RF front end P' Gorham UH

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A N I T A
RF front endP. GorhamUH
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Radio frequency subsystem

• Three major subsystems
• Antennas
• RFCMs
• SHORTSURF receiving section in the IEB
• No notch filters (we will be subject to 429MHz
  interference around launch)
• Compression
• begins at -32 dBm input to Miteq,
• ZKL1R5 1dBcmp at -67dBm
• (more below)
• 1W Miteq limiter spec not verified
• KL found failure at 1W CW in June 2005, OK at 0.4
  W

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RFCM data

• Average gain, 75 dB
• Channel to channel variation, 2dB
• System temperature, average 150K over most of
  band, rises sharply at high end due to filter
  cable losses
• RMS noise voltages at room temperature, looking
  into 293K load
• CH1-4 90.6, 95.2, 94.0, 99.0 mV
• 94.7 mV rms average
• Expect 75mV in Antarctica

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Component sequence, noise figure

• Antenna --gt low loss cable (LMR400 or Heliax),
  1m
• expect lt30K from cable connectors
• Bandpass filters
• -0.3 to -0.8 dB gt 50K
• Coupler thru SMA semirigid into LNA. LNA gt
• 80-100K, incl. Connectors
• Design requirement is 200K, goal 150K.
  Requirement has been met on average over the band

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Dynamic range

• Current rms outputs (75mV rms) -9.5 dBm
• Pulse saturation occurs at about 1.8V (13 dBm)
  for 30 mV rms (-17.4 dBm) gt 35 dB dynamic
  range
• If we assume the same ceiling in V, we will have
  about 28 dB dynamic range -- but this needs to be
  confirmed

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highpass

• In band, 0.3dB over most of band, 3db at 180MHz,
  lt-50dB 110MHz
• We will get -30-40 dB at 150 MHz, not enough to
  block local VHF tranmitters from saturating us

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lowpass

• Final spec, -50dB _at_ 1610 MHz (Iridium), -70dB _at_
  2200MHz (TDRSS)
• These are adequate to avoid saturation of amps
  but we may lose some dynamic range if Iridium and
  TDRSS leak through to LNA

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Filter analysis for iridium 1610MHz

• Iridium transmitter is not optional
• Current LP filter scheme has two sets before
  trigger
• Iridium will not affect high-band triggering
• However, LNA (actually 2nd stage amp) is only
  shielded by 1 filter
• Iridium could push total RFCM power close to
  compression point
• Current filter typical performances indicate no
  more than 10, but we need to test!