1L40

Manuals – Specifications – Links – Pictures

The Tektronix 1L40 is a spectrum analyzer plug-in for 500-series scopes. It covers the frequency range from 1.5 GHz to 40 GHz using four different removable front-end mixers.

The 1L40 requires a 100 or 150 V sawtooth from the mainframe on a front-panel BNC input. The frequency axis display is back-to-front — lower frequencies are displayed to the right, higher frequencies to the left. This is because the 1^st LO is above the input signal frequency, yet the display shows the IF sweep from low to high left-to-right, so the displayed spectrum is inverted.

The 1L40 is also capable of displaying signals in its 1^st IF range of 150-250 MHz because the input is unfiltered, so everything passes straight through to the second mixer. In this case, however, the display is left-to-right.

Type 1L40 was produced for only 3 years, making it the shortest-lived letter-series plug-in.

Key Specifications

Center frequency	1.5 to 40 GHz
Dispersion	1 kHz/div to 10 MHz/div, 1−2−5
1st LO frequency	1.7 to 4.2 GHz
Resolution bandwidth	≤1 kHz to ≥100 kHz in 11 steps
IF attenuator	0 to 51 dB
Display dynamic range	≥40 dB in LOG mode

Links

Documents Referencing 1L40

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Patents that may apply to 1L40

Page	Title	Inventors	Filing date	Grant date	Links
Patent US 3321712A	Phase lock system for spectrum analyzer	Arnie Frisch • Gordon D. Long	1965-08-16	1967-05-23	Spectrum Analyzers • 1L20 • 1L30 • 1L40 • 7L18 • Sampling

Internals

The 1L40 shares the replaceable mixer input design with the 491. It came with a coaxial mixer, Tek part number 119-0096-00, which works up to 12.4 GHz using a 1N415D detector diode.

Higher frequencies are covered by three external waveguide mixers, connected via an 119-0104-00 adaptor:

• 119-0097-00: 12.4 GHz to 18 GHz
• 119-0098-00: 18 GHz to 26.5 GHz
• 119-0099-00: 26.5 GHz to 40 GHz

The 1^st LO consists of a Y1641 SHF triode with resonant cavities in cathode and anode circuits. The RF Center Freq control shortens or lengthens the cavities to vary the oscillator frequency between 1.7 and 4.2 GHz. A varactor provides additional VFC capability, allowing the oscillator to be phase locked to a reference frequency multiple. This is accomplished through a 2-diode sampling product detector driven by pulses on the order of 100 ps length, as explained in Patent US 3321712A. The pulses are generated from an internal 1 MHz or external 1-5 MHz reference frequency through an avalanche transistor and a step recovery diode.

1^st LO Harmonics up to ×10 are mixed with the RF input to produce the 1^st IF. After 280 MHz lowpass and 150-250 MHz bandpass filters, a 20 dB amplifier drives a mixer producing a 75 MHz 2^nd IF that goes into a switchable attenuator and a two-stage amplifier before it is mixed down to 5 MHz for the variable resolution amplifier.

Apart from the 1^st LO and a 12AU6 in the 5 MHz amplifier, the 1L40 is solid state.

Pictures

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  1L40 Front

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  Front view from catalog

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  Bent tooth on 1L40 tuning gear provides limit stop in both directions.

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  Front view

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  Threequarter view

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  Right side view. Note the housing for the removable input mixer at bottom left, and the tuned cavity for the 1st local oscillator at the top.

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  Left side view

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  Rear view. Note the selector switch to adapt the sweep input voltage to different models in the 500 series range.

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  Bottom view

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  Top view. Cavity for the 1st local oscillator is on the right, and the tuning mechanism is visible. IF filters and attenuators are in the can in the middle.

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  Input connector. This is the basic 1.5−12.4 GHz input, which can be removed and replaced with an extension cable to waveguide mixers for higher frequencies.

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  Closeup of RF centre frequency dial. Fundamental range is at the bottom with harmonics above.

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  Closeup of part of the dispersion range switch assembly. Note the two little fingers attached to the shaft which operate the toggle switch.

External Mixers and Adaptor

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  External Mixers and Adaptor

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  119-0097-00

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  119-0097-00

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  119-0098-00

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  119-0098-00

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  119-0099-00

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  119-0099-00

Measurement examples

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  1L40 in 535A mainframe tuned to 2100 MHz cellular band showing signals. 5 MHz/div dispersion.

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  Tuned to 2100 MHz cellular band (5 MHz/div dispersion) showing 3 G data downlinks from various operators. From the right: Orange, T-Mobile, Plus and Play. Photo taken in Warsaw, Poland, January 2018.

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  Signals displayed straight through the plugin's 150-250 MHz IF. Dispersion 5 MHz/div, centre frequency 200 MHz. The peak on the left is the local DAB radio multiplex on channel 6B, 183.648 MHz. The hump to the right of that is the local DVB-T multiplex 'Mux 8' on channel 7. Photo taken in Warsaw, Poland, January 2018.

Components

Some Parts Used in the 1L40