The observation technique as discussed in the previous section was implemented at the University of Tasmania, using the 12m radio telescopes at Hobart (Hb), Katherine (Ke) and Yarragadee (Yg), as well as the 30m at Ceduna (Cd). The UTAS radio telescopes are equipped with standard VLBI backends, data acquisition systems and hydrogen-masers for the clock standards. These antennas are all capable of receiving in the X-band, which includes JUICE’s standard transmission frequency of approximately 8436 MHz.
The 12m antennas’ receivers produce signals in linear polarisations (horizontal and vertical), while the transmitted signal is circularly polarised. The radio frequency received by the radio telescopes is down converted, within the 6-10 GHz sky frequency band, to an intermediate frequency between 0-4 GHz. The local oscillator (LO) for the down-conversion is set to 6.00 GHz. The analogue signal is then sampled with the digital baseband converters 3 (dbbc3) [15]. These data use 2-bits per signal, and can have a variable bandwidth, with 8, 16 or 32 MHz typically used for spacecraft observations. The data is stored to disk for offline processing.
The antennas also feature software defined radio (SDR) and GNU Radio2 to record at a higher number of bits per sample and a lower sampling rate. The design runs in an Ettus X3103 at Hb and in an Ettus N210 at Ke. These record complex or real data using 32-bits per sample with a 1 MHz bandwidth. Additionally, the Ettus can be used to visualise the spacecraft signal in realtime. Fig. 3 shows the schematics of the current design at the Hobart and Katherine 12m antennas, as well as the Ceduna 30m antenna.

[Figure: Figure 3: Diagram of the data recording setup on the Hobart and Katherine 12m antennas (left) and Ceduna 30m (right) [16]. RFoF is Radio Frequency over Fiber.]

Observations are scheduled when JUICE is transmitting, telescope time is available, and the spacecraft is above the horizon at the telescope locations. The JUICE mission operation reports
2 http://www.gnuradio.org/ 3 https://kb.ettus.com/Knowledge_Base contain a schedule of transmission times.

This is used to select an observation time when the spacecraft is communicating with the ESA New Norcia antenna, based in Western Australia, as this provides good elevation overlap with the UTAS antennas.
At least two natural sources were needed for each observation: a fringe finder and a phasereference source. The fringe finder source was ideally a very strong source but could be located anywhere in the visible sky, whilst the phase-reference source was required to be within two degrees of JUICE’s position. JUICE’s predicted right ascension and declination was found using JPL Horizons4, and the Astrogeo VLBI Calibrator search5 was used to find natural radio sources angularly close to JUICE.
At UTAS, the Distributed FX (DiFX) software correlator [17] and the Difxcalc [18] interferometer model calculator was used to correlate VLBI data post-observation. Previous PRIDE phase referencing experiments used the SFXC software correlator [19] and in-house tools developed at the Joint Institute for Very Long Baseline Interferometry European Research Infrastructure Consortium (JIVE) specifically for PRIDE. This is the first attempt at correlating PRIDE experiments with the DiFX software correlator [17], the other major software correlator for VLBI used globally.
Correlation for the spacecraft was performed using the near-field version of DiFX (version 2.6.2), with the JUICE SPICE kernel6 and NASA’s Planetary Data System Navigation Node7 used. The Duev model was used, which solves the light-time equation twice to determine the near-field delay [14]. This was developed as part of the PRIDE package and demonstrated successfully with SFXC [3]. The Duev model became integrated into difxcalc in 2016, though further verification and comparison has not been conducted. This project began to address this gap. Following correlation in DiFX, the data was compiled into a FITS-IDI file for further analysis in AIPS or CASA. It was beyond the scope of this study to implement this stage of the data processing pipeline, however the future implementation at UTAS will use CASA [20].