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1. 02:03 PM - interesting antenna discovery (Robert L. Nuckolls, III)
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| Subject: | interesting antenna discovery |
Found a broken WiFi antenna in a box of 'stuff'
a few days ago. Peeled of the outer jacket and
found this inside.
It's a classic 'coaxial' dipole . . . 1/4 wave
radiator and 1/4 wave coaxial sleeve.
The dimensions were a puzzling at first, they
are too short for free space resonance in the
2450 MHz WiFi band.
Then I recalled installing j-pole antennas
fabricated from 450 Ohm 'ladder-line' for a
customer some years ago. I erected radomes
fabricated from PVC pipe and found that when
the antenna was a tight fit in the pipe, proximity
of the dielectric depressed the resonant frequency
of the antenna. The use of 3" PVC and with
cardboard spacers to center the antennas brought
them back to design resonance.
I suspect that's what happens here. The antenna
is physically modified to accommodate proximity
effects of the jacket.
Kinda cool . . .
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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