Spectrum Environment of The Allen Telescope Array Site Selection Measurement Technology Results and

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Spectrum Environment ofThe Allen Telescope
ArraySite SelectionMeasurement
TechnologyResults and Plans

• Mike Davis, Jane Jordan and
• Tom Kilsdonk
• URSI Radio Science Meeting Boulder, 7 January
  2005

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The first three elements of the ATA at Hat Creek
Radio Observatory.
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Hat Creek HofstadterRanch Panoche New
Idria Leigh Ranch
Sites Considered
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Rendering of the completed ATA-350 at the Hat
Creek Radio Observatory.
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The Allen Telescope Array feed has a bandwidth
spanning 500 MHz to 11.2 GHz. The receiver
electronics are housed within the interior
spike, where they are cooled to 80 K.
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The pointy end of the feed, showing the
descrambling needed to feed the tapered-line
balun .
The tapered-line balun on a crystal-quartz
substrate mated to the wide bandwidth LNA.
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Block diagram of the ATA signal path, feeding
both an imaging correlator and phased array
back-ends
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High Resolution Spectrum Analyzer used for RFI
Study

• FIR Filters isolate twelve adjacent 2.5 MHz bands
• Polyphase Filters isolate 3584 subbands of 0.7
  kHz in each band
• FFT gt 1024 bins in each subband, 0.678 Hz apart
• Dual polarization gt 108 data points dumped
  every 0.75 s, or 1010 points per observation
• Processed in near real time to detect narrowband
  CW and pulsed signals, stationary or drifting

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Observing Procedure

• Point the telescope in a chosen direction
• Step through 1 to 10 GHz, 30 MHz at a time
• Record all detected signals above background
• Repeat the observations several times
• Move to a new pointing direction and start again

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Log(Number of detections) 1 to 10 GHz
Digital Audio Broadcast Satellites
TV Downlinks
Log N
Communications Satellites
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Comparison to Arecibo
L Band
S Band 1.0 to 1.8 GHz
1.6 to 3.2 GHz
AO
Hat Creek
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Plans Transient RFI Check

• RFI Surveys provide only a snapshot
• Transient interference is difficult to verify
• Even more difficult to locate its source(s)
• We are starting a transient RFI trial survey with
  OASIS software, using our existing Spectrum
  Analyzer

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Frequency Drifting Transmitter
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Summary

• Hat Creek has retained its quiet local spectrum
  environment
• Satellites are the most serious threat, as
  expected
• The RFI excision and nulling capabilities
  included in the array design are well justified.