How can I measure/determine the step up for a helical resonator?

Discussion in 'General Electronics Chat' started by Matjelo Naleli, May 28, 2016.

  1. Matjelo Naleli

    Thread Starter Member

    Oct 7, 2015
    I build a helical resonator for ion trapping application. When loaded with an ion trap (capacitive load) the resonance frequency is 15 MHz.

    The Measurement Problem

    If I measure the output directly from the output terminals of the resonator, the dynamics change and resonance frequency shifts from 15 MHz down to about 9 MHz. I thought it's probably because the measurement device (scope + cables) loads the resonator..

    Attempted Solution

    So to prevent this I build a one-turn coil (acting as a probe) that couples inductively to the output of the resonator.. I now take measurements on this probe.. The idea is to measure the input and output voltages for various frequencies and produce a Bode diagram and deduce the transfer function for the helical resonator..

    Step Up from Probe & Resonator Output

    The problem I face at the moment is how to determine the voltage step up from the probe to the helical resonator output.. This is necessary so that when I see say 5 V on the probe then I just need to multiply it by a step up gain to know what the voltage is at the resonator output at 15 MHz operating point..

    To determine this I have to measure the output voltage of the resonator directly at its output (thus messing up the dynamics) and at the same time measure the probe voltage.. At the operating frequency (15 MHz) the step up that I get is very different from the step obtained at a new resonance (9 MHz)..

    Is any of these step up gains more valid than the other or are they both invalid?

    Any suggestions on how I can carry out the measurement of the step up more accurately for 15 MHz operating point?

    Someone suggested a Network Analyser but I don't have it.