Trans-hybrid loss is the loss or isolation between the transmit and receive ports of a two-wire to four-wire hybrid. It is directly dependent upon signal cancellation accomplished by defining the line impedance and mirroring it with a balance impedance.

The inherent quality of a two-transformer hybrid can be specified by testing trans-hybrid loss with the two-wire line and balance network impedance set to be exactly equal. Under these conditions, typical trans-hybrid losses could exceed 50 dB* under controlled lab conditions. See Figure 1.

Trans-hybrid Loss of a single transformer hybrid is shown in Figure 2. For optimum isolation between the transmit and the receive ports the value of the balance resistor, R BALANCE, will equal the Z_L impedance that is reflected onto one side of the tapped winding.

Under these conditions, typical trans-hybrid loss may be as good as 20 to 30 dB* over the voice band for a single transformer hybrid.

* For ease of measurement, Wurth Electronics Midcom usually omits consideration of losses to or from the 2-wire line when specifying trans-hybrid loss.