1401: Difference between revisions
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[[Image:Tek1401a-front.jpg|thumb| | [[Image:Tek1401a-front.jpg|thumb|400px|right|Tektronix 1401A Spectrum Analyzer Module]] | ||
The Tektronix 1401A is a | The '''Tektronix 1401A''' is a spectrum analyzer front-end covering the frequency range | ||
of 1 MHz to 500 MHz | of 1 MHz to 500 MHz, designed to be used with an external oscilloscope, typically a [[323]], | ||
[[324]] or [[326]]. It has internal rechargable NiCd batteries and can also operate | [[324]] or [[326]]. It has internal rechargable NiCd batteries and can also operate | ||
from AC power (using an unusual power cord) or external DC from | from AC power (using an unusual power cord) or external DC from 6 V to 16 V. | ||
There appear to be two variants of the 1401A, both the manual and | There appear to be two variants of the 1401A, both the manual and | ||
catalog specify the resolution bandwidth selector as 1000, 100 and 3 | catalog specify the resolution bandwidth selector as 1000, 100 and 3 kHz, | ||
but the later versions are 100, 100, and 10 | but the later versions are 100, 100, and 10 kHz. There is also a 1401A-1 | ||
which has a 75 | which has a 75 Ω input impedance. The predecessor 1401 did not have | ||
the BNC "cal output" or "cal on" pushbutton switch. | the BNC "cal output" or "cal on" pushbutton switch. | ||
The 1401A is designed to be used with an oscilloscope with 10 horizontal | The 1401A is designed to be used with an oscilloscope with 10 horizontal | ||
divisions and 6 vertical divisions. Tektronix says it is compatible with any | divisions and 6 vertical divisions. Tektronix says it is compatible with any | ||
oscilloscope having 0. | oscilloscope having 0.5 V/div horizontal deflection factor and 1.2 V full screen | ||
vertical deflection. Note that most full sized Tektronix | vertical deflection. Note that most full sized Tektronix | ||
oscilloscopes have 8 vertical divisions so use care when doing the | oscilloscopes have 8 vertical divisions so use care when doing the | ||
initial setup and reading the scale in dBm. Also note the lack of a Z-axis | initial setup and reading the scale in dBm. Also note the lack of a Z-axis | ||
output. | output. | ||
==Internals== | |||
Operation is typical of a swept front end analyzer. The input is attenuated and | Operation is typical of a swept front end analyzer. The input is attenuated and | ||
low-pass filtered to 500 MHz. It is then mixed with the first LO, a | low-pass filtered to 500 MHz. It is then mixed with the first LO, a varactor | ||
tuned oscillator that can sweep 695 MHz to 1195 MHz. The first mixer is a double | tuned oscillator that can sweep 695 MHz to 1195 MHz. The first mixer is a double | ||
balanced, four diode star. The signal is DC coupled to this mixer. The manual is | balanced, four diode star. The signal is DC coupled to this mixer. The manual is | ||
| Line 33: | Line 35: | ||
detected and send to the video out. | detected and send to the video out. | ||
==Repair issues== | |||
See TekScope January 1972 pages 14-15 for some servicing notes that | See TekScope January 1972 pages 14-15 for some servicing notes that | ||
Tek wrote after the manual was published. [http://w140.com/tekwiki/images/d/d6/Tek1401a-tekscopes.pdf Service Note] | Tek wrote after the manual was published. [http://w140.com/tekwiki/images/d/d6/Tek1401a-tekscopes.pdf Service Note] | ||
There is one tunnel diode found in the external trigger circuit. | There is one tunnel diode found in the external trigger circuit. | ||
It is a 152-0402-00, a | It is a 152-0402-00, a 2 mA, 25 pF tunnel diode in a DO-17 package. | ||
It | It is only used when the external trigger input is connected. | ||
There is one Tektronix custom IC, 155-0042-02, listed as a Miller Integrator. | There is one Tektronix custom IC, [[155-0042-02]], listed as a Miller Integrator. | ||
It is used to generate the sweep ramp voltage. The package is a | It is used to generate the sweep ramp voltage. The package is a 10 pin metal can. | ||
10 pin metal can. | |||
The input attenuator is a fairly custom part due to the IF gain pot | The input attenuator is a fairly custom part due to the IF gain pot | ||
| Line 48: | Line 50: | ||
attenuator is easy after removing it from the 1401A. Note that the | attenuator is easy after removing it from the 1401A. Note that the | ||
IF gain pot is removed via two allen setscrews. To bench test the | IF gain pot is removed via two allen setscrews. To bench test the | ||
attenuator with DC, use a 50 | attenuator with DC, use a 50 Ω terminator on SMA input and connect | ||
the output SMA to an ohm meter. Each of the seven steps should read | the output SMA to an ohm meter. Each of the seven steps should read | ||
around 50 | around 50 Ω. The contacts on the ceramic attenuator elements | ||
can wear, they can be repaired with silver solder. Before reassembly, | can wear, they can be repaired with silver solder. Before reassembly, | ||
remove the two SMA housings to avoid damaging the contacts and remove | remove the two SMA housings to avoid damaging the contacts and remove | ||
| Line 57: | Line 59: | ||
has been screwed together. | has been screwed together. | ||
==Pictures== | |||
<gallery> | <gallery> | ||
File:Tek1401a-front.jpg|Front panel | |||
File:tek1401a-top.jpg|Top PCB: IF board | |||
File:tek1401a-bottom.jpg|Bottom PCBs:gate/cal, power supply | |||
File:tek1401a-batterypcb.jpg|PCB on the battery pack | |||
File:Tek1401a-logamp.jpg|Cartoon in schematic diagram. Log Amp. | |||
</gallery> | </gallery> | ||