User Tuneable 4 Tuning Points Notch Filter Block. This Vision high performance filter is designed to attenuate unwanted 4G mobile phone interference or any other interference, as the unit is tuneable by the installer as required. The OBF4LTE should be inserted into the input of the reception system before any amplifiers, active devices or receivers to exclude interfering signals from the whole network. Where the interfering signals are very strong, additional filtering may be necessary especially where it is received directly onto the coaxial cables / flyleads.