491

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The Tektronix 491 is a spectrum analyzer with a frequency range of 10 MHz to 12.4 GHz (up to 40 GHz with external waveguide mixers). The 491 was introduced in August 1966. Due to severe performance limitations, the 491 was replaced by the completely redesigned 492 in 1980.

Specifications

Frequency Range
  • Coaxial Input Bands 10 MHz to 12.4 GHz (Band A-1 10 MHz to 275 MHz; Bands B-2 & 3: 275 MHz to 2 GHz; Bands C-4, 5, & 6: 1.5 GHz to 12.4 GHz)
  • External Waveguide mixers: 12.4 MHz to 40 GHz (Band 7 (Ku) 12.4 GHz to 18 GHz; Band 8 (K) 18 GHz to 26.5 GHz, (Ka) 18 GHz to 40 GHz)
Dispersion Range (plus 0 Hz) 200 kHz/div to 10 MHz/div in 1−2−5 sequence
Resolution Bandwidth 1 kHz to 100 kHz (6 dB)
Input impedance 50 Ω
Input Power max. −30 dBm for linear operation, +15 dBm (25 mW) diode mixer power limit
IF Attenuator Range 0 dB to 51 dB, in combinations of 1, 2, 4, 8, 16, and 20 dB
Sweep Speed Range 0.5 s/div to 10 µs/div in 1, 2, 5 sequence; Uncalibrated to approx 1.25 s/div
Triggering Modes Internals, External, and Line; 100 V maximum input (DC + peak AC)
Dynamic Range 80 dB (Max sensitivity of −110 dBm minus Max input power of −30 dBm); display range ≥40 dB
Calibrator Frequency 200 MHz
Weight 13.6 kg / 30 lbs (Rackmount version 18 kg / 40 lbs)
Power 90−136 and 180−272 VAC in six ranges, 48−440 Hz. At 115 VAC, 60 Hz, 55 W
Front panel inputs/outputs
  • RF INPUT (A) BNC connector (50 Ω, 10 MHz to 275 MHz)
  • RF INPUT (B) N connector (50 Ω, 275 MHz to 2 GHz)
  • WAVEGUIDE (C) N connector (50 Ω, 12.4 GHz to 40 GHz)
  • MARKERS OUT/EXT REF FREQ IN BNC connector: 1 MHz marker output when INT REF FREQ set to ON, otherwise PLL reference frequency input (1−5 MHz, 1−5 Vp-p)
Rear panel inputs/outputs

Options

  • Opt. 01: Limit Frequency Range to 10 MHz to 2 GHz
  • Opt. 02: Limit Frequency Range to 1.5 GHz to 40 GHz

Pictures