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Old November 20th 05, 07:58 PM posted to rec.radio.amateur.antenna
Amos Keag
 
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Default feedlines and strange intereactions

Cecil Moore wrote:
Paladin wrote:

The wires are close. The builder used rotor feed line. 3 equal
lengths of wires 70ft. long
THAT make one element. there is one on the oppisite side.



So like this?

70' 70'
-------------------------+ +-------------------------
| |
+------------------------+ +------------------------+
| |
+------------------------+ +------------------------+
| |
| |
| |
feedline


Hi Cecil, that's what I understand. To a first approximation, on 160
meters, the radiation from the two segments furthest from the feed point
should cancel. That would leave the effective antenna as a shortened
dipole with a length of 55 degrees per leg [two 80 foot long segments
per side]. This should yield a radiation resistance of somewhere around
10 to 15 ohms with a significant capacitive reactance of between 500 to
1000 ohms.

His 100 foot long feed line is only 69 degrees long. I believe this
short a matching section, i.e. "stub", may be insufficient to achieve a
'50 ohm' match.

I would expect the antenna gain to be -2 to -3 dBd.

Comments??