[TowerTalk] Balun(s) Testing

[km1h@juno.com]

>>>
>>> Does the ARRL book really recommend a 4:1 balun with a hairpin
>>> match?  I'd expect this to be a 1:1 balun.
>>
>>Yes, read section 18 of the ARRL Antenna Book.  It is the
>>'Optimized Yagi' for 6 meters
>
>I'll look at the book eventually.  But I'm willing to take your
>word for it now.  It must be a folded dipole driven element or
>something.  A "normal" simple dipole split driven element will
>usually be below 50 ohms at resonance in a yagi of 3 or more
>elements.  The hairpin (or its cousin the "beta") match is used
>to bring the feedpoint up to 50 ohms for the feedline.

It indeed uses a hairpin match, almost a clone of the HiGain 66 which has
been described in several VHF pubs as a rather inefficient performer.
Changing the DE to an all metal T Match as used by CC and the highly
rated K1FO designs would be a better choice and less prone to wx related
VSWR problems.

SNIP


>>I'm not sure what difference this makes.
>
>If they aren't intended for operation above 30 MHz, they may not
>work all that well at 54 MHz.


A lot of the reasons behind balun problems in general and the W2AU 4:1
type in particular were covered in Sevick's book and magazine articles. I
dont have specific details handy.
Going to an optimized toroid core design rather than a lossy ferrite rod
can give excellent performance up thru microwave. However, the best
materials are not always available in sizes suitable for QRO.

A FairRite 67 ferrite mix  or a Micrometals 6 and 7 powdered iron mixes
might be decent starting points for 50MHz.

GL   Carl  KM1H



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