I took a 1/2 wave vertical (17 ft tall) made from telescoping aluminum tubing and shortened it to 13 ft to try it on the 18.1 MHz (17m) band. Took out the impedance matching circuit and just hooked up the center of coax to the antenna, braid to two or three radials.

Easy to tune up with a few radials.
Worked stations all over the world with FT8

Here is the Nano VNA trace of both SWR and RETURN LOSS (dB)

de k3eui barry
philly region

Try a third trace and plot RESISTANCE. See how close to 50 ohms you are at the resonance point. The NanoVNA is truly a remarkable device.

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Bernie Murphy, VE3FWF
*Real* radios glow in the dark

I am doing something similar. I have a vertical that was set for the 30m (10.1 mhz) band and made it into a efhw vertical for 17m. I added the 49:1 unun at the bottom. I need to sweep it to see where center freq is and if it is covering any bands higher up. Also I used some old coax so I want to do a tdr on the coax to check if I need to replace it.

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73 de W8NSI Jim
New NanoVNA User, please be patient.
I build my own antennas and need this.