Find the radiator and matching-stub lengths for a J-pole antenna, the classic no-radials VHF/UHF vertical, at any frequency.
A J-pole is a half-wave radiator fed by a quarter-wave matching stub, so it needs no radials. The long element is three quarters of a wavelength, the short stub is a quarter, both with a 0.95 velocity factor. The feed taps onto the stub an inch or two up; slide it for lowest SWR.
The long radiator is three quarters of a wavelength and the short matching stub is a quarter, each with a 0.95 velocity factor. For 2m at 146 MHz that is about 57.6 inches long and 19.2 inches short, the classic J-pole numbers.
The quarter-wave stub is an impedance-matching section that transforms the end-fed half-wave radiator down to 50 ohms, so the antenna is self-contained and end-fed. That makes it a favourite for masts and portable VHF/UHF use.
The feed taps onto the two stub conductors an inch or two above the bottom short. Start low and slide the tap up for the lowest SWR; the exact point depends on tubing size and spacing.