> On 160-40M the number of turns for both the coax and the wire should be 5
> NOT 7. The nominal dia is about 6.5 inches. George used #10 or #12 wire
> NOT #16 in his article in news letter I have.
This design came when people thought voltage baluns were the desirable type,
just before Lewallen W7EL and others started doing balun analysis and
changed the mindset of people to preferring current baluns.
This was the same style used with some Telrex antennas from that time
period. (I scrapped the one from my Telrex 40M Yagi and replaced it with a
current balun).
It's important to know it is a voltage balun, not a current balun. It does
not isolate the shield for common mode problems unless the antenna is nearly
perfectly balanced, so it only should be used when the antenna is nearly
perfectly balanced and nothing excites the cable shield. If you tried to use
it to decouple radials (in an elevated radial vertical), an off center fed
antenna, or with a feedline that doesn't come straight away from a balanced
antenna it would actually hurt the system.
It depends heavily on flux coupling between the single wire winding and the
coax shield for balance. The windings (the coax and the single wire) must be
coupled tightly. The winding must be as compacted as much as possible
without turns being "spread out".
5 turns at 6.5" diameter (plus the continuation of five more turns of coax
shield) would put about 300 ohms XL across the dipole terminals on 1.8,
you'd get by with a slight change in feedpoint impedance. Bill's suggestion
of 7 turns might actually be better.
73 Tom
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