Circuit changes (Updated Schematic)

I made the following changes to SN009:

• R15 -> 10k Ohms.
• R1   ->  100 Ohms
• R2   ->  10 Ohms
• Added Ln, 220 nH fixed inductor. (Coilcraft 1206CS-221X_L_)
• Added Cn 4.5-50 pF Trim Tunable Capactior (GKY50086).
• Ln and Cn are in series such that Ln + Cn is parallel to R1.

Updated Photo

Measurements

• I used the setup in 40m to take light transfer function of the modified SN010.
• Method described in CTN:2247 was used.

Inference

• The ratio of resonance peak at 1-Omega (37 MHz) to 2-Omega (74 MHz) has been improved from about 20 to about 120.
• This is less improvement than what we saw on the SN009 case.
• Also, the measurement through test port and using lasers is not matching up. This could mean that my estimation of DC transimpedance is wrong.
• In the last plot, I tried multiplying the measurements of the result by a factor of 3.56 and it makes the transimpedance measurements match with test port measurements.
• This shows there is a factoring error in my estimation of dc transimpedance or maybe the whole thing is damped down when light falls on the photodiode instead of test signal.
• Also, there is a significant oscillation peak at around 200 MHz. Maybe that is the reason for the damped overall transimpedance. Working on this next.

Data