Topband: Two 2:1 transformers to choose from!!

[Charlie Cunningham]

Thanks, Mike!

That's good and useful information!!  I agree that 450 ohms of reactance is
large enough to be "negligibly large" relative to 50 ohms. So Jim might,
indeed, be OK with a 2-turn primary. Of course, he's basically just
constructing a "balun" for his twisted pair to coax transition.  So, he
could probably just wind a twisted pair on a core, for a 1:1 current-mode
balun, and ignore the small mismatch loss.

73,
Charlie, K4OTV

-----Original Message-----
From: kd9sv [mailto:kd9sv at comcast.net] 
Sent: Thursday, August 22, 2013 12:10 PM
To: 'Charlie Cunningham'
Subject: RE: Topband: Two 2:1 transformers to choose from!!

Charlie, on a typical 73-202 binocular core I measure about 450 ohms of open
circuit reactance for two turns so if you make a 9:1 transformer using two
turns pri and 6 turns sec for 50:450 or 75:600 ohms you would have way more
than the recommended 5 times of reactance needed for a good transformer.  
(450 ohms inductive reactance is about 40uHy at 1.85mhz) 73, de gary, kd9sv

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Charlie
Cunningham
Sent: Thursday, August 22, 2013 11:34 AM
To: 'Mike Waters'; 'James Rodenkirch'; 'topband'
Subject: Re: Topband: Two 2:1 transformers to choose from!!

As I recall, Jim is using 73 mat'l cores. I'd be interested to see what sort
of magnetizing inductance he would have looking into the 2-turn primary and
what its reactance is at 1.8 MHz.

Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Mike
Waters
Sent: Thursday, August 22, 2013 11:21 AM
To: James Rodenkirch; topband
Subject: Re: Topband: Two 2:1 transformers to choose from!!

P. 7-69 of Low Band Dxing (5th ed.) by ON4UN says a maximum of 4 turns on
the low-Z primary for binocular cores. It might work, but there are other
turns ratios you might try.

Here is a list of turns ratios for those cores I made:
http://www.w0btu.com/Binocular_core_turns_ratios.pdf
If you get a 500 Server Error message, contact me directly and I'll e-mail
it to you.

73, Mike
www.w0btu.com

On Wed, Aug 21, 2013 at 3:49 PM, James Rodenkirch
<rodenkirch_llc at msn.com>wrote:

> I received enuff "info" and thoughts to know I'll utilize the 5:7 winding
> version.
>
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Topband Reflector

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Topband Reflector