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G8MNY  > TECH     03.12.18 11:30l 39 Lines 1216 Bytes #1 (0) @ WW
BID : 47694_GB7CIP
Read: GUEST
Subj: Coax Sleeve Balun
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 181203/1019Z @:GB7CIP.#32.GBR.EURO #:47694 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
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 made from ¬ wave lengths of scrap coax (longer needed to cover the
fatter outer) braid or pipe over the top of the feeder. It is electrically
connected to the coax braid 1/4 wave from the balanced feeder connections.

          ÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
BALANCED  ÚÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
      BÄÄÄ)                   UNBALANCED  FEEDER
      BÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
          ÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

This works by hiding the unbalanced outer aerial connections from the outside
world so it can't radiate.

In practice I recommend heatshrink sleeving & heat glue it used to seal the add
outer section.

Common mode Z is only high at the resonant frequency, where it eliminates any 
outer feeder current on the unbalanced coax.

   Z
Hi ³      .".
   ³     /   \
Low³...-'     `-.....
   ÀÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ F
           Fo


Why don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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