View Single Post
  #360   Report Post  
Old November 12th 03, 02:28 PM
Richard Harrison
 
Posts: n/a
Default

Roy, W7EL wrote:
"When all this is done, I hope that readers come away with some
assurance that circuit theory does work and can be applied to antenna
problems -- provided that the assumotions made for the components are
valid."

Yes. And, there is another proviso. The reflected energy must be
considered along with the incident energy. Antenna problems are
relatives of transmission line problems.

Terman wrote of impedance in a transmission line with a reflection:
"When a reflected wave is present, the impedance will be alternately
greater and lower than the characteristic impedance, as illustrated in
Fig. 4-10."

This is also true of standing-wave antennas but is complicated by r-f
radiation from the antenna.

Early in this thread, I gave the example of W5LIT`s mobile antenna which
was all coil. It was a bamboo pole wound end to end with wire. At the
feed end its impedance was low. Approximately 90-degrees away at the tip
end, impedance was very high as indicated by the corona often produced
by the high voltage.

The current at the tip end was much less than at the feed point. The
ARRL Antenna Book shows how this can happen in Fig 6 on page 16-4 of the
19th edition.

I admire and appreciate Roy`s experimental verification of antenna
speculations and predictions. Until demonstrated, theory is only theory
and all such explanations are not necessarily so.

Best regards, Richard Harrison, KB5WZI