Circuit changes (Updated Schematic)

I made the following changes to SN009:

• R15 -> 10k Ohms for increasing Test Input Power.
• R1   ->  226 Ohms
• R2   ->  25 Ohms (Two 50 Ohm resistors stacked in parallel)
• Added Ln, 2.2 uH fixed inductor.
• Added Cn 0.5-1.5 pF Trim Tunable Capactior.
• Ln and Cn are in series such that Ln + Cn is parallel to R1.
• Rewired the 5V line from one end of C3 to one end of C14 (U8-14) with yellow 20 AWG single core wire.

Updated Photo

Measurements

• I used the setup in 40m to take light transfer function of the modified SN009.
• Method described in CTN:2247 was used.

Inference

• It turns out, however, that the placement of "active" notch didn't help at all. Infact, the ratio between peak and notch went from 30 to 20 :(
• I needed to reduce the values of R1 and R2 to ensure the notch doesn't effect the peak transimpedance much.
• During the tuning, I found that as I turned the screw on the capacitor, the transimpedance will just cycle through phases of low and high impedance. I dont' think I ever saw a very clear notch because of the new changes.
• I also tweaked the passive notch slightly to bring it closer to 72 MHz.
• I'll think more about what has happened and will try another pair of inductor and capacitor.

Data