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Message ID: 2376     Entry time: Wed Jul 24 16:14:42 2019
Author: ScottA 
Type: DailyProgress 
Category: RFAM 
Subject: Transfer Function of EOM Driver plus Bias Tee from RF Input to EOM 
  • I have calculated the expected transfer function from the RF input of the EOM Driver (DCC: https://dcc.ligo.org/D1200794-v3) to the direct short connection to the EOM (Graph 3).
  • To do this I took the transfer function calculated in the previous post (Graph 2) which was from the RF input to the RF monitoring port and divided it by a calculated transfer function from the EOM Short to the RF Monitoring port (Graph 1).
  • The gain at 37 MHz seen by the EOM is around 10, in order to get a modulation depth of 0.3 we need a signal with 40 Vpp. This means we need a 4 Vpp input signal to achieve the desired modulation depth. As mentioned in https://nodus.ligo.caltech.edu:8081/CTN/2242 "the frequency source is a preamplified OCXO crystal sources (see PSL:2235, for info and links) that outputs about ... +26 dBm out of the EOM driver SMA."
  • +26 dBm is a voltage of 4.4 volts which is at the required level for the 0.3 modulation depth, so it seems this circuit will perform what we want.

Summary of Results:

  • The transfer function from the RF Input of the EOM Driver to the EOM has a resonant peak around 37 MHz with a max gain of around 10.
  • This gain will be enough to get a 40 Vpp signal which equates to a 0.3 modulation depth. 

Edit Thu Aug 1 16:11:12 2019 ScottA :

4 Vpp is actually 16 dBm, so we need to feed 16 dBm power from OCXO to the EOM. So we'll need ~10dB attenuation but everythign will still work.

Attachment 1: Graphing_TF_BiasTee_7_24_2019_atEOM.zip  200 kB  Uploaded Wed Jul 24 17:17:17 2019
Attachment 2: Transfer_at_EOM.pdf  57 kB  Uploaded Wed Jul 24 17:17:44 2019  | Hide | Hide all
Transfer_at_EOM.pdf Transfer_at_EOM.pdf Transfer_at_EOM.pdf
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