SRP4 Communication System Test Part

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SRP-4 Communication System Test - Part 1

• V. Edward Burket III

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Purpose

• Part one of the communication system test
  experimentally determines
• the carrier power level necessary at the receive
  antenna flange to obtain a clean demodulated
  signal from the Microdyne receivers video
  output.
• signal strength output voltages that correspond
  to carrier power levels at the antenna flange

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Test Setup
IF BW 3300 KHZ VIDEO BW 500 KHZ
F 2.218 GHZ
MOD BW 3 MHZ
L 4.4 dB
HP8780A Signal Generator
Microdyne Receiver
50 ft. Low Loss Coax
P_out
FM mod.
Video Out
50 kHz 1Vp-p
Function Generator
O-Scope
Signal Strength Output Voltage
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Comments on Test Setup

• The HP8780A signal generator simulates the input
  at the receive antenna flange.
• For the actual SRP-4 mission, a low noise
  amplifier with a gain of 20 dB will be inserted
  between the receive antenna flange and the coax
  cable.

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P_out vs. Signal Strength Output
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P_out vs. Carrier Threshold
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P_out vs. Video Signal Quality
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Accounting for Noise

• In a communication system, noise power is
  received in addition to the carrier power.
• Since the signal generator is matched to the 50
  ohm coax at the antenna flange point simulated in
  the test, the total noise power at the flange is
  
• NikTB(1.3810-23 J/K)(290 K)(3300 KHz)
  -138.8 dBW -108.8 dBm.

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Minimum Carrier to Noise Ratio

• Since the input noise power at the simulated
  antenna flange is -108.8 dBm, and the minimum
  carrier input power that yields a clean
  demodulated video signal output is -85 dBm,
  the minimum input carrier to noise ratio is
• -85 dBm - (-108.8 dBm) 23.8 dB.

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Comparing Test Noise Power with Expected Noise
Power

• Under actual conditions, a maximum antenna noise
  temperature of 300 K is expected for a total
  input noise power of
• Ni (1.3810-23 J/K)(300 K)(3300 kHz)
  -138.6 dBW -108.6 dBm
• This is virtually the same as the test input
  noise power of -108.8 dBm.

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SRP-4 Link Budget EIRP

• Transmitter Output Power, Pt 34 dBm
• Worst Case Transmitter Antenna Gain Gt
  - 10 dB
• EIRP Pt Gt 24 dBm

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SRP-4 Link Budget Receive Antenna Gain and
Beamwidth

• Theoretical gain of 1.22 meter antenna with 0.55
  efficiency and free-space wavelength of 13.5 cm
  Gr 38.5 dB
• Half-Power Beam Width (approximate)
• HPBW 7.75 degrees
• Pointing loss assumed for link budget
• L_p 3 dB

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SRP-4 Link Budget Space Loss

• At apogee, assume x 30 km and y 92 km. Then
  slant range 96.8 km and space loss at apogee
• L_sa 138.7 dB
• On launch rail, assume x 1.6 km. Then space
  loss on rail
• L_sr 103. 5 dB

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SRP-4 Link Budget at Apogee
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SRP-4 Link Budget at Launch Rail
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Conclusions

• The SRP-4 communication link has a margin of 4.8
  dB at apogee. This margin will be improved with
  the addition of the LNA.
• Pointing the receive antenna directly at the
  rocket while it is on the launch rail will not
  overload the receiver front end.