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Entry  Thu Dec 16 10:46:36 2010, Zach, Electronics, GYRO, EOM circuit 400_ohms.png25_ohms.png
    Reply  Thu Dec 16 13:13:02 2010, Koji, Electronics, GYRO, EOM circuit 
       Reply  Thu Dec 16 19:46:39 2010, Zach, Electronics, GYRO, EOM circuit refl_signal_with_and_without_R.png
Message ID: 1222     Entry time: Thu Dec 16 10:46:36 2010     Reply to this: 1223
Author: Zach 
Type: Electronics 
Category: GYRO 
Subject: EOM circuit 

 I finally asked Frank if I could just borrow the impedance test kit to measure the EOM resonant circuit impedance, as I have been having problems with the voltage transfer function method. I took the measurement and found that the peak impedance was 400 Ω (see first figure below). Pleased by the round number, I figured I could just add another transformer at the input to divide this down to 50 Ω.

The results weren't as nice as I'd like. First, I forgot that while the voltage ratio is in proportion to the turn ratio, the impedance ratio is in proportion to the turn ratio squared. So, for lack of a 1:8 RF transformer in the kit, I took another 1:16 transformer and only bridged across half of the secondary coil, so as to presumably get a turn ratio of 1:8 (though admittedly I wasn't sure about this). This resulted in a surprising peak impedance of around 150 Ω, though I do not have data for this

Knowing that I needed a larger ratio, I decided to just connect across the full secondary coil (so that I now had two cascaded 1:16 transformers). The resulting peak impedance is now 23 Ω (see second figure---note also that I have adjusted the tunable inductors to make the resonant frequency 33 MHz, instead of the 37 MHz it was in the first plot).

Clearly, I need something in between, but I am not sure how to do this without a THIRD transformer, which seems gratuitous. Perhaps I can measure the reflected power and decide if we can deal with it?




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