by Chris P » Wed Nov 20, 2019 6:20 pm
adding a further length of different diameter cable to an HF longwire will not make any difference but the frequency of resonance will change due to the additional length.
make sure you have a good connection and make it watertight as rain will corrode the joint in time. Doubling up on the added section will not strengthen the antenna much as the additional weight will increase the load on the whole length
Regards Chris aka G8FFF nipper or tazmin88