Rf fiber optics
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RF fiber optics. Analog RF transmission with mechanically stressed fibers. Introduction. Advantages of fiber links: Bandwidth depends mainly on the electrical components Very long distances can be achieved Current installation in the Effelsberg telescope:

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Rf fiber optics

RF fiber optics

Analog RF transmission with mechanically stressed fibers


Introduction
Introduction

  • Advantages of fiber links:

    • Bandwidth depends mainly on the electrical components

    • Very long distances can be achieved

  • Current installation in the Effelsberg telescope:

    • 400m from primary focus cabin to faraday room

    • Transmission of RF signals through coaxial cables (25 dB/100m @ 1GHz)

    • Max. useable bandwidth < 1 GHz

  • Analog transmission is able to avoid the bandwidth bottleneck


Analog fiber links
Analog fiber links

  • Miteq SCM Series 0.1 – 18 GHz

  • Miteq MDD Series 0.1 – 11 GHz

  • 9/125 single mode fiber with FC/APC connectors

  • Laser is modulated directly



Results of broadband meas
Results of broadband meas

  • TP_in: nearly constant

  • TP_out: -0,47 – 0,25 dB


Vna measurements
VNA Measurements

  • Build up at the lab bench

  • No loop

  • Miteq SCM Transmitter (18 GHz BW)

  • Miteq SCM Receiver (18 GHz BW)

  • Miteq MDD Transmitter (11 GHz BW)

  • Miteq MDD Receiver (11 GHz BW)

  • 100m 9/125 SM fiber

  • 2m 9/125 SM fiber







Summary
Summary

  • MDD (11 GHz) Receiver: ∆A = 0.22 dB

  • SCC (18 GHz) Receiver: ∆A = 0.78 dB

  • Transmitter has no influence

  • Same measurements with 2m fiber instead of 100m:no change  Fiber length has no influence

  • Measurments with the fiber installed in the telescope are compareable with those in the lab although the fiber is different  Fiber type has no influence


Conclusion
Conclusion

  • Changes in insertion loss:Effect seems to depend on birefrigence caused by mechanical force applied to the fiber. Together with a polarization sensitivity of the photodiode this can cause the difference in insertion loss.

  • Changes in frequency response:Still an open question; Has to be investigated further



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