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7L12: Difference between revisions
circuit description
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Late models had LED reference level readout. | 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 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. | The Tek catalogs suggested the [[7603]] Opt.06 or [[7613]] Opt.06 as suitable mainframes. | ||
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}} | }} | ||
{{EndSpecs}} | {{EndSpecs}} | ||
==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 1<sup>st</sup> mixer. The 1<sup>st</sup> LO is a YIG oscillator running at 2.095 GHz to 3.9 GHz, resulting in a 2.095 GHz 1<sup>st</sup> IF. This 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 2<sup>nd</sup> mixer. The 2<sup>nd</sup> LO oscillates at 2.2 GHz (variable by +/- 1 MHz) for a 2<sup>nd</sup> IF of 105 MHz, which is amplified, then filtered in a 3-stage helical filter with 3 MHz bandwidth before passing through a 3<sup>rd</sup> 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 1<sup>st</sup> LO at spans of 0.1 MHz/Div and less, tying its frequency to a multiple of 2.21 MHz using an avalanche pulse shaper driven diode sampler as a mixer. In phase lock, the 2<sup>nd</sup> LO is swept instead of the 1<sup>st</sup>. The fine frequency control is only operational in phase lock mode. | |||
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== | ==Prices== | ||
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|- | |- | ||
! Year | ! Year | ||
! | ! 1971 | ||
! 1980 | |||
! 1984 | |||
! 1988 | |||
|- | |||
! Catalog price | |||
| align="right" | $4,850 | |||
| align="right" | $6,500 | |||
| align="right" | $10,250 | |||
| align="right" | $12,500 | |||
|- | |||
! 2015 value | ! 2015 value | ||
| align="right" | $28,100 | | align="right" | $28,100 | ||
| align="right" | $18,760 | | align="right" | $18,760 | ||
| align="right" | $23,460 | | align="right" | $23,460 | ||
| align="right" | $24,800 | | align="right" | $24,800 | ||
|- | |- | ||
|} | |} | ||
==Links== | ==Links== | ||
* [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_special/spectrumanalyzer_7L12.htm Tek 7L12 @ amplifier.cd] | * [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_special/spectrumanalyzer_7L12.htm Tek 7L12 @ amplifier.cd] | ||
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File:Tek-7l12-top.jpg | Top view | File:Tek-7l12-top.jpg | Top view | ||
File:Tek-7l12-right.jpg | Right side | File:Tek-7l12-right.jpg | Right side | ||
Tek-712-right-front.jpg | Right side toward front. The 1<sup>st</sup> mixer (bottom left) and 1<sup>st</sup> LO (large cylindrical can) are visible. | |||
File:Tek-7l12-bottom.jpg | Bottom view | File:Tek-7l12-bottom.jpg | Bottom view | ||
File:Tek-7l12-bottom-front.jpg | Bottom front | File:Tek-7l12-bottom-front.jpg | Bottom front | ||
File:Tek-7l12-bottom-center.jpg | Bottom center | File:Tek-7l12-bottom-center.jpg | Bottom center. The 3-stage 2<sup>nd</sup> IF 105 MHz helical filter is visible in the middle (black cylinders). | ||
File:Tek-7l12-top-front.jpg | Top front | File:Tek-7l12-top-front.jpg | Top front | ||
File:Two 7L12s.jpg | later and early model side by side | File:Two 7L12s.jpg | later and early model side by side | ||