Are you using bare copper wire or wire with an insulating cover copper wire like house wiring? Generally when I build an antenna, I start with the following formula taken from the ARRL Handbook: Length (ft) = (492 x 0.95) / f(MHz), where the f(MHz) is the center frequency of the dipole. Once I know the length, I add a couple of additional feet of wire to each end. From there I get the antenna up in the air to take the first measurements to get a reference starting point. Hopefully, the resonant point will be higher than the center frequency you want for the dipole. If so, then you need to bring the antenna down and cut a couple of inches from each end of the wire. Place the antenna back up in the air and recheck your reading, hopefully, you will see the resonant point move towards your desired center frequency, it may not be much of a change, maybe a few MHz. Time to bring the antenna back down and cut some more off the end, and recheck the SWR and resonant point. As you get closer to your center frequency, start cutting a shorter amount of wire off the end. Instead of 2-4 inches, now only cut 1 to 1/2 inch off. If it turns out you went below your center frequency, you will need to start over with new wire or add wire to your existing antenna.
Good Luck
David S
