I’ve had good luck with an endfed antenna on 20 and 30 meters. Depending on available trees/supports I can arrange this antenna as an inverted vee, a sloper or a horizontal 1/2 wave. It functions an endfed zepp on 20 meters consisting of a 1/2 wave 20 meter wire (33′ 3″ long) endfed with a 1/4 wave x velocity factor of twin lead (14′ 3″ long). By disconnecting the grounded side of the twin lead it becomes an endfed antenna on 30 approximating 1/2 wave long. By being a 1/2 wave long I avoid the need for an extensive ground system. If RF in the “shack” is a problem, a connection to a convenient ground clears it up.
This antenna behaves very differently on 20 vs 30 meters. On 20 the twin line transforms the hign impedance of the endfed 1/2 wave 20 meter wire into a low impedance that is easily handled by many QRP rigs. On 30 meters this impedance transformation does not happen. The rig is connected directly to the high impedance feed point of the 30 meter antenna. In both cases, though, the K1 built-in automatic antenna tuner allows the rig to work fine.
The endfed 20/30 meter antenna “wired” for 20 meters. On 30 meters disconnect the short black wire from the binding post. If required, a ground may be connected to the black binding post.
A project by W0VLZ