Common-mode currents are detrimental to antenna system efficiency, noise or unwanted signal ingress, and/or pattern. Common mode currents:
- in verticals with sparse counterpoise systems negatively impact system efficiency
- in all transmitting antennas can increase local RFI
- in receiving systems increase noise floor
- in all antenna systems can alter antenna pattern, especially in nulls
If common mode currents are significant enough to alter patterns, common mode currents can also transfer unwanted signals and noise into our transmitting antennas when receiving.
Sleeve baluns or snap on baluns are normally used at VHF and higher. They are often not practical at HF.