Methods of transfer of ultra-stable frequencies to radio telescope А.Tsaruk, А. Vytnov, D. Ivanov Institute of Applied Astronomy of Russian Academy of Sciences 3rd International VLBI Technology Workshop 10 - 13 November 2014 Groningen/Dwingeloo, the Netherlands

Overview Transfer methods of reference frequencies Components Unit forming the reference frequency Results

Introduction Estimated frequency instability which must be provided for coherence losses less than 1% on 1 hour integration time IAA Transactions, 2006, V.15, P. 140-155 [Trudy IAA RAS(in russian)]

Transfer methods of reference frequency 100MHz to radio telescope Transmission of the 100 MHz signal via RF cable with amplification. Transmission of the 5 MHz signal via RF cable with amplification and multiplication. Modulation of the optical signal by radio frequency 100 MHz and its transmission via fiber optic cable with demodulation on the radio telescope.

Transfer methods of reference frequency 100MHz to the radiotelescope

Components LOW NOISE FREQUENCY MULTIPLIERS x10 x2 Ultra-Low Phase Noise: -143 dBc/Hz @ 1 Hz  -170 dBc/Hz @ 1 kHz  -176 dBc/Hz @ 100 kHz AMPLIFIERS DISTRIBUTION AMPLIFIER FIXED GAIN Low phase noise:  -158 dBc/Hz @ 10 Hz  -172 dBc/Hz @ 10 kHz

Components Laser module Optical receiver Optical isolator Connector Type FC/APC Wavelength 1.55 μm Frequency Range 0.1-7000 MHz Maximum optical attenuation -25 dB Relative Intensity Noise -140 dB/Hz Connector Type FC/APC Wavelength 1.31-1.55 μm Frequency response irregularity ±3  dB Frequency Range 0.1-7000 МHz Return loss -25 dB Connector Type FC/APC Insertion loss 0.41  dB Isolation 47.5 dB Optical circulator

Reference frequency transmission via fiber optic cable

Cable delay compensation scheme

Unit forming the reference frequency signal Ground part Antenna part

Unit forming the reference frequency signal (antenna part) Supply stabilization Ripple and noise < 3mV Temperature stabilization The internal temperature +35˚С at an external temperature of +5˚С...+40˚С

Results

Conclusion The device is developed for the reference signal transmission to the radio telescope, allowing to transmit the signal of the reference frequency by optical and RF cable. Introduced frequency instability in both methods of transfer reference frequency avoids the coherence loses greater than 1% on time interval of 1 hour. At the moment there is an installation of the designed formation block of the reference frequency on the radio telescopes RT-13 produced by IAA RAS. Their future operation will show efficiency of the proposed methods for transmitting reference frequency on the radio telescope in real conditions.

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