7L12

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The Tektronix 7L12 is a 1.8 GHz Spectrum Analyzer plug-in for 7000-series scopes. It is a double-width plugin to be installed in the right vertical and left (or only) horizontal bay.

Early models had a mechanical reference level readout. Later, front panel outputs for 1st and 2nd LO were added to allow connecting a TR501 or TR502 tracking generator. Late models had LED reference level readout.

The 7L12 does not have the UNCAL indicator typical for spectrum analyzers that alerts the operator when the sweep speed is too fast for the given resolution. The manual advises to use the variable control to reduce sweep speed until the signal amplitudes don't change.

The Tek catalogs suggested the 7603 Opt.06 or 7613 Opt.06 as suitable mainframes.

Specifications

Input frequency 100 kHz – 1.8 GHz (Opt.39: 2.5 GHz)
Span 500 Hz/Div – 100 MHz/Div
Sweep 1 μs/Div to 5 ms/Div (1-2-5)
Resolution bandwidth 300 Hz – 3 MHz in decade steps
Sensitivity −115 dBm at 300 Hz
Vertical scale 10 dB/Div, 2 dB/Div or linear
Reference level −100 dBm – +30 dBm
Video filters 30 kHz, 300 Hz or 3 Hz
Features
  • Automatic phase lock
  • Built-in calibrator
  • Base line clipper

Internals

The 7L12 is a traditional triple-mixing spectrum analyzer design. The input signal runs through a step attenuator (0 to 60 dB in 10 dB steps), a 1.8 GHz low-pass filter and a 3 dB pad (to isolate the mixer from LPF reflections) to a 1st mixer. The 1st LO is a YIG oscillator running at 2.095 GHz to 3.9 GHz, resulting in a 2.095 GHz 1st IF.

The 1st IF passes through a "traveling wave damper" (isolator), a 2.2 GHz LPF and a 10 MHz wide 2.095 GHz bandpass filter before reaching the 2nd mixer. The 2nd LO oscillates at 2.2 GHz (variable by ±1 MHz) for a 2nd IF of 105 MHz, which is amplified, then filtered in a 3-stage helical filter with 3 MHz bandwidth before passing through a 3rd mixer to the final 10 MHz IF, variable resolution filters, and post-resolution amplifier to the "Function IF amplifier" that implements the linear or logarithmic detector.

A phase lock circuit controls the 1st LO at spans of 0.1 MHz/Div and less, tying its frequency to a multiple of 2.21 MHz using a diode sampler employed as a mixer. The sampling gate is driven by an avalanche pulser. In phase lock, the 2nd LO is swept instead of the 1st. The fine frequency control is only operational in phase lock mode, one of the key limitations of this design.

The 7L12 includes a standard sweep circuit built around the 155-0056-00 Sweep Control (U1140) and 155-0042-02 (U1160) Miller Integrator custom ICs. The 7L12 also uses the TEK-custom quad opamp 155-0035-00 in several places.

Prices

Year 1971 1974 1976 1980 1984 1988
Catalog price $4,850 $4,850 $4,995 $6,500 $10,250 $12,500
2020 Dollars $31,000 $25,500 $22,700 $20,400 $25,500 $27,350

Mods

Links

Pictures

Custom ICs used in the 7L12

Page Class Manufacturer Model Part nos Description Designers Used in
155-0035-00 Monolithic integrated circuit Tektronix M053B 155-0035-00 155-0116-00 quad op-amp Mike Metcalf 3110 3S7 3T7 4010 4011 4012 4013 7L5 7L12 7L13 7L14 7L18 7S11 7T11 7S12 S-6 1461 4602 P7001 613 653
155-0042-02 Monolithic integrated circuit Tektronix M018 155-0042-00 155-0042-01 155-0042-02 155-0042-03 Miller integrator 5B42 7B53A 7S14 7L12 7L13 RG501 Telequipment D63 Telequipment DM63
155-0056-00 Monolithic integrated circuit Tektronix M042E 155-0056-00 sweep control Val Garuts 26G1 26G2 26G3 314 4701 5B10N 5B12N 7L5 7L12 7L13 7L14 7L18 7S14 5S14N RG501 Telequipment D63 Telequipment DM63