There are many types of common mode chokes available, HF Kits opts for a common mode choke with bifilar windings for optimal filtering.The main reason for using a common mode choke is to ensure that the coax cable’s shield does not become part of the antenna system and will radiate unintentionally. This has all sorts of nasty effects, think of: interference issues, disrupted radiation pattern of the antenna and a higher noise level. This last point is because not only does the coax cable’s shield radiate when you transmit, but the shield also works as a receiving antenna. Because the coax cable often makes a considerable trip within the house, close to interference sources (mains, PLC etc…) It is useful to eliminate these sources of interference. Any way, Good reason to use a common mode choke.I'm a product description. I'm a great place to add more details about your product such as sizing, material, care instructions and cleaning instructions.