My mistake. SR RX II input impedance is actually close to 50 ohm.
Thanks to all who have been contributing to this discussion.
I finally figured out why my measurement of the input impedance of the SoftRock Ensemble II differed drastically from what the design would lead one to expect.
Thanks to Warren's suggestion of using a 'scope together with the MFJ 259B, I saw that the 259's output level was 1.2V peak. This exceeds the threshold voltage of the back to back diodes that I had installed on the SR input as a protection against overload. Thus, the MFJ 259B was indicating a low impedance because it was driving the diodes into conduction.
I tacked together an attenuator so that the input voltage was less than .5 Volt and then put a 56 ohm resistor in series. The voltage on the Rx side was just a little less than half that on the high side of the 56 ohm resistor. Thus, the impedance of the Rx input is close to 50 ohm, as expected.
Sorry for the confusion guys.
Now that input mismatch as a possible source for the limited "sensitivity" or noise figure has been eliminated, I can focus on the other issues being discussed. Back later ...
Roger
