On Tue, 13 Apr 1999 11:28:20 -0700 Eric Gustafson <n7cl@mmsi.com> writes:
>
>>> 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 read the antenna book entry for this antenna. They do indeed
>specify a 4:1 balun for feeding this thing. And, it is indeed
>_not_ a T-match or floded dipole element. This discussion has
>exposed my biases. I'm an HF kinda guy. It would never occur to
>an HF antenna designer to match a Yagi driven element as they
>have done for this one. Here is my guess as to how they arrived
>at this configuration.
>
>As I said, this is a _guess_. There are two possibilities. Both
>may or may not have influenced the decision.
>
>1. The antenna was built and optimized for pattern and gain
> considerations. Then, when the matching system decision was
> made, it was desired to match the DE feedpoint impedamce up
> to 200 ohms with a hairpin in order to make it possible to
> use a simple easy to build 4:1 balun which was already
> familiar to most VHF enthusiasts.
>
>2. The antenna was built and optimized for pattern and gain
> considerations. Then, when the matching system decision was
> made, an attempt was made to use a hairpin to get the
> feedpoint impedance up to 50 ohms. But the hairpin
> dimensions turned out to be small relative to the feedpoint
> hardware and therefore fairly critical to get adjusted
> correctly. And still left the feedline decoupling problem to
> solve.
>
>Either way, what they have there should work OK if losses are
>carefully controlled and the thing is weather proofed adequately.
>So my question now is why do you want to use a different
>balancing device than they have specified and provided all the
>dimensions necessary to construct? I can't imagine that the
>ferrite 4:1 balun would be cheaper or more efficient than the one
>shown in the book. If I was doing this and really wanted to use
>a ferrite balun for the feedline decoupling, I'd set the DE and
>hairpin to bring the feedpoint impedance to 50 ohms and use a 1:1
>balun.
>
>73, Eric N7CL
Eric,
The DE mounting method would appear to be marginal for QRO or rain also.
I've built many HF and VHF antennas and would not want to use the
specified phenolic or G-10 in that application. In addition, the
insulated DE is very prone to percipitation static.
After using all of the common DE feed methods, the all metal T Match is
my choice.
The HG66 and old 5el CC are available at fleamarkets, etc for low prices
and high performance modifications have been published.
I've developed a considerable YO file on 6M antennas in general and can
provide full plots and dimensions to anyone interested.
73 Carl KM1H
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