End fed half wave antennas

The problem with end fed half waves is they are a high impedance at the ends. This is often outside the range that can be tuned with auto-ATUs in many modern rigs that tune out mismatches to about 3:1 VSWR. The common solution is to add a matching transformer so the auto-ATU can cope. There are several ideas around.

See https://vk3il.net/projects-antenna/efhw-matching-unit/