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Date: Thu, 10 Jan 2002 20:01:57 -0700
To: k2 <elecraft at mailman.qth.net>
From: mike <kw1nd at homeinternet.net>
Subject: [Elecraft] Semi OT:  ratios of unun windings

Good evening, all.  I'm in the process of beginning to experiment with a 
wanna-be Beverage, and had a question about winding an unun for 
it.  Through the ARRL Handbook & Amidon's literature, I've calculated the 
number of primary & secondary turns needed for the chosen core.  BTW, the 
antenna is for LF, receive only.

I've come up with a ratio of 18:54 turns (50 ohms:500 ohms).  Is it 
permissible to reduce this to 9:28, or even 3:9?  As in, I assume the magic 
isn't in the exact number of turns, but rather the ratio between primary & 
secondary windings.  Although 1:3 would be the next step, I get the feeling 
that this would not allow for adequate coupling between the 
windings.  Working the formulas backwards, the 3:9 actually turns out to be 
a 50 ohm:450 ohm match, which is still adequate for my testing (since the 
impedance of the antenna at LF is only an estimation anyway, and is only 
for receiving).

Does all this make sense?

73,

Mike Boice, KW1ND
Nampa, Idaho

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From: alta <alta at alta-research.com>
Reply-To: alta at alta-research.com
Organization: Alta Research
To: <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Semi OT:  ratios of unun windings
Date: Thu, 10 Jan 2002 23:14:59 -0800


Mike ...

It makes sense to me.  And may not be too critical for LF 
receive-only.

For HF transmitting, I know that other important factors are: the 
spacing between the tri-filar conductors and wire size (the resulting 
impedance), core material, core size, and number of turns for the 3 
windings.

... Reed

On Thursday 10 January 2002 19:01, you wrote:
> Good evening, all.  I'm in the process of beginning to experiment

> -- snip --

> 73,
>
> Mike Boice, KW1ND
> Nampa, Idaho

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Date: Thu, 10 Jan 2002 23:36:50 -0800
From: "John Grebenkemper, KI6WX" <KI6WX at pacbell.net>
Subject: Re: [Elecraft] Semi OT:  ratios of unun windings
To: Elecraft Mailing List <elecraft at mailman.qth.net>

Mike;
You need to compute the inductance of each winding, and from this compute
the inductive reactance at your operating frequency.  As a rule of thumb,
the reactance should be 10 times greater than the operating impedance of
that winding.  If you are using it for receiving only, you can go below this
somewhat, but if you go too low, the effectiveness of the UNUN will be
reduced and its loss will increase.
-John
 KI6WX


> Good evening, all.  I'm in the process of beginning to experiment with a
> wanna-be Beverage, and had a question about winding an unun for
> it.  Through the ARRL Handbook & Amidon's literature, I've calculated the
> number of primary & secondary turns needed for the chosen core.  BTW, the
> antenna is for LF, receive only.
-- snip --

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