Common mode choke Recently I assembled a Common mode choke from HFkits to use with my vertical antenna that, due to space restrictions, do not have radials as counterpoise. This common mode choke should cover the HF band from 3MHz to 30MHz. A common mode choke should prevent the outer conductor from radiate. And it may prevent noise picked up from the outer conductor to reach the radio. This is how the kit after I opened the package.