Rana, Kiwamu

In order to study why the DRMI seems to lock faster at 1 Watt (see alog 14508), we checked the RF level of REFLAIR_A which is the one we use for acquiring lock of the DRMI.

The RF level at the output of the PD can be as high as -5 dBm and 3 dBm at maximum for 9 and 45 MHz respectively. This may be a bit too high, but certainly not outrageously too high.

(some details)

We hooked up a 300 MHz oscilloscope to the RF mon of the demod boards and checked the RMS value of the RF signals when the DRMI was flashing. Using the trigger on the scope, we captured two incidents where the RF level was high as follows:

• case 1 (triggered by the 45 MHz signal):
  • 9.29 mV rms or -27.6 dBm at 9 MHz
  • 21.8 mV rms or -20.2 dBm at 45 MHz
• case 2 (triggered by the 9 MHz signal):
  • 9.32 mV rms or -27.6 dBm at 9 MHz
  • 8.78 mV rms or -28.1 dBm at 45 MHz

Since the attenuation from the RF input to the RF mon on the demod board is 23 dBm, the real input signals must have been bigger by 23 dB than what we observed on the scope. Therefore the highest signals we expect at the output of the RFPD are -5 dBm and 3 dBm at 9 and 45 MHz respectively.

Note that when the DRMI was locked, there was almost no RF signals. We occasionally saw small signal of about -40 dBm at 45 MHz which we think was some kind of seismic excitation.