You may want to feed your balun in common mode just as the TRX bench guy has done with 25 ohm resistors. Then, you will discover how it performs.

Fascinating, broadly similar to my results, I was considering sleeving the wires to try to reduce turn to turn capacitance 73

@arcanestudio

2 жыл бұрын

The windings on the balun are controlled impedance transmission lines on both sides of the core. The transmission line impedance should be 100 ohms for optimum performance. In order to make this transmission line, DG0SA has chosen #18 AWG PTFE wire. The wire is either solid silver or silver plated. Sadly, the DG0SA website says that he has passed away, but the site is still available.

@arcanestudio

2 жыл бұрын

If you were to sleeve the wire, you would alter the transmission line impedance which has to be 100 ohms.

@g0fvt

2 жыл бұрын

@@arcanestudio I meant an overall sleeve with each pair of conductors in it. As you say PTFE insulated wire is silver plated, as the coating attacks copper. Sleeving the "pairs" would not change the transmission line impedance.

@arcanestudio

2 жыл бұрын

​@@g0fvt I am sorry to have misunderstood your original intent. From what I have read, the windings should be wound as tightly as possible on the core - without air gaps. Controlling the transmission line impedance appears to be the most important parameter for ensuring success - cheers, K1FQL

@g0fvt

2 жыл бұрын

@@arcanestudio no problem, from my own experience with them the common mode impedance suffers when they have too many turns. I do not know whether this is down to the capacitance. Certainly effective common mode chokes are a powerful weapon when RFI is an issue. 73

I've not understood the need to put the resistors in series with the test circuit. How would this affect the actual amount of attenuation provided by the windings on the toroid, or more importantly, the measurement of same?

how much power one ft240-43 can withstand in this configuration