View Single Post
  #34   Report Post  
Old March 23rd 05, 12:25 AM
K7ITM
 
Posts: n/a
Default

"John Smith" wrote, " Rather, I was looking for antennas which
preformed better than the poor preformance which standard theory would
suggest--..."

Perhaps you're thinking of different antennas than I have in mind right
now. But using simple resonant half-wave dipoles or quarter waves over
ground planes, it seems to me the performance is pretty amazing.
Consider that under the right HF skip conditions, you can communicate
half way around the world with such antennas, fairly simple receivers,
and just a few watts of RF. Put the same amount of RF into a
transmission line made of copper wires and consider how far it gets
before the power is too low to be useful for communications. Even if
your transmission line were extremely low loss (say 2.5cm diameter
wires forming a 600 ohm line, giving about 0.15dB/mile at 4MHz), in
under 2000 miles, you wouldn't have enough power left on the line to
give reliable communications. And the antenna-radiated RF would be
detectable over a wide area, not just at the output of a transmission
line. Even fairly small antennas, half or a quarter the size required
for unloaded resonance, can be efficient enough to allow pretty
remarkable transmission of RF energy. In fact, the inefficiencies of
small antennas generally come about in the matching systems much more
than in the radiating structure itself. So I'm left wondering just why
you think antennas that perform as "standard theory" suggests are
performing poorly.

Or perhaps you're considering the difficulty of concentrating the
radiation in a certain direction using small antennas...though I would
not have thought that from your base posting.

Cheers,
Tom