You're probably thinking of a single transformer hybrid.
simulate this circuit – Schematic created using CircuitLab
The resistor should be half the system impedance, so 25Ω for a 50Ω system. I'll assume a 50Ω system for the rest of the description.
P1 sees the loads on P2 and P3 in series. If we assume all loads are 50Ω, P2 and P3 in series are 100Ω. Setting the turns ratio with 10 on the P1 side and 14 with a center tap on the other side (with a center tap) makes makes a 1:2 step-down transformer (because $10^2 / 14^2 \approx 1/2$). Thus, P1 sees a matched 50Ω.
P2 sees the matched load at P1 but through a 1:2 step-down transformer (25Ω) in series with another (25Ω) to see a net 50Ω matched load. Thus, signal from P2 is equally divided between being across P1 and the resistor. P3 sees this voltage across the resistor, but it also sees the voltage across P1 in antiphase. These two cancel such that a signal applied at P2 does not appear at P3.
The cost of this isolation is a loss of half the signal power from P2 or P3. For a receive application this may be negligible provided the receiver noise floor is significantly below the (additionally attenuated) received RF noise floor.
Absent a datasheet, I usually look at torroids.info for data, or find a solution empirically.