I recently modified the 2 elements on 80 meter to be switchble between CW and SSB band side.

The boom also has been substituted.with a stronger one.

The swicth  box has been built using a electrical plasting box , suitable for external application, bought in a electrical warehouse.

Circuit description

A coil has been added close to the balun (for the radiator element) and a relays adds or excludes it to the antenna circuit. You need a coil for each dipole leg.

Finally I set-up four coils, inserted into two boxes, one for radiator and  the other for fhe reflector element.

Box construction

The 2 boxes used has been bought in a electrical warehouse; they are plastic ones    for external use and they are large enough to guest the two coils.

Each coils has been realized with enameled full wire 4mm OD; I was able to find it in a small factory which rebuilds electrical engines.

Coils measure are 100mm OD and 6 full turns was needed for my application.

The switching has been realized using four vacuum relays,  Jennings RF5A-26S 12 amp. 7.5 kv. (See Surplus Sales) or MAX-GAIN systems.

Tuning method

Tuning is quite long to achieve; you need to easily put up and down the at least one element to verify that the switch box is able to guarantee to you enough the band desired (typically 250-300 hz as 3.500 for cw and 3.800 for SSB operation)

After that you have identified the theoretical dimension of the coil, you need to find by proof the right length of the coils.

 In my case I wanted to work at  3.500 and 3.800.

You don't need to put dipole as high as final working height; you need to see that the applying power to the relays and monitoring the SWR with a tuning instrument (I use the MFJ 259), you can read, between the lower and the upper frequency, 300 hz, even if it is not exactly the final one (could be lower, could be upper).