Dan and Bryan,

200 ohms seems too low. I just wound 10 turns on a FT-240-61 core,
single layer occupying about 70% of the core and made the following
measurements of choking impedance on an HP8753 network analyzer in a
calibrated test fixture. The choke was mounted clear of any metal.

14MHz: 220 + j2850
21MHz: 20K
28MHz: 895 - j3.9K

The 10 turns were parallel resonant at 20.9MHz and the calculations for
10 turns would be ~18uH at low frequencies.

The above choke would be very very good from 20 thru 10m.

73,
Larry, W0QE



Bryan wrote:
Daniel wrote:
Hi to everyone,
i need to replace my 1:1 balun on my yagi tribander 14-21-28 Mhz. I
have in my stuff a toroid FT 240-61 and some pieces of rg-142 coaxial
cable. Anyone can help me to know how many winding needs on toroid to
achieve good reactance on 14 to 28 Mhz ?
Thank you ,
Daniel.

I used a dozen turns of RG58 on the same core, and achieved XL ~= 200 ohms
at 14MHz for a Cushcraft A3. RG142 is about the same OD, so you should be
able to fit that many turns on the toroid. If you want more XL, stack two
(or more) toroids.

Bryan WA7PRC