Oct 20, 2018 · Putting a common-mode choke inline will prevent RF on the outside of the coax getting back into the shack. According to some sources (ref.1), an end-fed half-wave antenna needs a 0.05 lambda counterpoise to work correctly. Feed Line Choke Each end fed antenna needs a feed line choke at the radio end of the coax to stop the antenna common mode current (on the coax braid) from getting into the radio when transmitting and also to stop RFI common mode noise when receiving. The simplest, most cost effective choke is a ferrite ring (F240 size) installed as shown in the picture (at the transceiver end of the coax) Add Although not necessary, a 1:1 isolation/choke balun (models, 1110, 1113, 1115 etc.) at the transmitter end of feedline will stop RF from entering your equipment and reduce receiver noise caused by common mode currents. The par antennas are sleeve dipoles. Not really end fed. They use skin effect and an isolating choke to stop signal from travelling further down the wire. All antennas need a counterpoise. Try this if you have a mono band ht. Cut a wire about 1/4 wave long on the band it works on, attach somekinda way to ground side of antenna jack.