. max gain of vertical dipole in free space (which also occurs at
zero degrees aximuth) = 2.13 dbi
I believe there's a weakness in this argument... my suspiscion is that
it's related to setting the power delivered to both antennas as equal.
That said, I can't figure it out at the moment and it sure seems the
power should be equal, after all your transmitter doesn't know what
antenna is out there!
Oh well, when I get it figured out, if anyone still cares I'll post it!
This thread may have gotten a little esoteric anyway.
73's
chris, n4vi
|