7L5

Manuals – Specifications – Links – Pictures

The Tektronix 7L5 is a low frequency (10 Hz – 5 MHz) spectrum analyzer plug-in for 7000-series scopes. It has built-in digital storage, so it will work fine in non-storage mainframes such as the large-screen 7603. It also features digital scale and marker level/frequency (6 digits) readout, and a "max hold" function.

According to the 070-2184-01 manual, instruments with a serial number below Β070000 are missing the B − (Save A) feature and the corresponding button on the front panel. The military version is called PL-1391/U and is also lacking the B − (Save A) feature.

Fendall Winston was Project Leader for the 7L5 and along with Craig Bryant and Steve Morton provided much of the electrical design. Bill Benedict and Don Kirkpatrick did the digital circuitry. Steve Skidmore coordinated mechanical design, with Carlos Beeck doing the optoelectronic switch-in-a-knob. Morris Engelson provided overall engineering direction for the program.

Key Specifications

Input frequency	10 Hz – 5 MHz
Drift	< 5 Hz/h
Resolution bandwidth	10 Hz – 30 kHz in ×3 / ×10 steps
Sweep rate	10 s/Div to 0.1 ms/Div in 1−2−5 sequence plus Auto
Residual FM	< 40 Hzp-p (< 1 Hz from 50 Hz/Div to 2 kHz/Div)
Outputs	Horizontal, Video, Calibrator
Input impedance	L1 input module: 50 Ω L2 input module: 75 Ω L3 input module: 50 Ω, 600 Ω or 1 MΩ selectable (75 Ω, 600 Ω or 1 MΩ for the L3-1)
Log Sweep Option	250 Hz to 222.25 kHz by digitally combining three decade sweeps (250 Hz—2.25 kHz, 2.25 kHz—22.25 kHz, 22.25 kHz—222.25 kHz), 2.5 s sweep time

Options

No.	Log sweep display	Tracking generator	LED Readout
21	•
25		•
28			•
30	•	•
31	•		•
32		•	•
33	•	•	•

Links

• 7L5 page @ amplifier.cd with internal photos
• 7L5 in operation @ youtube
• L1-GC

Documents Referencing 7L5

Document	Class	Title	Authors	Year	Links
Tekscope 1975 V7 N3.pdf	Article	A 5 MHz Digitally-Controlled Spectrum Analyzer		1975	7L5
TekWeek (partial) October 10, 1975.pdf	Article	Spectrum analyzers require high technology	Thor Hallen • Dave Friedley	1975	Spectrum Analyzers • Pentrix • 7L5 • 5L4 • 7L12 • 7L13 • 1401 • 491 • 1405 • 1502 • 1503
AX-3535.pdf	Application Note	Crystal Device Measurements Using the Spectrum Analyzer	Morris Engelson	1977	7L5 • 7L13 • TR502
Tekscope 1977 V9 N3.pdf	Article	Digital Storage for a Microwave Spectrum Analyzer	Dennis Smith • Don Kirkpatrick	1977	7L18 • 7L5 • 155-0157-00 • 155-0158-00
Tekscope 1977 V9 N2.pdf	Article	Measuring Harmonic Distortion with a Spectrum Analyzer	Ken Matheson	1977	FG504 • 7L5 • 5L4N
Tekscope 1978 V10 N3.pdf	Article	Spectrum Analyzer Applications in Baseband Measurements	Morris Engelson	1978	7L5 • L3 • 013-0182-00
AX-3406-1.pdf	Application Note	EMI Applications Using the Spectrum Analyzer	Morris Engelson	1979	7L5 • L1

In TekWeek 10 Oct 1975, Thor Hallen says

What is the Communications division doing to improve the reliability and field failure rates of high technology instruments such as the 7L5, 7L12 and 7L13 spectrumanalyzers?

Glad you asked! High technology instruments such as the spectrum analyzers you mentioned pose enormous problems in maintaining Tektronix standards for high reliability. Let’s consider the 7L5 for example. The 7L5 is the newest and most dense analyzer to date. It has approximately 2200 electrical parts packed into a two wide plug-in. (The 7L12 and 7L13 are slightly less dense.) With such a high parts population, a 0.5%/year failure rate for individual parts would be disastrous.

In order to deliver better reliability, extraordinary steps are being implemented within the manufacturing area. All benches have been covered with “pink poly” to make a static-free environment for the sensitive Metal Oxide Semiconductor (MOS) circuits of the 7L5. Assemblers and technicians are being trained in static handling of these devices.

The most embarrassing reliability problem that can occur is when the customer has an instrument failure within the first few hours of operation. To prevent this, the 7L5 goes through an extensive 7 day cycled burn-in. Each day the instrument is checked for electrical performance. Any failures are repaired and the burn-in is continued until the instrument has completed the 7 days. Any failures in the last two days will cause the burn-in to continue until the instrument displays two consecutive days without a failure.

Along with burn-in and special handling, extensive effort is given to analysis of field and plant failures for reliability problems.

In answer to your question, we have only discussed the 7L5, but the 7L12 and 7L13 receive similar treatment. There is no final solution to improved reliability. As instruments increase in complexity and reliability, challenge increases proportionately.

Prices

Year	1976	1980	1988
Catalog price	$4,500	$7,075	$12,500
In 2023 Dollars	$24,300	$26,400	$32,400

According to an internal memo, in 1979 annual sales were estimated at 454 units.

Pictures

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  7L5 Opt. 33 in 7633 mainframe

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  7L5 Opt. 32

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  7L5 Opt. 25

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  7L5 in 7844

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  7L5 Opt. 25 without B - (Save A)

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  Front Panel of 7L5

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  Back side of 7L5 front panel

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  Complete IF Assembly of 7L5

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  Complete IF Assembly of 7L5

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  RF Module (Vertical Control Board and 1st LO assembly) of 7L5

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  Sweep board of 7L5

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  7L5 A and B oscillator control board front side

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  7L5 A and B oscillator control board back side

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  Front side of Tune Reference A board

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  Back side of Tune Reference A board

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  Front side of Tune Reference B board

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  Back side of Tune Reference B board

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  Front side of A oscillator board

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  Back side of A oscillator board

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  Front side of B oscillator board

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  Back side of B oscillator board

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  Later revision of 7L5 digital storage and average board - front side

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  Later revision of 7L5 digital storage and average board - back side

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  Tektronix 7L5 Transverse Interface Board

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  Tektronix 7L5 Transverse Interface Board

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  Top view of L3 plugin assembly

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  Bottom view of L3 plugin assembly

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  7L5 prepared for servicing the sweep and reference boards

7L5 Opt.25 tracking generator plug-in

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For internal pictures see the repair section.