ToddDubya
NES Member
Well, I just spent the entire morning until now working on a 1:1 choke balun with banana jack terminals to connect a dipole. I used an FT240-31 toroid and magnet wire, 12 turns of each pair on either side of the toroid, effectively two sets of inputs/outputs shorted together. I wired each side such that the left and right side are mirror images of each other.
I probably should have checked the SWR along the way, but I at least made sure the correct wires were shorted and the incorrect wires weren't shorted. 0 ohms from inputs to respective outputs.
To test, I put a 50 ohm Dale power resistor across the terminals and got basically a 10:1 SWR from 3-50MHz with two narrow resonant points. Okay, that resistor is probably reactive as hell.
Next I tried two 100 ohm carbon resistors in parallel across the output terminals and ran a scan on that. It's better, but still terrible.
I expected to see close to 1:1 across the board. Instead it starts out around 1KHz at 50 +j0, but as frequency climbs the resistance climbs and it becomes more reactive. Here's the Smith chart from 3.5MHz to 30MHz.
If we ever have decent weather again I can try putting up one of my dipoles and see how that does.
In the meantime, what the hell? Anybody know what I'm doing wrong here? I'm hoping it's just my measurement technique that is causing it, but I didn't expect carbon resistors to be so reactive.
I probably should have checked the SWR along the way, but I at least made sure the correct wires were shorted and the incorrect wires weren't shorted. 0 ohms from inputs to respective outputs.
To test, I put a 50 ohm Dale power resistor across the terminals and got basically a 10:1 SWR from 3-50MHz with two narrow resonant points. Okay, that resistor is probably reactive as hell.
Next I tried two 100 ohm carbon resistors in parallel across the output terminals and ran a scan on that. It's better, but still terrible.
I expected to see close to 1:1 across the board. Instead it starts out around 1KHz at 50 +j0, but as frequency climbs the resistance climbs and it becomes more reactive. Here's the Smith chart from 3.5MHz to 30MHz.
If we ever have decent weather again I can try putting up one of my dipoles and see how that does.
In the meantime, what the hell? Anybody know what I'm doing wrong here? I'm hoping it's just my measurement technique that is causing it, but I didn't expect carbon resistors to be so reactive.