Toroid Balun Cores

[Edward R Cole]

Someone mentioned the baluns on older yagis were air-core.  I have an
older Hygain TH3mk4 with original balun (big black box connected to
the hairpin stub and driven element.  The antenna is probably 20-30
years old, so I wonder if anyone can tell me if it is likely air-core
or ferrite?  Any advantage in replacing it?

I found that I had to use a tuner after installing it at 50-feet even
with element lengths adjusted to min SWR per manual.  Now I wonder if
this may be due to an aged balun?

The used antenna only cost me $75 so not a big investment.  But it
does seem to "work" DX OK.  I worked T32 on 10m on Saturday with only
8w SSB from my K3/10.  But eventually I will be running 300w so this
may matter more.

Note that the tuner is required on all bands 20-15-10m.  10m was the
hardest and would not tune very well in any position of the driven
element.  Tuning was done with antenna pointed straight up when at
ground level with reflector essentially at the ground.  I expected
some shift in resonance once the tower was raised (all antennas
installed before raising with a crane).

I suppose this may also point at bad traps (but for $75 it works).


73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-?
DUBUS Magazine USA Rep [hidden email]
======================================

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[John Ragle]

It is a pity that someone back in prehistoric times started using the
word "balun" for two entirely different devices. I use an air core
"balun" (a so-called "choke" balun) which is about a foot long and about
4" in diameter, wound as a single-layer solenoid on PVC pipe, on my HF
beam. This is in place of the scramble-wound "choke" often used at an
antenna feed point.

I also have various matching "transformers" on my 5 beam antennas, none
of which is a toroidal transformer. It is possible to make an unbalanced
line-to-balanced feed point transition without a toroidal transformer,
of course, and when things are managed this way, there is never a
question of a toroid freezing and cracking or alternatively roasting
from too much RF and cracking.

As I see it, one of the truly superior advantages of toroids is as cores
for interstage transformers (or for filters), as in many modern
transceivers. The devices are beautiful because they are physically
small and one can lay them down or against almost any substrate, since
their ultrahigh permeability contains fringing fields completely (any
that are "left over" from imperfections in the flux closure of a perfect
toroid).

John Ragle -- W1ZI

=====

On 10/17/2011 3:14 PM, Ron D'Eau Claire wrote:

> I've never seen an HF Yagi with an air core balun at the feed point. Such
> baluns for HF were typically a foot or more square! (The only ones I ever
> messed with were mounted in the shack to connect a single-ended rig output
> to a balanced feed line.)
>
> By the 1980s ferrite baluns were very commonly used almost everywhere, so
> I'd put money on your having a ferrite balun on that yagi.
>
> If the balun was abused, physically, with too much RF heating or by moisture
> getting into the housing, it may be damaged. The same is true for traps.
>
> 73,
>
> Ron AC7AC
>
>
>
> -----Original Message-----
> Someone mentioned the baluns on older yagis were air-core.  I have an
> older Hygain TH3mk4 with original balun (big black box connected to
> the hairpin stub and driven element.  The antenna is probably 20-30
> years old, so I wonder if anyone can tell me if it is likely air-core
> or ferrite?  Any advantage in replacing it?
>
> I found that I had to use a tuner after installing it at 50-feet even
> with element lengths adjusted to min SWR per manual.  Now I wonder if
> this may be due to an aged balun?
>
> The used antenna only cost me $75 so not a big investment.  But it
> does seem to "work" DX OK.  I worked T32 on 10m on Saturday with only
> 8w SSB from my K3/10.  But eventually I will be running 300w so this
> may matter more.
>
> Note that the tuner is required on all bands 20-15-10m.  10m was the
> hardest and would not tune very well in any position of the driven
> element.  Tuning was done with antenna pointed straight up when at
> ground level with reflector essentially at the ground.  I expected
> some shift in resonance once the tower was raised (all antennas
> installed before raising with a crane).
>
> I suppose this may also point at bad traps (but for $75 it works).
>
>
> 73, Ed - KL7UW, WD2XSH/45
> ======================================
> BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
> EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-?
> DUBUS Magazine USA Rep [hidden email]
> ======================================
>
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>
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> Elecraft mailing list
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>
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>
>

--
Sent from my lovely old Dell XPS 420

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[Eric Swartz - WA6HHQ]

Folks - Let's end this thread as it has more than passed our list
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---
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On 10/17/2011 12:14 PM, Ron D'Eau Claire wrote:
> I've never seen an HF Yagi with an air core balun at the feed point.
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