A time delay can be modeled as the exponential transfer function : e(-sTd) as seen HERE . Therefore the slope of the phase gives us the time delay.
The transfer function of RF multiplexer in rack 1Y1 (NI PXI-2547) was fit to an ideal delay function e(-sTd) , with Td = 59 ns.
The plots shows the actual data, fit data and data after correction using the ideal model stated above.
Delay the RF Multiplexer is approximately 59 ns. This value can be used to correct the phase in measurements of transimpedance for each PD by dividing out the ideal transfer function for time delay.