I'm driving the input of the delay line box with 10 dBm from Marconi's RF output.

• First, tuned the Marconi carrier frequency to 112.8 MHz to null the output of the delay line mixer (after DC coupled, G=1, dynamic range mode, SR560 buffer with 1 kHz, 6 dBm/oct lowpass).
• Next, frequency modulating the RF carrier at 314.14 Hz with 800 kHz deviation from the Marconi. The output of the delay line box is an 16 mVpp sine wave, see attachment 1
• I checked out the noise spectrum of the Marconi buffered through both the DC coupled SR560 above, and separately an AC-coupled, G=100, low noise mode SR560 with 10 kHz, 6 dBm/oct lowpass
  • On the Moku, the spectra look reasonable. The G=1 and G=100 peaks at 314 Hz differ by 40 dB, as expected. Attachment 2.
  • Feeding the signal to our ADC has some issues. Not sure what's going wrong (ground loops? hot swapped AA-ADC cable?), but any signal I plug in to the ADC results in the periodic noise in attachment 3 on not only the signal-carrying channel but also the adjacent channels. The discontinuities are larger than the G=1 buffered signal, though not as large at the G=100 buffered signal.
    • I'm using the PSOMA channels, so the names are innaccurate. In attachment 3, the DC-coupled signal is in SLD_PDH_CTL, while the AC-coupled signal is in SLD_PDH_SIG
    • The noise is at about 120 Hz, which suggests some power line issue. Measuring only the AC-coupled SR560 in battery powered mode, with no other instruments connected after the buffer, improves but does not eliminate the noise (attachment 4). Also, on battery powered mode, the SR560 constantly overloads; my exact sequence of steps to observe this overload behavior was (1) power off the SR560, (2) unplug the line voltage, (3) power on the SR560.