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Preliminary Results of the VLBI2010 Subgroup 'RF/IF, Antenna, Frequency &Time'

Preliminary Results of the VLBI2010 Subgroup 'RF/IF, Antenna, Frequency &Time'. Hayo Hase, BKG Brian Corey, MIT Yasuhiro Koyama, CRL Dave Shaffer, Radiometrics Inc. Bill Petrachenko, NRCan Wolfgang Schlüter, BKG. Goals.

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Preliminary Results of the VLBI2010 Subgroup 'RF/IF, Antenna, Frequency &Time'

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  1. Preliminary Results of the VLBI2010 Subgroup 'RF/IF, Antenna, Frequency &Time' Hayo Hase, BKG Brian Corey, MIT Yasuhiro Koyama, CRL Dave Shaffer, Radiometrics Inc. Bill Petrachenko, NRCan Wolfgang Schlüter, BKG

  2. Goals Charter for IVS-WG3 “VLBI2010“ requests 'highest precision geodetic and astrometric results'. VLBI2010 design goals: • Space domain: 1 mm • Time domain: 3 ps

  3. Limits • Atmosphere: turbulent, chaotic, time variable atmospheric delay • RFI: reduce SNR or wipe out quasar's noise • Instrumentation • Antenna: mechanical structure, dish surface • HF-components: feed, amplifiers, mixers, oscillators • Samplers: sample rate • Data buffering: max. recording/output bandwidth • Reference oscillator: Allan variance

  4. Atmosphere • Troposphere.  Water vapour radiometry with better directivity on targeting axis. • Ionosphere.  RF below 100GHz must be dual-band.

  5. RFI • Avoidence of polluted bands.  Give up and replace S-band. Candidates: H2O spectral lines at 23.8 GHz and 31.5 GHz! • Mitigation.  Apply technology.

  6. Instrumentation • defines geodetic reference point in space adn time. • characterized by signal-to-noise ratio (SNR) f=0.5 processing factor (1-bit sampling), V=1 visibility unresolved source, Ta antenna temperature, Ts system temperature, 2 Nyquist sample rate,  integration interval

  7. Antenna • geodetic reference marker in space  must allow tie to other space geodetic sensors • wish: more scans per time unit obtained by simultaneous multibeam observations • monolithic antenna cluster • huge phased arrays  delay calibration will decide on the prefered antenna type • (Luneberg sphere would be ideal, if 12m diameter and for frequency range 8-40GHz)

  8. HF-Components • feed: log periodic pyramidal feeds allow wide band reception • amplifier: wide band amplifier allow to observe the entire spectral bandwidth • phase calibration system: diagnostic tool, allows bandwidth synthesis • delay calibration system: at least for distance reference oscillator to receiver local oscillator

  9. Samplers • Sampling with quantization allows RFI mitigation. • High speed samplers allow to sample the entire spectrum at once. • Sampling rates are higher than bit recording rates.  Bandwidth synthesis will be necessary

  10. Bandwidth Synthesis • Sparse in frequency. Narrow bandwidth channels with own BBC samplers. Sensitive to RFI. (Mk3/4/5) • Sparse in time. Burst mode observations. Robust agains RFI when using the full bandwidth. (Pulsar observations) • Frequency switching. Cycles through the observed bandwidth by changing the BBC-LO frequency. Robust against RFI. Less BBC. (S2)  Ideally some BBC channels with frequency switching capabilities.

  11. Data Buffering • Sampling at front end allows data recording or interfacing to optical networks at front end. • (see other subgroup)

  12. Frequency Standards • Better apriori clock synchronisation will constrain VLBI data better to time scale.  GNSS time transfer allow 1ns (Metronome) • Frequency offsets introduce time scale error.  Monitoring of frequency offset must become a standard.  Reference oscillator should have Allan variance better than 10-15 (H-Maser, Mercury ion tramp)

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