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trimming/streamlinig; inroduction date per 1971 Tek calendar
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(trimming/streamlinig; inroduction date per 1971 Tek calendar)
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discontinued=1980 |
discontinued=1980 |
manuals=
manuals=
Need Service Manual
* [[Media:070-0598-01.pdf | Tektronix 491 Instruction Manual needed]]
* [[Media:070-0598-01.pdf| Tektronix 491 Instruction Manual {Qservice Scan} (PDF, OCR)]]
* [[Media:Tektronix_491_Maintenance_Manual_ARMY.pdf | Tektronix 491 Instruction Manual (US Army TM 9-6625-2467-15) (PDF)]]
* [[Media: Tektronix_491_Maintenance_Manual_ARMY.pdf | Tektronix 491 Instruction Manual {US Army Technical Manual TM 9-6625-2467-15} (PDF)]]
* [[Media:Tek_491_Catalog_Spec_1967.pdf | Tektronix 491 Introduction Spec (PDF, OCR)]]
* [[Media:050-0692-03.pdf| Tektronix 491 Band C Oscillator Replacement Modification (PDF, OCR)]]
* [[Media:Tek_491_Catalog_Spec_1979.pdf | Tektronix 491 Final Spec (PDF, OCR)]]
* [[Media:Tek 491 mod wa.pdf|Tektronix 491 Mod WA (PDF, needs OCR)]]
* ''Service manual needed ''
* [[Media:Tek 491 fcp nov 1966.pdf |Tektronix 491 Factory Calibration Procedure, November 1966 (PDF, needs OCR)]]
<small>
* [[Media:Tek_491_Catalog_Spec_1967.pdf| Tektronix 491 Introduction Spec (PDF, OCR)]]
'''Modifications and Calibration'''
* [[Media:Tek_491_Catalog_Spec_1979.pdf| Tektronix 491 Final Spec (PDF, OCR)]]
* [[Media:050-0692-03.pdf | Tektronix 491 Band C Oscillator Replacement Modification (PDF, OCR)]]
* [[Media:Tek 491 mod wa.pdf | Tektronix 491 Mod WA (PDF, needs OCR)]]
* [[Media:Tek 491 fcp nov 1966.pdf | Tektronix 491 Factory Calibration Procedure, November 1966 (PDF, needs OCR)]]
</small>
}}
}}
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 1966|introduced in August 1966]].  Due to severe performance limitations, the 491 was replaced by the completely redesigned [[492]] in 1980.


NOTE: Due to severe performance limitations, it was replaced by the completely redesigned 492 in 1980
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The '''Tektronix 491''' is a spectrum analyzer with a frequency range of 10 MHz to 40 GHz.  The minimum resolution bandwidth is 1 kHz, and provides measurement resolution proportional to the frequency accuracy or span. 
Front panel inputs/outputs are: RF INPUT (A) [[BNC connector]] (50Ω, 10 MHz to 275 MHz); RF INPUT (B) [[N connector]] (50Ω, 275 MHz to 2 GHz); WAVEGUIDE (C) [[N connector]] (50Ω, 12.4 GHz to 40 GHz); and a dual function 1 MHz MARKERS OUT [[BNC connector]] (With the INT REF FREQ in the ON position a 1 MHz marker outputs to this connector.  With the INT REF FREQ in the OFF position EXT REF FREQ IN “same” [[BNC connector]] accepts an external signal between 1 MHz and 5 MHz (1 to 5 V peak to peak) applied to the connector becomes the reference frequency for the phase lock operation).
Rear panel inputs/outputs are: TRIG IN [[BNC connector]] (20 Hz to 100 kHz, ≥0.2V); SAW OUT [[BNC connector]] (75mV/div); and RECORDER [[BNC connector]] (≥4 mV/div of displayed signal in LIN mode, DC-coupled, into 600Ω load impedance).
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<div style='text-align: center;'>Specifications based on final published documentation, unless otherwise specified.</div>
{{BeginSpecs}}
{{BeginSpecs}}
{{Spec | Frequency Range |
{{Spec | 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; and Bands C-4, 5, & 6: 1.5 GHz to 12.4 GHz)
* Coaxial Input Bands 10 MHz to 12.4 GHz  (Band A-1 10 MHz to 275 MHz; Bands B-2 &amp; 3: 275 MHz to 2 GHz; Bands C-4, 5, &amp; 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; and Bands 8: (K) 18 GHz to 26.5 GHz, and (Ka) 18 GHz to 40 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)}}
CAUTION: Signals stronger than +15 dBm applied to the input or mixer will damage or burn out the mixer diodes }}
{{Spec | Dispersion Range | (plus 0 Hz) 200 kHz/div to 10 MHz/div in 1−2−5 sequence }}
{{Spec | Dispersion Range (plus 0 Hz) | 200 kHz/div to 10 MHz/div in 1-2-5 sequence }}
{{Spec | Resolution Bandwidth | 1 kHz to 100 kHz (6 dB) }}
{{Spec | Resolution Bandwidth Range | 6 dB bandwidths from 1 kHz to 100 kHz }}
{{Spec | Input impedance | 50 Ω }}
{{Spec | RF Input impedance | 50 Ω }}
{{Spec | Input Power | max. −30 dBm for linear operation, +15 dBm (25 mW) diode mixer power limit }}
{{Spec | Maximum Safe Input Power | -30 dBm for linear operation and +15 dBm (25 mW) diode mixer power limit }}
{{Spec | IF Attenuator Range | 0 dB to 51 dB, in combinations of 1, 2, 4, 8, 16, and 20 dB }}
{{Spec | IF Attenuator Range | 0 dB to 51 dB, in combinations of 1, 2, 4, 8, 16, and 20 dB }}
{{Spec | Sweep Speed Range | 0.5 s/div to 10 µs/div in 1, 2, 5 sequence; Uncalibrated to approx 1.25 s/div }}
{{Spec | Sweep Speed Range | 0.5 s/div to 10 µs/div in 1, 2, 5 sequence; Uncalibrated to approx 1.25 s/div }}
{{Spec | Triggering Modes | Internals, External, and Line. 100 V maximum input (DC + peak AC) }}
{{Spec | Triggering Modes | Internals, External, and Line; 100 V maximum input (DC + peak AC) }}
{{Spec | Display Dynamic Range | ≥40 dB }}
{{Spec | Display Dynamic Range | ≥40 dB }}
{{Spec | Dynamic Range | 80 dB (Max sensitivity of -110 dBm minus Max input power of -30 dBm) }}
{{Spec | Dynamic Range | 80 dB (Max sensitivity of −110 dBm minus Max input power of −30 dBm) }}
{{Spec | Calibrator Frequency | 200 MHz }}
{{Spec | Calibrator Frequency | 200 MHz }}
{{Spec | Included Accessories |Two Instruction Manuals; 6-ft, 50Ω coaxial cable, BNC-BNC; 6-ft, 50Ω coaxial cable, N-N; 2-ft, 50Ω coaxial cable, TNC-TNC; 12.4 GHz to 18 GHz waveguide mixer; 18 GHz to 26.5 GHz waveguide mixer; 26.5 to 40 GHz waveguide mixer; 10 dB attenuator N type fittings; 20 db attenuator N type fittings; two BNC male to N female adapters; two BNC female to N male adapters; Waveguide mixer adapter; power cord; dust and rain cover; 3 to 2 wire adapter; blue light filter; amber light filter; clear CRT protector plate; ornamental ring; mesh filter (installed); two one-ampere fuses; and 1/2 –ampere fuse }}
{{Spec | Weight | 13.6 kg / 30 lbs (Rackmount version 18 kg / 40 lbs) }}
{{Spec | Weight | Portable: 13.6 kg (30 lbs) ; Rackmount: 18 kg (40 lbs) }}
{{Spec | Power | 90−136 and 180−272 V<sub>AC</sub> in six ranges, 48−440 Hz.  At 115 V<sub>AC</sub>, 60 Hz, 55 W }}
{{Spec | Power | 90 − 136 V<sub>AC</sub> in three ranges, 48 to 440 Hz; 180 – 272 V<sub>AC</sub> in three ranges, 48 to 440 Hz.  At 115 V<sub>AC</sub>, 60 Hz, 55 W }}
{{Spec | Front panel inputs/outputs |  
{{Spec | Operating Atmospherics | Temperatures: -15 °C to +55 °C; Humidity: Five cycles (120 hours) of MIL-STD-202C Method 106B; Altitude: Up to 4.6 km (15,000 ft) }}
*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 V<sub>p-p</sub>) }}
{{Spec | Rear panel inputs/outputs  |
*TRIG IN [[BNC connector]] (20 Hz to 100 kHz, ≥0.2 V)
*SAW OUT [[BNC connector]] (75 mV/div)
*RECORDER [[BNC connector]] (≥4 mV/div of displayed signal in LIN mode, DC-coupled, into 600 Ω) }}
{{EndSpecs}}
{{EndSpecs}}


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