Danny Richardson wrote:
A very narrow range peaked at about 1.58 MHz. (The unit's rated
frequency range is 1-30 MHz.)

I once bought a commercial 4:1 balun wrapped on a
type 2 powdered iron core rated for "all-HF" operation.
The performance sucked. I had the factory measure the
choking impedance and it did indeed suck. Sorry, I don't
remember the exact results but it was designed by Jerry
Sevick, W2FMI, and described on page 34 of "Building
and Using Baluns and Ununs".
--
73, Cecil http://www.w5dxp.com