Built a 40M center-fed dipole using 14 AWG THHN wire, calculated at 66.5 feet total using the 468 formula. When calculating the dipole length, 468 divided by 7.150 gives about 32.5 ft per side. Installed at 35 feet with 1:1 current balun and RG-213 feedline.

Issue: SWR shows 1.5:1 at 7.150 MHz but jumps to 2.8:1 at 7.000 MHz and 3.2:1 at 7.300 MHz. Tried trimming 6 inches from each end but didn't improve band edge performance. Any thoughts on what's causing the narrow bandwidth? Should I consider different wire gauge or balun placement?

The gauge of wire makes a little bit of difference in the bandwidth you get, but the difference between like 14 gauge and 16 gauge is really not significant. Your narrow bandwidth suggests the antenna is working but may need height adjustment. Try raising it to 50+ feet if possible - dipoles need clearance for optimal performance.

Check your balun placement and ground connections. A current balun gives you extra protection from getting RF on your coax, but if it's saturating or poorly grounded, it can affect bandwidth. Also verify your coax isn't contributing to the issue - measure SWR right at the balun terminals.

After raising, lowering, and clipping each half of the antenna five times, you can achieve excellent SWR of <2 across the entire band. The height really matters for dipole bandwidth. Consider adding an antenna tuner if you need full band coverage - it's easier than chasing perfect SWR across 300 kHz.