[amsat-bb] Making a phasing line for 70cm polarity switch

I would like to know how to make a 1/2 wave phasing line for my Gulf Alpha 70cm polarity switch. I've lost the original one while moving.

I understand that using a SWR meter is how it's done but I'm not sure of the details. Is there a better way?

I'd appreciate some help.

Bob WL7CQX