[Antennas] Low / short wire antennas

2003年3月11日 20:09:09 -0800

1) let's say you have a low horizonal wire antenna, it goes out 13 ft, then 
turns back in the other direction, at a 45 degree to the original wire, for 
another 25 feet. 
A. The whole length does or does not contribute to resonant lenght 
calculation?
B. The book formula will not be totally accurate for this fold back 
antenna?
C. The foldback will to some extent cancel radiation from the longer
part?
D. Is there a formula for actual resonant length for an antenna quite low
to the ground?
2) Where would i find the formula to figure the resonant impedance of
a low horizontal antenna? I was just reading a book on aviation electronics
where it said the series (1/4w) resonance of one typical example of an
aircraft antenna, the radiation resistance was at 5 MHz, 3.8 ohms, contrast
this to the radiation resistance if this wire was vertical, maybe 35-40 ohms.
Thus my interest, in real life yard wire antennas.
Thanks! Hue Miller KA7LXY