Building it was easy. Designing within the limitations was a little more
difficult. Actually, since the higher power baluns have some size to them due
to the cores they were easier to wind than some of the smaller ones I have made.
In this case I was only concerned with 50:200 ohms, high power (15 kW), and had
to cover 150 kHz to as high as I could get it to go. If I couldn't get it to
20 MHz I was going to have to do the span in two different transformers. It
was never going to see the outside elements and only had to last for a couple
of days. I ended up pulling a turn off the initial design and bringing the low
end roll off right to 150 kHz but being able to extend the high end to above 20
MHz. Worked well for the purpose of our test.
Like you said, most hams think that a 4:1 balun that covers from 1-54 MHz at
1500 watts will match 10 ohms to 40 ohms, 50 ohms to 200 ohms, or 100 ohms to
400 ohms with equal zeal. If only it were true.
I wouldn't even get into the antenna pattern discussion but at least if the
transformer is doing its job you would be dumping your max power to the antenna
regardless of how crappy a radiator it is and hopefully decoupling the feedline
from the antenna as well..
Earl
N8SS
--- richard@karlquist.com wrote:
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
To: kz8e@wt.net, towertalk@contesting.com
Subject: Re: [TowerTalk] Fair rite materials for choke baluns
Date: Mon, 4 Jul 2016 19:37:50 -0700
On 7/3/2016 5:53 PM, Earl Morse wrote:
> Wide band, high power transmission line transformers are difficult to make.
> Earl
> N8SS
>
It's not so much that they are hard to make: I have a 50 ohm to
450 ohm transformer that works well from 1.8 to 54 MHz at the
kilowatt level. It was difficult to design, but it is not
difficult to make. The problem is that it ONLY works from 50 ohms
to 450 ohms. It is not a general purpose 9:1 impedance
transformer, that can, for example, transform 10 ohms to
90 ohms. Where people get into trouble is when they are
driving some wire antenna over many octaves of bandwidth
and the impedance is all over the place (not to mention the
antenna pattern).
Rick N6RK
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