RF Combiners (or Splitters)

One of the tangled things for which there seems to nothing very clear on the web is about combiners. specifically a way to combine two RF signals with zero phase shift and equal gain on each channel.

These are typically used in an SDR to combine to two outputs of the RF mixers which have 0/90 phase RF and 0/90 AF inputs.  So here is what I have found, three solutions:

The single transformer solution, 50R in 25R out

Port A = 50R

Port B = 50R

Port S = 25R

Rint = A+B = 100R

Obviously this does not have both 50R input and output, the two ports on the right are 50R, but the combined one on the left is 25R.

The two transformer solution with matching 2:1 to give 50R inputs and output

J2  = J3 = 50R

L1 tap mat 0.7 to give 2;1 ratio, J1 = 50R, tap = 25R. 10:7 turns FT37-43

L2 Bifilar 10t+10t FT37-43

R = J2 + J3 = 100R

C for HF compensation.

A single transformer with an impedance ratio of 1.4:1, to give 50R inputs and output

R = 50||50 = 25R (51+51R parallel)

10t / 7t+7t bifilar FT37-43