What is a Bias T?
This is a simple passive device that couples AC and DC power. In this particular instance, it couples RF Power from your radio and DC power onto a single coax cable. A similar circuit is contained in the RF Switch to separate the DC from the RF signal. A substantial effort has gone into selecting and testing the components for the Bias T to ensure there is minimal impact to SWR over the range of HF-6M.
Caveat – Lightning Arresters
Please be aware that most of the Polyphaser lightning suppressors do NOT conduct DC. There is a capacitor inside their device which will block DC. Please consult the ARRL Lightning and EMI handbook for alternatives or relocate the Polyphaser to the antenna coax beyond the RF Switch.