[Michael R., Volker Q.]
After installing the new EOM and measuring the PM sidebands, see previous entry, we measured the RFAM on the core modulation frequencies 9.1MHz, 45.5MHz and 24.1MHz. All frequencies were driven with 10Vpp. The measurement was performed using a LZH aLIGO PSL locking PD (D1002163) mounted at the position of IO_AB_PD1.
The AC path of this diode has a 4x amplification with respect to the DC path and 50 ohm output impedance. The DC path also has 50 ohm output impedance.
The DC value was measured with a TDS 2024 into high impedance, the AC output was measured with an Agilent 4395a into 50 ohm. (Note, this gives another factor of 2 for the DC value.)
The RFAM was calculated using this formula RFAM = (V_AC/4) / (V_DC/2) accounting for AC amplification and DC path impedance. V_AC denotes the Vrms as measured with the spectrum analyzer and V_DC the voltage read from the oscilloscope. The PM value below is the modulation index as measured previously. As a sanity check the V_AC measurements were done with the dBv, dBm and Volt settings of the spectrum analyzer to confirm that Vrms is displayed. The following table shows the measurements:
| DC value in mV | PM | 45.5 ampl. (dBV) | 45.5 ampl. (dBm) | 45.5 ampl. (uV) | RFAM | Frequency | RFAM/PM | ||
| 930 | 0.31 | -79.8 | -66.8 | 103 | |||||
| 1.02E-04 | 1.02E-04 | 1.03E-04 | Vrms | 5.50158E-05 | 45.5 MHz | 1.77E-04 | |||
| 9.1 ampl. (dBV) | 9.1 ampl. (dBm) | 9.1 ampl. (uV) | |||||||
| 0.39 | -75.4 | -62.4 | 172 | ||||||
| 1.70E-04 | 1.70E-04 | 1.72E-04 | Vrms | 9.13034E-05 | 9.1 MHz | 2.34E-04 | |||
| 24.1 ampl. (dBV) | 24.1 ampl. (dBm) | 24.1 ampl. (uV) | |||||||
| 0.14 | -84.6 | -71.5 | 61 | ||||||
| 5.89E-05 | 5.95E-05 | 6.10E-05 | Vrms | 3.16583E-05 | 24.1MHz | 2.26E-04 |
The Agilent 4395a was set to BW = 3kHz.