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G8MNY > TECH 25.10.24 07:09z 52 Lines 2043 Bytes #122 (0) @ WW
BID : 18548_GB7CIP
Read: GUEST
Subj: Coiled Choke Balun for HF
Path: SR1BSZ<IW0QNL<IZ3LSV<DB0ERF<DK0WUE<DK0WUE<VK5RSV<K1AJD<KA1VSC<GB7CIP
Sent: 241025/0710Z @:GB7CIP.#32.GBR.EURO #:18548 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
A very practical Balun for HF aerial work is the choke type. It reduces RFI to
& from the feeder & at next to no cost or loss. :-)
This is best placed at the rig end if using balanced feeder or where the coax
is connected to a balance feed & there is a local RF earth on the coax, so the
choke can do it job. E.g. the choke only has to be much higher Z than 25ê.
Placing this type of balun in mid air at the feedpoint is less effective as
then the choke has to be much higher impedance than the free coax outer is!
Balanced Joiner Plastic
ÍÍÍÍÍÍÍÍÍÍÍÍ:ÍÍÍÍÍÍÍ» Tape ÉÍÍÍÍÍÍ(Ä
feeder Block c)))))))))))o PL259
Ferrite Rod
Wind 25 turns or so of bell/LS wire around a 14cm x 8mm ferrite rod from an old
MW radio (or 10 turns on a medium-large sized ferrite ring). Tape it on firmly
to provide some protection against damaging the ferrite.
Collect onto a PL259 plug. Pass one of the stripped wires through one of the
outer case holes, while at the same time push the other one through the centre
pin. Be careful that the heat does not damage the wire insulation when
soldering up.
Put a joiner (2 way block) on the balanced end, so there is no excuse to
throwing the ferrite balun around when /P.
For current isolating baluns to work well, the common mode Z need to be high
compared to the half balanced circuit Z, eg, >250 for 50ê system. This choke is
something like this..
Typical Common mode Z
3k´ __..-..__ Wire
2k´ Straight _..--'" Inter``-._ Length_.
1k´ L _..-'" Winding `-..--'"
500´ _..-'" C
300´_..-'"
ê ÀÄÂÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄ
1.8 3.5 5 7 10 14 21 28 50 70 MHz
See my Tech bul "1:1 HF Balun".
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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