Next test of EFHW Matchbox

I received the type 2 toroids and started to play with them as before by wiring up the parts and testing with the Mini60 Antenna analyzer. This time I tried 24 turns of #22 magnet wire with a 3 turn secondary. I just could not get a match unless I had 5 or 6 turns on the secondary. The frequency was also way off. This didn’t make much sense. So attacking these issues one at a time, I came up with some fixes. First the frequency was off because of the stray capacitance in the leads I was using to hook up things temporarily. I shortened the leads and started getting better results. As for the matching problem, I first put together a spreadsheet that calculated the amount of inductance for various turns on the T92-2 toroid. Then I added some columns that calculated the frequency range of the capacitor I was using. With this data I can find which winding combinations would give me the tuning range I needed. Then I added columns to calculate the turns ratio and the fixed resistor needed to tune to 50 Ohms impedance. I am attaching this spreadsheet but it is not pretty. It tells me that I can ideally use 18 turns of primary with either 2 or 3 turns of secondary for a match. At 2 turns I need a 4k resistor to tune to 50 ohms. With 3 turns I need 1.8K Ohms to tune.This should let me use the match box to tune 40m through 10m. I’ll provide some plots as I get the matchbox built into its case.

EFHW Matchbox


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