[amsat-bb] Please help me design a polarity switcher...

[Elan Portnoy]

I have both vertical and horizontal elements of my 70cm yagi coming into the shack via separate runs of LM400. They meet in a box with bits of coax for matching and phasing before going to the radio. 

I would like to add a relay to make polarity changes quick and easy. Do I need to use a specific type of relay or will a garden variety DPDT from Radio Shack be sufficient?

Thanks,
Elan WB2IOL