Tested EFHW Matchbox components – Fail!

I started to put the EFHW antenna matchbox components together today. I wound 24 turns of insulated #22 wire on a FT140-43 toroid. I measured the inductance and instantly knew I was in trouble…520uH! That was way too much. I will need to order some powdered iron cores to get the inductance down to where my capacitor can tune it. I found a decent source at Alltronics and ordered a variety to try out. Also ordered some #22 magnet wire so that I can try and wind a smaller diameter core.

Update 7/25/2016: Amidon has a bunch of good table and charts useful for designing with toroids. As I indicated above the FT-140-43 toroid is great for a balun but because of its high permeability resulted in over 500uH in inductance… So I have three sizes on order of powered iron Type 2 cores. 24 turns on the T80-2 core results in 3.1uH while the T94-2 results in 4.8uH. Using an LC calculator online my frequency range using the capacitor I have on hand and the T80-2 core is 5Mhz to 29Mhz.  Should let me develop a EFHW antenna for 40m through 1om. Just have to wait for the parts now.


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