Topband: FT-240-77 Toroid Impedance R + jX Components

[K9AY]

> A while back I posted impedance vs frequency vs # of turns
> data for the Amidon FT-240-77 toroid (Fair-Rite Products
> P/N 5977003801). I have updated my website to include
> plots of the real (R) and imaginary  (jX) components of the
> impedance:
>
> http://FT-240-77.notlong.com
>
> Mike, W4EF......................
______

Good info, Mike

This is close to what I see for 77 material in smaller size toroids and
beads, with some variation in the frequency of peak impedance.  Readers
should not interpret the data as limiting 77 material to any particular
range of frequencies -- it depends on the application the type of
transformer.

The 9:1 transformers I make (TRX-9) use two 3/8" x 3/8" #77 beads
side-by-side to make a quasi-binocular core.  A 3-turn primary and a 9-turn
secondary results in a transformer that covers from below 500 kHz to 30 MHz.
Loss is extremely low for a conventional transformer (separate primary and
secondary windings) -- 0.2 dB typical at 160/80M, measured using two
transformers back-to back and dividing total loss by two.

BTW, I first used this configuration in an output transformer for a 50-watt
2-30 MHz power amplifier (at lower impedance), and have been using it for RX
antennas for several years.

73, Gary
K9AY