Does DiSEqC require a DC bias?
It uses 22kHz burst communication in this interface rev, not DC control.

REF To permit slave devices to communicate back to the master, it is necessary to make more specific recommendations for the operating impedances of the bus than is required for a simple 22 kHz continuous tone signalling. In addition, it is advantageous to be able to accept a wide range of DC operating voltages during the DiSEqC introductory phase, to permit compatible and/or hybrid operation with the present signalling methods.

The recommendations for operation of the DiSEqC Bus are: The long-term recommendation for the DC Supply voltage is 12 ± 1 volts, but during the introductory phase, voltages up to 20 volts should be tolerated by peripheral devices (i.e. not suffer catastrophic failures). For the short term, some manufacturers may choose to retain compatibility with 13/18 volt signalling levels, and this facility is supported in the first versions of the DiSEqC Slave integrated circuit.

It is recommended that Tuner-receiver/IRDs should support a DC Supply
current drain of up to 500 mA for peripheral devices powered by the Bus.   The nominal 22 kHz signalling amplitude is 650 mV (±250 mV) peak-peak.
To accommodate tolerances and voltage drop in the cable, the detector should respond to amplitudes down to approximately 300 mV (±100 mV). The maximum recommended amplitude to be applied to the bus is 1 volt peak to peak