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TDO isolation to reduce frequency noise . Brian C. Chapler Department of Physics, San Diego State University REU Florida State University National High Magnetic Field Laboratory. Main points. Review tunnel diode oscillators (TDO) Uses of TDO Motivation Noise reduction Results

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Tdo isolation to reduce frequency noise

TDO isolation to reduce frequency noise

Brian C. Chapler

Department of Physics, San Diego State University

REU Florida State University

National High Magnetic Field Laboratory


Main points
Main points

  • Review tunnel diode oscillators (TDO)

  • Uses of TDO

  • Motivation

  • Noise reduction

  • Results

  • Conclusions


Lc resonance
LC resonance

Any changes in the inductance of the coil due to the sample will be recorded by the change in frequency


The tunnel diode
The tunnel diode

  • Tunnel diode has region of negative resistance

  • By biasing the diode to be in this region, the diode will drive the circuit at the resonant frequency


Conductivity in metals
Conductivity in metals

Changing the effective area of the coil changes the inductance, which gives a change in resonant frequency


Penetration depth in superconductors
Penetration depth in superconductors

  • Magnetic field inside a superconductor,

    where l is the penetration depth

  • Changing the effective area of the coil leads to a change in resonant frequency


Magnetic susceptibility in insulators
Magnetic susceptibility in insulators

  • Changes in the magnetic susceptibility of a material changes the inductance, which changes the resonant frequency


Motivation
Motivation

  • Need to be able to take data sweeping with temperature in constant magnetic field

  • When temperature is varied, noise becomes a problem


Noise reduction
Noise reduction

  • Experimental apparatus very sensitive

  • Thermal exchange causing hydrodynamic flow disturbs coil

  • Vibration in coil changes the inductance/capacitance of the coil

  • Fluid flow causes temperature fluctuations changing inductance


Isolation chamber
Isolation chamber

  • Coil will be held in leak tight seal

  • Isolating chamber reduces possible temperature oscillations and mechanical vibrations of the coil

  • Size limited by dimensions of probe




Conclusions
Conclusions

  • Isolating the coil showed no significant reduction in noise level at room temperature

  • In liquid nitrogen a huge decrease in noise is observed when the chamber is used

  • Noise is largely dependant on fluid flow around TDO circuit

  • Isolation chamber is effective in reducing noise due to this fluid flow


Acknowledgements
Acknowledgements

  • CIRL

  • Victor Correa

  • Catalin Martin

  • NHMFL

  • NSF

  • Kenny Purcell

  • Stan Tozer


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