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{{Oscilloscope Sidebar |
{{Instrument Sidebar
title=Tektronix 491 |
|manufacturer=Tektronix
summary=Spectrum Analyzer 10 MHz to 40 GHz |
|class=Spectrum Analyzer
image=Tek 491.jpg |
|model=491  
caption=Tektronix 491 |
|summary=40 GHz Spectrum Analyzer
introduced=1967 |
|image=Tek 491.jpg  
discontinued=1980 |
|caption=Tektronix 491  
manuals=
|introduced=1966
Need Service Manual
|discontinued=1980  
* [[Media:070-0598-01.pdf| Tektronix 491 Instruction Manual {Qservice Scan} (PDF, OCR)]]
|designers=Gene Kauffman;
* [[Media: Tektronix_491_Maintenance_Manual_ARMY.pdf | Tektronix 491 Instruction Manual {US Army Technical Manual TM 9-6625-2467-15} (PDF)]]
|manuals=
* [[Media:050-0692-03.pdf| Tektronix 491 Band C Oscillator Replacement Modification (PDF, OCR)]]
* [[Media:070-0598-01.pdf|Tektronix 491 Instruction Manual 070-0598-01]]''
* [[Media:Tek 491 mod wa.pdf|Tektronix 491 Mod WA (PDF, needs OCR)]]
* [[Media:Tektronix_491_Maintenance_Manual_ARMY.pdf | Tektronix 491 Instruction Manual (US Army TM 9-6625-2467-15)]]
* [[Media:Tek 491 fcp nov 1966.pdf |Tektronix 491 Factory Calibration Procedure, November 1966 (PDF, needs OCR)]]
* [[Media:Tek_491_Catalog_Spec_1967.pdf | Tektronix 491 Introduction Spec]] (OCR)
* [[Media:Tek_491_Catalog_Spec_1967.pdf| Tektronix 491 Introduction Spec (PDF, OCR)]]
* [[Media:Tek_491_Catalog_Spec_1979.pdf | Tektronix 491 Final Spec]] (OCR)
* [[Media:Tek_491_Catalog_Spec_1979.pdf| Tektronix 491 Final Spec (PDF, OCR)]]
 
<small>
'''Modifications and Calibration'''
* [[Media:050-0692-03.pdf | Tektronix 491 Band C Oscillator Replacement Modification]] (OCR)
* [[Media:Tek 491 mod wa.pdf | Tektronix 491 Mod WA]]
* [[Media:Tek 491 fcp nov 1966.pdf | Tektronix 491 Factory Calibration Procedure, November 1966]]
</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
---------------------------------------------------------
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 MGHz 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).
---------------------------------------------------------
<div style='text-align: center;'>Specifications based on final published documentation, unless otherwise specified.</div>
{{BeginSpecs}}
{{BeginSpecs}}
{{Spec | Frequency Range |
{{Spec | Frequency |
* 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 | (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 | 50 Ω, max. −30 dBm for linear operation, +15 dBm (25 mW) diode mixer power limit }}
{{Spec | RF Input impedance | 50 Ω }}
{{Spec | IF Attenuator  | 0 dB to 51 dB, in combinations of 1, 2, 4, 8, 16, and 20 dB }}
{{Spec | Maximum Safe Input Power | -30 dBm for linear operation and +15 dBm (25 mW) diode mixer power limit }}
{{Spec | Sweep Speed | 0.5 s/div to 10 µs/div in 1, 2, 5 sequence; Uncalibrated to approx 1.25 s/div }}
{{Spec | IF Attenuator Range | 0 dB to 51 dB, in combinations of 1, 2, 4, 8, 16, and 20 dB }}
{{Spec | Triggering Modes | Internals, External, and Line; 100 V maximum input (DC + peak AC) }}
{{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 | Dynamic Range | 80 dB (Max sensitivity of −110 dBm minus Max input power of −30 dBm); display range ≥40 dB }}
{{Spec | Triggering Modes | Internals, External, and Line. 100 V maximum input (DC + peak AC) }}
{{Spec | Calibrator | 200 MHz }}
{{Spec | Display Dynamic Range | ≥40 dB }}
{{Spec | Weight | 13.6 kg / 30 lbs (Rackmount version 18 kg / 40 lbs) }}
{{Spec | Dynamic Range | 80 dB (Max sensitivity of -110 dBm minus Max input power of -30 dBm) }}
{{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 | Calibrator Frequency | 200 MHz }}
{{Spec | Front panel  |  
{{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 }}
* RF INPUT (A) [[BNC connector]] (50 Ω, 10 MHz to 275 MHz)
{{Spec | Weight | Portable: 13.6 kg (30 lbs) ; Rackmount: 18 kg (40 lbs) }}
* RF INPUT (B) [[N connector]] (50 Ω, 275 MHz to 2 GHz)
{{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 }}
* WAVEGUIDE (C) − receptacle that accommodates either a coaxial mixer, 119-0096-00, with an N connector input for 1.5 to 12.4 GHz, or a [[119-0104-00]] waveguide mixer adapter connecting to external mixers for up to 40 GHz.
{{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) }}
* 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  |
* 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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* Opt. 01: Limit Frequency Range to 10 MHz to 2 GHz
* Opt. 01: Limit Frequency Range to 10 MHz to 2 GHz
* Opt. 02: Limit Frequency Range to 1.5 GHz to 40 GHz
* Opt. 02: Limit Frequency Range to 1.5 GHz to 40 GHz
==Prices==
1979: $10,700 ($41,800 in 2022 Dollars)
According to an [[Media:Tek Schottky Diodes Memo rot.pdf|internal memo]], in 1979 annual sales were estimated at 172 units.


==Pictures==
==Pictures==
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</gallery>
</gallery>


[[Category: Spectrum Analyzers]]
==Components==
{{Parts|491}}
 
 
[[Category:Spectrum analyzers]]

Latest revision as of 06:10, 27 April 2024

Tektronix 491
40 GHz Spectrum Analyzer
Tektronix 491

Produced from 1966 to 1980

Manuals
Manuals – Specifications – Links – Pictures

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.

Key Specifications

Frequency
  • 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 (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 50 Ω, max. −30 dBm for linear operation, +15 dBm (25 mW) diode mixer power limit
IF Attenuator  0 dB to 51 dB, in combinations of 1, 2, 4, 8, 16, and 20 dB
Sweep Speed 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 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
  • 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) − receptacle that accommodates either a coaxial mixer, 119-0096-00, with an N connector input for 1.5 to 12.4 GHz, or a 119-0104-00 waveguide mixer adapter connecting to external mixers for up 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

Options

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

Prices

1979: $10,700 ($41,800 in 2022 Dollars)

According to an internal memo, in 1979 annual sales were estimated at 172 units.

Pictures

Components

Some Parts Used in the 491

Part Part Number(s) Class Description Used in
155-0157-00 155-0157-00 Monolithic integrated circuit digital storage vertical control 7L5 • 7L14 • 7L18 • 491 • 492 • 492A • 492BP • 492PGM • 494 • 494A • 495 • 496 • 497P
155-0158-00 155-0158-00 Monolithic integrated circuit digital storage horizontal control 7L5 • 7L14 • 7L18 • 491 • 492 • 492A • 492BP • 492PGM • 494 • 494A • 495 • 496 • 497P
1N3714 152-0081-00 Discrete component 2.2 mA, 25 pF germanium tunnel diode 546 • 547 • 556 • 21A • 22A • 3B1 • 3B2 • 3B3 • 422 • 491 • 283
1N3717 152-0381-00 • 152-0125-00 Discrete component 4.7 mA, 25 pF tunnel diode 1L40 • 1S1 • 1S2 • 11B1 • 11B2 • 11B2A • 147A • 1470 • 148 • 21A • 22A • 3B4 • 3B5 • 408 • 432 • 434 • 453 • 453A • 454 • 466 • 491 • 5T3 • 544 • RM544 • 546 • RM546 • 547 • RM547 • 556 • RM556 • 7B70 • 7B71 • 7D11
STD704 152-0125-00 Discrete component 4.7 mA tunnel diode 1L40 • 1S1 • 11B1 • 11B2 • 11B2A • 147 • R147 • 147A • R147A • 1470 • 148 • R148 • 148-M • 149 • R149 • 149A • R149A • 21A • 22A • 3B4 • 3B5 • 408 • 432 • 434 • 453 • 453A • 454 • 464 • 465 • 466 • 491 • 5T3 • 544 • RM544 • 546 • RM546 • 547 • RM547 • 556 • RM556 • 7B70 • 7B71 • 7D11
T4910 CRT CRT 491
TD714 152-0402-00 Discrete component 2.2 mA, 25 pF tunnel diode 1401 • 1401A • 283 • R283 • 3B2 • 3B3 • 422 • 491 • 546 • RM546 • 547 • RM547 • 556 • RM556 • SPG11 • SPG12
Y1641 154-0506-00 • 154-0510-00 Vacuum Tube (Triode) SHF cermet triode 1L20 • 491
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