Balun for PI network antenna tuner
 

Another ham gave me a homebrew PI network tuner he used to tuning
single wire feed antennas. I'm planning to build a multiband antenna
and feed it with twinlead or ladder line since it's less lossy than
coax.

I'd like to make or buy a balun for this tuner. I don't plan to run
more than 100 watts, and will probably start experimenting with QRP
operating as well.

Any guidance is appreciated.

Red

Red,

Well, a balun at the antenna side of the tuner is what most people would do.
Unless you use a link coupled or double balanced tuner, there really isn't much
else of an alternative. 1:1, 2:1, 4:1, 9:1 or what? Well, you're going to see
quite large impedance changes based upon what antenna you use and what bands
you operate. You'll likely get a good match on some bands and not so good on
other bands. I'd recommend a 4:1 balun as a compromise.

And don't forget those HF swap nets.

Best of luck and 73s,

Evan, K9SQG

You will need a 1:1 choke balun between the tuner and the balanced feedline
to the antenna.

Obtain an HF-quality ferrite ring, about 1.75 inches in diameter.
Permittivity around 200-400.

Wind on 8 or 10 turns of 18 or 20 gauge, stranded, flexible,
figure-of-eight, twin speaker cable.

This should cover the range 1.8 to 30 MHz.
----
Reg, G4FGQ

Reg,
I'm afraid your "figure-of-eight" lost me. What's
that?
'Doc

Here in the states we would call it lamp or Zip cord.


--
John Passaneau, W3JXP
Penn State University



"'Doc" wrote in message ...


Reg,
I'm afraid your "figure-of-eight" lost me. What's
that?
'Doc

Figure-of-eight . . . .

Two circles stuck together. Outline of plastic insulation surrounding a
pair of close-spaced wires.

Zip-cord ?
---
Reg



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"'Doc" wrote in message ...


Reg,
I'm afraid your "figure-of-eight" lost me. What's
that?
'Doc

Is lamp or zip cord twisted with a fairly short lay?

The stuff I have in mind for baluns lays flat. Colourless. It may be sold as
speaker cable.

It has lower copper loss then coax, easier waterproofed and constructed.
----
Reg

===========================

Here in the states we would call it lamp or Zip cord.

Reg Edwards wrote:

Is lamp or zip cord twisted with a fairly short lay?

The stuff I have in mind for baluns lays flat. Colourless. It may be sold as
speaker cable.

It has lower copper loss then coax, easier waterproofed and constructed.

Reg, is that superior to coax wound on the same toroid?
I use RG-400 teflon coax for my baluns.
--
73, Cecil http://www.qsl.net/w5dxp



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Reg,
Okay, now I understand what you're talking about.
For a while there, I thought you may have been talkng
to Mr. Moebus...?
'Doc

Reg, is that superior to coax wound on the same toroid?
I use RG-400 teflon coax for my baluns.
--
73, Cecil http://www.qsl.net/w5dxp

============================

Just compare the coax inner conductor diameter with the 18-gauge wire of the
zip-cord. Conductor resistance is inversely proportional to wire diameter.

Furthermore, the transition from 50-ohm to open-wire line is less abrupt.
In theory, the impedance of the line wound on the transformer should be
intermediate between coax Zo and open-wire Zo.

On the other hand, the difference in loss due to either effect is hardly
detectable. The length of line involned is too small to make much
difference. I shouldn't bother changing the design.

I can't imagine how the coax got in there in the first place.
---
Reg, G4FGQ