More 6-meter Dipole Experimentation

I spent much of December of 2025 playing around with alternative feed points and adjusting the resonant frequency with variable capacitors across the feed point.

Autotransformer toroid feed point for the 6-meter dipole, with variable capacitors across both sets of terminals

NanoVNA: SWR of 1.121 @ 55.6 MHz, 45.58+j3.222Ω

Twin coax feed for the 6-meter dipole, with a variable capacitor across the antenna feed point terminals

"Normal" feed for the 6-meter dipole, with a variable capacitor across the terminals

NanoVNA: SWR of 1.21 @ 51.15 MHz, 41.05-j164mΩ

One thing I kept seeing was a strange SWR spike at about 50 MHz, which I still can't explain to this day. Maybe the balcony railing was resonating?

Mix 61 autotransformer toroid feed, with a variable capacitor across the input terminals

NanoVNA showing the SWR spike: 1.944 @ 49.9 MHz, 93.63-j15.6Ω

I also tried a resonant stub to see if that would do anything interesting, but the SWR spike remained.

"Normal" feed for the 6-meter dipole with a parallel stub

Mix 61 autotransformer toroid feed, with a variable capacitor across the input terminals and a parallel stub

NanoVNA: SWR of 1.19 @ 51.5 MHz, 53.71-j8.222Ω

NanoVNA: SWR of 1.043 @ 49.8 MHz, 49.18-j1.909Ω

DD8SF wondered if the autotransformer was hitting resonance, but that occurred at around 69 MHz.

Mix 61 autotransformer toroid with NanoVNA: resonance around 69.4 MHz

While this experimentation didn't really pan out thanks to that weird SWR spike, don't think I'm done with this dipole! There's more experimentation to follow.

#AmateurRadio #HamRadio