492

Manuals – Specifications – Links – Pictures

The Tektronix 492 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 (492PGM N/A). The P suffix designation indicates GPIB Programmability.

During the lifespan of the instrument, the specifications and included options were altered several times. A major upgrade was the introduction of the 492A in 1987 which added marker functionality and resolution bandwidths and the 492BP in 1989 which added a counter and increased the displayed dynamic range. The 492PGM is a cost reduced version introduced in 1990. Also see 49X Series Comparison.

Regarding the 492, Linley Gumm says,

Given how complicated it was, many people contributed to the design. I currently have a list of 20 people. The problem is that I’m sure that I am missing several people and I hate to submit a list without them.

The 492 was designed at the request of the military. They asked for a modern replacement of the 491. It was required that it provide coaxial input coverage of the lower microwave bands (~18 GHz), be very rugged, be a one person carry and fit through a submarine hatch. There was a lot more than that of course.

When the 492 program started I was the project leader of the 7L18 and was still working to finish it off. The 7L18 was the first instrument at Tektronix to use a microprocessor. We had worked long and hard to learn how to electronically switch and control all the elements that were controlled by physical switch closures in the earlier instruments.

Understand that to position the frequency of a YIG filter correctly with respect to the frequency of a YIG oscillator one must generate very quiet DC voltages accurate to roughly 1 part in 20,000 (i.e. 1 MHz in 18 GHz), so new control techniques were required. Plus the TEK-made YIG filter designed for the 7L18 was therefore ready for use in the 492.

We had also learned quite a number of things not to do and this was also used to anchor the 492 program. I say this to note that most of the long lasting, “classic”, Tektronix products were often the second, but more often the third generation product by the same design group. The 492 was definitely a second generation product in its use of microwave components and a microprocessor based control system; perhaps a third if you lump the 7L12, 7L13 (microwave systems) and the 7L5 (electronic bus control system) together as a first generation.

Larry Lockwood led the first part of the program. He defined the RF and microwave frequency conversion architecture of the 492. As the program progressed, Steve Morton became the project manager of the initial 492 program. Recognize that beyond that initial project, follow-on design work went on for years as new features were added. Further, after their initial design work in the initial portion of the project, designers often went on to do rather different subsystems in the follow-ons.

I worked on the 492 as a circuit designer in the initial design and in several other roles later, none of which were leadership roles.

The other people I can recall having worked on the 492 at some point in its life were: Robert Alm, Bob Bales, Carlos Beeck, Bill Benedict, Craig Bryant, Russell Brown, Wes Hayward, David Leatherwood, Gordon Long, Dave Morton, Bill Peterson, David Shores, Steve Skidmore, Dennis Smith, Phil Snow, Leighton Whitset, and Norman Witt.

Be aware my spelling is often “inventive”. There are at least two other names I can’t bring to mind.

Key Specifications

Frequency	Coaxial Input Bands: 10 kHz to 21 GHz External Waveguide mixers: 10 kHz to 325 GHz (applies to 492BP not 492PGM)
Frequency Span	492BP: 100 Hz/div to 10 GHz/div; 492PGM: 200 MHz to 1 GHz; both in 1, 2, 5 sequence; plus 0 Hz and MAX
Resolution Bandwidth (-6 dB bandwidth)	492BP: 100 Hz to 3 MHz; 492PGM: 1 kHz to 3 MHz; both in decade steps
RF Input	50 Ω, max. +30 dBm (1 W) CW; / 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, 1−2−5
Video Bandwidth	492BP: 0.3 Hz to 30 kHz; 492PGM: 3 Hz to 30 kHz
Memory	NVRAM for up to 9 waveform displays, up to 10 front panel setups, plus 8 K for programming macros
Triggering Modes	Free Run, Line, Video, Single, External
Displayed Average Noise	−30 dBm to −131 dBm
Display Dynamic Range	492BP: 90 dB; 492PGM: 80 dB
Calibrator (Cal out)	50 Ω, -20 dBm ±0.3 dB at 100 MHz
Weight	492BP: 21.8 kg (47 lbs) 492PGM: 21.3 kg (46 lbs)
Power	90 − 132 VAC, 48 to 440 Hz; 180 – 250 VAC, 48 to 440 Hz. At 115 VAC, 60 Hz, 210 W max

Options

• Opt. 01: Internal Preselection. (Limits the first band to 1.8 GHz instead 4.2 GHz). Later became standard
• Opt. 02: Digital Storage. Later became standard
• Opt. 03: Frequency Stabilization & 100 Hz Resolution. Later became standard
• Opt. 07: 75 Ω dBmV input and calibration in addition to the normal 50 Ω 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: (492BP) High performance 18 to 40 GHz WM490 Series Waveguide Mixer Set
• Opt. 22: (492BP) 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: 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: (all except 492PGM) MATE/CIIL language interface

Links

• Comparison of 492 with 494 and 7L18
• 49x Service notes @ John Miles KE5FX
• KE5FX GPIB toolkit
• ROM replacement
• Tek 492 DIY USB interface project
• Waveguide Mixers for 492 and 7L18
• YouTube: Tektronix 492 and 496 Portable Spectrum Analyzers
• 067-1137-99 GPIB to accessory controller

Documents Referencing 492

Document	Class	Title	Authors	Year	Links
Tekscope 1980 V12 N1.pdf	Article	Packaging A Spectrum Analyzer for Performance, Maintainability and Survival	Carlos Beeck	1980	492
Tekscope 1980 V12 N1.pdf	Article	A First Converter With Field Replaceable Diodes	Phil Snow	1980	492
Tekscope 1980 V12 N1.pdf	Article	A Switching Power Supply For The 492 Spectrum Analyzer	David Leatherwoood	1980	492
Tekscope 1980 V12 N1.pdf	Article	A Portable High-Performance Microwave Spectrum Analyzer	Dave Morton	1980	492
Tekscope 1980 V12 N1.pdf	Article	The Tektronix 492 Is A New-Generation Spectrum Analyzer	Morris Engelson	1980	492
Tekscope 1980 V12 N1.pdf	Article	Making Measurements with the 492	Morris Engelson	1980	492

Connections

Front panel inputs/outputs are:

• RF INPUT (50 Ω N connector) – Input for RF signals to 21 GHz. If input signal has a DC component, use a blocking capacitor
• CAL OUT (BNC connector) – Provides 100 MHz, –20 dBm signal and a comb of frequency markers 100 MHz apart
• 1ST LO OUTPUT (SMA connector) – Output of the 1st local oscillator, must be terminated into 50 Ω when not connected.
• 2ND LO OUTPUT (SMA connector) – Output of the 2nd local oscillator, must be terminated into 50 Ω when not connected.
• EXTERNAL MIXER RF INPUT (TNC connector, 50 Ω)
• Camera Power

Rear panel inputs/outputs are:

• PROBE POWER – Provides operating voltages (+5 V, -15 V, +15 V; 100 mA max each) for active probes
• HORIZ/TRIG (input, BNC) – In External Triggering mode, AC coupled input for trigger signals; when TIME/DIV selection is EXT, DC coupled input for horizontal sweep voltages
• MARKER/VIDEO (B053575+, output, BNC) – interfaces the 492/492P with a TV Sideband Adapter, such as the Tek 1405, so a marker from the adapter is displayed on the internal video. External video applied to this connector will also be displayed if pin 1 of the ACCESSORIES connector is grounded.
  • Opt. 42 replaces MARKER/VIDEO with 110 MHz IF (output, BNC) – 3 dB signal bandwidth ≥ 4.5 MHz
• EXT PRESELECTOR (B053574 and below) (output, BNC) – variable voltage (approx -0.2 V to +10 V) proportional to center frequency, for preselector bands of Opt. 01 instruments, to drive an external preselector
• HORIZ (output, BNC) – 0.5 V/div horizontal signal
• VERT (output, BNC) – Video signal with 0.5 V/Div
• PEN LIFT (output, BNC) – TTL compatible signal to lift the pen of a chart recorder during sweep retrace. In Opt. 42 instruments this port may also be used for inputting external video if pin 1 of the ACCESSORY connector is grounded.
• 10 MHz IF (output, BNC) – Output of the 10 MHz IF
• J104 ACCESSORY (B053575+ only), female DB25 connector – Provides bidirectional access to the instrument bus.
• IEEE STD 488 PORT GPIB interface – Added to all "P" suffixed instruments

Pictures

492

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  Internal top view

492A

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492BP

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492PGM

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