Building my first Super-J for 2 meters and running into the classic phasing coil tuning issue. According to WB3AYW's spreadsheet calculations for 146 MHz, the phasing coil should be 1.5" diameter with 32 turns, but several sources suggest shorter coils with different spacing work better. The theoretical 0.2 wavelength phasing section translates to about 13.5" electrically, but mechanically wound coils seem to require different physical dimensions. Has anyone actually measured the electrical length of their working phasing coils versus the physical wound dimensions? I'm using #12 AWG solid copper on 1/2" CPVC form.

That spreadsheet gets the ballpark right but real-world capacitance between coil turns changes everything. I ended up with 19 turns at 1.25" spacing on my working 2M Super-J - way off the calculated 32 turns. The key is having an antenna analyzer and tweaking inductance while watching the pattern on a distant repeater.

Don't forget about coil capacitance and wire routing through the form - that changes the electrical length significantly. I measure each coil's inductance with an LC meter before assembly, then adjust spacing to hit the target reactance for the operating frequency rather than relying on turn count alone.

Using 1/2 wave elements you can stack as many as you want, but beyond 15 elements the pattern gets too flat. For a basic 2-element Super-J, I've had good luck with the 1.5" coil spacing mentioned, but always end up trimming the radiator lengths more than expected. The coil interaction with nearby metal really matters.