G8MNY > TECH 04.12.18 10:45l 43 Lines 1617 Bytes #2 (0) @ WW
BID : 47827_GB7CIP
Subj: Pawsey Stub Coax Balun
Sent: 181204/0938Z @:GB7CIP.#32.GBR.EURO #:47827 [Caterham Surrey GBR]
To : TECH@WW
By G8MNY (Updated Dec 04)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This type of balun is to be found in most textbooks & many aerial designs. It
is a 1:1 balun & does not alter the impedance.
Balun is ¬ wave of scrap coax alongside the feeder (a pipe will do).
BÄÂÄ@ dead coax ³ @=Solder
The feeder inner is connected to the dead coax braid B & B are the 50ê balanced
feed points. The dead coax is what it says, a shorted out at both ends bit that
could even be copper pipe of the same diameter. It is connected to the feeder ¬
wave back from the aerial where the braids join together. At the aerial end the
dead coax is connected to the feeder's inner.
This works by making the aerial connections look "balanced", as the ñ voltage
phases appear to radiate equally from both halves of the balanced ¬ wave lines
& hence cancel, the 2 balanced folded ¬ waves look like a « wave where the
centre is at RF ground & therefore can be connected to the feed coax outer
without any RF left on the outer of the coax skin.
Common mode Z is only high at the resonant frequency, where it eliminates any
outer feeder current on the unbalanced coax.
Hi ³ .".
³ / \ /"\
Low³...-' `-....-' `-.
Fo 3 Fo
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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