Re: UNUN Cores?How To Wind?

Thanks for all the information.

The 9:1 works with 8 turns trifilar, on the FT240-67 from 80 through
to 10 meters. Its poor on 160 meters.

All the cores are FT 240 size from Amidon or Bytemark. I can get the
transformers to work but only over a narrow frequency range for the
higher impedance ratios.

I notice that the Sevick UNUN thats sold by Bytemark, a 18:1 ratio
is narrow band and wont cover 1.8mhz to 30 mhz. Anyhow i dont have
the magic recipe yet but I will keep experimenting.


Bob



amdx wrote:
"Greg" <bluehyhena@xxxxxxxxxxx> wrote in message
news:22e47242-3660-4bb4-9406-fab7333e915f@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi

I am trying to build a broadband UNUN 9:1 from 1.8 mhz to 30mhz. I
have had no luck.

The first one the that I built, I used #67 material
snip

The question is simply how do I build a broadband UNUN or
Autotransformer from 1.8mhz to 30mhz and what core do I use? I am
coming to the conclusion that these auto transformers or high
impedance UNUN's are narrow band devices?

I am playing around with a terminated T2FD type antenna trying
different impedances, 450,600,800 and 1000 ohms termination resistors.

Bob

Here are some papers that may help.
http://www.hep.princeton.edu/~mcdonald/examples/EM/sevick_hfe_4_1_46_05.pdf
http://standards.ieee.org/reading/ieee/ept/trans.pdf

These came from here, there are others.
http://unjobs.org/authors/jerry-sevick

Mike
.

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