7L13

The Tektronix 7L13 is a 1 kHz to 1.8 GHz Spectrum Analyzer plug-in for 7000-series scopes. From 1977 on, a modified version with coverage up to 2.5 GHz was available upon request (no official option listed in the catalog).

It is similar to the 7L12 but occupies three module bays, adds a marker function, offers resolution bandwidth down to 30 Hz, and improves sensitivity by 10 dB. It also displays the center frequency in the CRT readout as well as on a LED display.

The TR502 tracking generator is designed to work with the 7L13 up to 1.8 GHz.

Key Specifications

Input frequency	100 kHz – 1.8 GHz (modified version up to 2.5 GHz)
Span	200 Hz/Div – 100 MHz/Div
Sweep	1 μs/Div to 10 s/Div (1−2−5), manual, external
Resolution bandwidth	30 Hz – 3 MHz in decade steps
Sensitivity	−128 dBm at 300 Hz to −80 dBm at 3 MHz
Vertical scale	10 dB/Div, 2 dB/Div or linear
Reference level	−110 dBm – +30 dBm in 10 dB steps
Video filters	30 kHz, 300 Hz or 10 Hz
Features	Automatic phase lock CRT readout of center frequency UNCAL indicator built-in calibrator 50 MHz, −30 dBm Base line clipper

Links

• Tektronix 7L13 @ barrytech.com
• Tektronix 7L13 @ radiomuseum.org

Prices

Year	1974	1976	1980
Catalog price	$6,500	$7,500	$10,500
2020 Dollars	$34,100	$34,100	$33,000

Internals

The input signal passes a 0 to 60 dB step attenuator, a 1.8 GHz low-pass filter, and a 3 dB isolation pad before the 1^st mixer, with a 1^st LO frequency between 2.095 GHz and 3.895 GHz. At spans of 50 kHz/Div and below, the 1^st LO (a YIG oscillator) is fixed (stabilized by a PLL) and the 2^nd LO is swept.

The 1^st IF filter is 10 MHz wide, centered at 2.095 GHz. With a 2^nd LO at 2.2 GHz, the signal is mixed to a 105 MHz IF, amplified, filtered again (105±1.5 MHz) and mixed down to 10 MHz (3^rd LO at 95 MHz).

At the 10 MHz 3^rd IF, resolution filters (300 kHz L/C, 30 kHz, 3 kHz or 300 Hz crystal filters) can be selected. The detector (discrete log amplifier) and video filters follow.

The digital frequency readout is a DVM (Fairchild 3814) working off the the YIG oscillator control voltage, not a frequency counter, which is why it needs to be calibrated before use.

Custom integrated circuits used: 155-0035-00 quad opamp, 155-0042-02 Miller integrator, 155-0056-00 sweep control, 155-0088-00 legend generator.

Pictures

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Display examples

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  7L13 displaying a POCSAG FSK signal at 162 MHz (variable persistence storage on a 7623)

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