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Tektronix 494
21 GHz Spectrum Analyzer
Tektronix 494

Produced from 1985 to 1989

Manuals – Specifications – Links – Pictures

The Tektronix 494 is a spectrum analyzer with a frequency range of 10 kHz to 21 GHz in coax, and up to 325 GHz with external waveguide mixers. The P suffix designation indicates GPIB Programmability. The minimum resolution bandwidth is 30 Hz, and provides measurement resolution proportional to the frequency accuracy or span.

In 1988, the 494A /494AP successor model was introduced.

Front panel inputs/outputs are: RF INPUT 50Ω (N connector), CAL OUT (BNC connector), LO OUTPUTS (SMA connectors), EXTERNAL MIXER RF INPUT (TNC connector), and Camera Power. The LO outputs can be used to connect an external waveguide mixer like the WM490 series, or to connect a TR503 tracking generator.

Rear panel inputs/outputs are: PROBE POWER (Provides operating voltages (+5V, -15 V, +15 V; 100 mA max each) for active probes); HORIZ|TRIG (EXT IN) BNC connector (A dual function connector: When in External Triggering mode the connector is an AC coupled input for trigger signals. When the TIME/DIV selection is EXT the connector is a DC coupled input for horizontal sweep voltages); MARKER/VIDEO (EXT IN) BNC connector (Available on instruments without Opt. 42 only. See 110 MHz IF for Opt. 42 instruments. This connector interfaces the spectrum analyzers with a Tektronix 1405 TV Adapter to display an externally-generated marker) 110 MHz IF (OUTPUT) BNC connector (Available on Opt. 42 utilizing the HORIZ (OUTPUT) connector. This connector provides 110 MHz IF output with a bandwidth greater than 5 MHz. Input external video signals into the PEN LIFT connector); HORIZ (OUTPUT) BNC connector (Supplies a 0.5 V/div horizontal signal); VERT (OUTPUT) BNC connector (Provides access to the video signal with 0.5 V for each division of displayed video above or below the center line.)

NOTE: Both HORIZ and VERT output signals are driven from digital storage if it is on. Both signals are driven from the analyzer sweep and video amplifier stage if digital storage is off;

PEN LIFT (OUTPUT) BNC connector (Provides access to a TTL compatible signal to lift the pen of a chart recorder during sweep retrace. This signal is always derived from the spectrum analyzer sweep. In Opt. 42 instruments, use this connector to input external video signals if pin 1 of the ACCESSORIES connector is grounded; 10 MHz IF (OUTPUT) BNC connector (Provides access to the output of the 10 MHz IF); EXT REF IN BNC connector (A 50Ω input for a 1, 2, 5, or 10 MHz external reference signals, within -15 dBm to +15 dBm level. Input signals must be a sinewave with a duty cycle symmetry of 40% to 60%, or ECL or TTL); J104 ACCESSORY female DB25 connector (Provides external video input selector on Pin 1 and external preselector out on Pins 2 and 3, Pin 5 is ground.); IEEE STD 488 PORT GPIB interface (Added to all "P" suffixed instruments)


Frequency Range
  • 10 kHz to 1.8 GHz
  • 1.7 GHz to 5.5 GHz
  • 3 GHz to 7.1 GHz
  • 5.4 GHz to 18 GHz
  • 15 GHz to 21 GHz
  • External Waveguide mixers: 18 GHz to 325 GHz
Frequency Span Range (plus 0 Hz and MAX) 50 Hz/Div to 500 MHz/Div in 1, 2, 5 sequence
Resolution Bandwidth Range (-6 dB bandwidth) 30 Hz, then 100 Hz to 1 MHz in decade steps
RF Input impedance 50Ω
Maximum Safe Input Power CW: +30 dBm (1 W); Pulse: 75 W Pk (1 µS pulse, 0.1% duty factor)
RF Attenuator Range 0 dB to 60 dB, 10 dB steps
Reference Level Range -117 dBm to +40 dBm
Sweep Speed Range 10 sec/div to 20 µs/div in 1, 2, 5 sequence
Video Bandwidth Filter
  • Normal
  • Wide 1/30 of resolution bandwidth
  • Narrow 1/300 of resolution bandwidth
Triggering Modes Free Run, Line, Video, Single, External
Display Dynamic Range 80 dB
Calibrator (Cal out) 50Ω, -20 dBm ±0.3 dB at 100 MHz
Included Accessories Operator’s Manual; Programmer Manual; 6-ft 50Ω coaxial cable N-N; 18-inch 50Ω coaxial cable BNC-BNC; N male to BNC female adapter; Diplexer Assembly; Power Cord; spare fuses; CRT filter set consisting of amber and gray light filters plus mesh filter
Weight 24 kg (52 lbs) with standard accessories
Power 90 − 132 VAC, 48 to 440 Hz; 180 – 250 VAC, 48 to 440 Hz. At 115 VAC, 60 Hz, 210 W max
Operating Atmospherics Temperatures: -15 °C to +55 °C; Humidity: Five cycles (120 hours) MIL-STD-810; Altitude: Up to 4.6 km (15,000 ft)
GPIB Characteristics In accordance with IEEE Standard 488-1978 implemented as SH1, AH1, T5, L3, SR1, RL1, PP1, DC1, DT1, and C0


  • Opt. 08: Delete external Mixer capability
  • Opt. 12: Help mode text in English + German
  • Opt. 13: Help mode text in English + French
  • Opt. 14: Help mode text in English + Spanish
  • Opt. 20: General Purpose 12.4-40 GHz Waveguide Mixer Set
  • Opt. 21: High performance 18 to 40 GHz WM490 Series Waveguide Mixer Set
  • Opt. 22: Same as Opt. 21 plus WM490U (40-60 GHz) Waveguide Mixer
  • Opt. 30: Rackmount with front panel I/O
  • Opt. 31: Rackmount with rear panel I/O
  • Opt. 32: Benchmount
  • Opt. 41: Digital Microwave Radio Measurement Enhancement package: Provides wider bandwidth preselector, 30Hz video filter with 100 kHz resolution bandwidth and a 5 MHz/Div span.
  • Opt. 42: Replaces MARKER/VIDEO input port on the rear panel with a 110 MHz IF output port that provides a 6 dB signal bandwidth ≥ 5 MHz
  • Opt. 45: MATE/CIIL language interface