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Tektronix 494A
21 GHz Spectrum Analyzer
Tektronix 494A

Produced from 1988 to 1993

Manuals – Specifications – Links – Pictures

The Tektronix 494A/494AP 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.

Key Specifications

Frequency 10 kHz to 21 GHz (coaxial), up to 325 GHz using external waveguide mixers
Frequency Span 10 Hz to 10 GHz in 1–2–5 sequence (plus 0 Hz and MAX)
Resolution Bandwidth 10 Hz to 3 MHz in decade steps (-6 dB bandwidth)
RF Input 50 Ω; max. +30 dBm (1 W) CW or 75 W peak pulse (1 µs, 0.1% duty factor)
RF Attenuator 0 dB to 60 dB, 10 dB steps
Reference Level –117 dBm to +30 dBm
Sweep Speed 10 sec/div to 20 µs/div in 1–2–5 sequence
Video Bandwidth 0.3 Hz to 30 kHz
Triggering Modes Free Run, Line, Video, Single, External
Displayed Average Noise −30 dBm to −131 dBm
Display Dynamic Range 90 dB
Calibrator (Cal out) 50Ω, -20 dBm ±0.3 dB at 100 MHz
Weight 22.2 kg (48 lbs)
Power 90 − 132 VAC, 48 to 440 Hz; 180 – 250 VAC, 48 to 440 Hz, 210 W max
Operating Environment –15 °C to +55 °C; Humidity: Five cycles (120 hours) MIL-STD-810; Altitude: Up to 4.6 km (15,000 ft)


  • Opt. 07: 75 Ω dBmV input and calibration in addition to the normal 50Ω dBm input and calibration. (Not combinable with Opt. 21 and 22; no external mixer capability). Include 42-inch 75–Ω BNC-BNC coax cable and BNC male to “F” female adapter.
  • 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. 23: GRASP software, PC2A interface, and GPIB cable
  • Opt. 27: Epson LT-386SX, GRASP software, PC2A interface, and GPIB cable
  • Opt. 28: Compaq Deskpro 386S, Model 40, GRASP software, PC2A interface, and GPIB cable
  • Opt. 39: Non-lithium (Silver) batteries for battery-backed memory
  • Opt. 41: (all except 495P) Digital Microwave Radio Measurement Enhancement package
  • Opt. 42: Replaces MARKER/VIDEO input port on the rear panel with a 110 MHz IF output port that provides a 3 dB signal bandwidth ≥4.5 MHz
  • Opt. 45: MATE/CIIL language interface



Front panel inputs/outputs are: RF INPUT 50Ω N connector (Input connector for RF signals to 21 GHz. If input signal has a dc component use a blocking capacitor in line with the signals); CAL OUT BNC connector (Calibrator output provides -20 dBm 100 MHz signal and a comb of frequency markers 100 MHz apart); 1ST LO OUTPUT SMA connector (Provides access to the output of the 1st local oscillator. Must be terminated into 50 Ω when they are not connector to an external device); 2ND LO OUTPUT SMA connector (Provides access to the output of the 2nd local oscillator. Must be terminated into 50 Ω when they are not connector to an external device); EXTERNAL MIXER RF INPUT TNC connector (50 Ω); and Camera Power.

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 50 Ω 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 (B053575 AND UP) female DB25 connector (Provides bidirectional access to the instrument bus. For instruments B053574 and below, this connector has no application.); IEEE STD 488 PORT GPIB interface (Added to all "P" suffixed instruments)

Accessories originally included

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; rear connector shield; Power Cord; spare fuses; CRT filter set consisting of amber and gray light filters plus mesh filter