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Trials were undertaken recently at Parkes with a small, potentially
portable, VHF antenna for pulsar detection to explore the potential for
global timing event synchronization. Experiments were conducted east
of the Parkes 64m dish using a single Murchison Widefield Array (V3)
antenna as the receptor, as used in 4x4 array tiles at the MRO. The
antenna is a broadband VHF 70-300MHz dual polarization bowtie dipole
structure with a span of 74cm. When positioned 10cm above a wire mesh
ground plane the antenna field pattern has a broad lobe maximized
skyward with a drop in gain below 30 degrees elevation, improving
rejection to terrestrial radio interference. The dipole elements
connect to a balanced HEMT FET Low Noise Amplifier design located in
the plastic hub of the antenna. The LNA noise contribution is less
than the galactic sky noise contribution with a mid-band gain of
19dB. Using a single polarization output, we attenuate (>20dB)
unwanted FM radio signals with a 88-108MHz band-stop filter then
directly modulate a DFB laser diode RFoF single-mode fiber span over
500m to the DFB4 1GS/s digitizer located in the tower. The antenna and
fiber optics in the paddock are powered by a small 12V7AHr battery. No
pulsar detections were made but a second attempt with an improved
signal chain dynamic range and different DFB4 settings is planned. The
weather during the experiment could only be described as atrocious,
with heavy snow at Orange on the return to Marsfield!
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