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Tektronix 3L5
1 MHz Spectrum Analyzer
Tektronix 3L5 Spectrum Analyzer

Compatible with 560-series scopes

Produced from 1967 to (?)

Manuals – Specifications – Links – Pictures

The Tektronix 3L5 is a 50 Hz — 1 MHz spectrum analyzer plug-in for 560-series scopes.

It is very similar to the 1L5 and can be used to measure the spectrum of signals.

In conjunction with the 015-0107-00 "Swept Frequency Generator" (tracking generator), the 3L5 can also be used to make scalar frequency response measurements. A video filter switch was added to the later SNs (1971 Catalog). The 3L5 is based on the swept-frontend design, where the first local Oscillator is swept for the spectrum scan. It is a full semiconductor design except for the final output amplifier, which uses a 8416 vacuum tube.

75 Ω Version

There is also a 75 Ω version of the 3L5. Its input is on the rear, via a coaxial connector. A lever on the front panel switches between two frequency ranges:

  • 10 kHz - 1 MHz
  • 18.010 MHz - 19 MHz

Timebase Support

3L5 requires a timebase plug-in in the horizontal compartment to operate. Timebase plug-in units with serial no listed and below require modification 040-0413-00 to provide the sweep signal to the 3L5 (To pin 18 of the plug-in connector).

Time Base SN#
2B67 15180
3B1 4040
3B3 4270
3B4 740

Key Specifications

Center Frequency Range 50 Hz to 990 kHz
Dispersion Range 10 Hz to 100 kHz
Input Impedance ≈ 1 MΩ // 30 pF
Input Voltage Max. 300 V (DC + peak AC)
Vertical Resolution Video - .1 v/div to 100 v/div, LIN - .001 V to 2V RMS
Internal Cal Signal 5 kHz ±1%
First LO Out ≥1 MHz (Sweep), ≥1 Vp-p into ≥1 kΩ
Recorder Out 5 mV to 15 mV into 600Ω
Weight ≈6 pounds


1 MΩ version

75 Ω version