Ian Jackson wrote:
Cecil Moore writes

| |
| coil coil |
+-------------/////FP/////-------------+
| || |
| || |

Connect a 80m quarterwave S/C stub (preferably twin feeder) across both
coils (ie from the outer end to the outer end). That will leave the
coils O/C on 80m and S/C the coils on 40m.

A somewhat weird looking modification for a center-fed
vertical antenna. I suppose the two stubs could double
as guy wires. I might be tempted to accomplish the switching
with a large open frame relay or two.
--
73, Cecil http://www.w5dxp.com