| |
G8MNY > TECH 12.07.03 23:16l 28 Lines 1138 Bytes #999 (0) @ WW
BID : 5393_GB7CIP
Read: DF6DBF DB0FHN GUEST OE7FMI
Subj: Coax Balun
Path: DB0FHN<DB0RGB<OK0PPL<RZ6HXA<HA3PG<IK1ZNW<EA7URC<GB7CRV<GB7CIP
Sent: 030712/2027Z @:GB7CIP.#32.GBR.EU #:5393 [Caterham] $:5393_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
This type of balun is to be found in most textbooks & many aerial designs.
Balun is 1/4 wave of scrap coax alongside the feeder.
-------------
B -@! dead coax ! @=Solder
! ============@------------------
\[ Feeder
B ---------------------------------
The feeder inner is connected to the dead coax braid BB are the 50 ohm 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
1/4 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 +/- voltage
phases appear to radiate equally from both halved of the balanced 1/4 wave
lines & hence cancel, the 2 balanced folded 1/4 waves look like a 1/2 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.
/QSL
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
