View source for 3L5

{{Plugin Sidebar 
|manufacturer=Tektronix 
|series=560-series scopes 
|type=3L5 
|summary=50 Hz - 1 MHz Spectrum Analyzer Plug-In
|image=Tek 3L5 front2.jpeg 
|caption=Tektronix 3L5 Spectrum Analyzer 
|introduced=1967
|discontinued=(?)
manuals=
* [[Media:070-0630-01.pdf|Tektronix 3L5 Manual]]
* [[Media:Tek 3l5 fcp aug 1967.pdf|Tektronix 3L5 Factory Calibration Procedure, August 1967]]
}}
The '''Tektronix 3L5''' is a 50 Hz − 1 MHz spectrum analyzer plug-in for [[560-series scopes]]. It is very similar to the [[1L5]].

In conjunction with the [[015-0107-00]] Swept Frequency Converter (tracking generator), the 3L5 can also be used to make scalar frequency response measurements.

{{BeginSpecs}}
{{Spec | Center Frequency    | 50 Hz to 990 kHz }}
{{Spec | Dispersion          | 10 Hz to 100 kHz }}
{{Spec | Input Impedance     | 1 MΩ // 30 pF }}
{{Spec | Input Voltage       | Max. 300 V (DC + peak AC) }}
{{Spec | Vertical Resolution | Video: 100 mV/div to 100 V/div, LIN: 1 mV to 2 V<sub>RMS</sub> }}
{{Spec | Internal Cal Signal | 5 kHz ±1% }}
{{Spec | First LO Out        | ≥1 MHz (Sweep), ≥1 V<sub>p-p</sub> into ≥1 kΩ }}
{{Spec | Recorder Out        | 5 mV to 15 mV into 600 Ω }}
{{Spec | Weight              | 2.7 kg / 6 lbs }}
{{EndSpecs}} 

A video filter switch was added to the later SNs (1971 Catalog). 

==Internals==
The 3L5 is a full semiconductor design except for the final output amplifier, which uses a [[8416]] vacuum tube.  The circuit is based on the swept-frontend design, i.e. the first local oscillator is swept for the spectrum scan. 

=== 75 Ω Version ===
There is also a 75 Ω version of the 3L5.   Its input is on the rear, via a coaxial connector.
A lever on the front panel switches between two frequency ranges:
* 10 kHz − 1 MHz
* 18.010 MHz − 19 MHz

===Timebase Support===
The 3L5 requires a timebase plug-in in the horizontal compartment to operate. 

Timebase plug-in units with serial numbers listed below require modification [[040-0413-00]] to provide the sweep signal to the 3L5 (To pin 18 of the [[560_Series_plug-in_interface|plug-in connector]]).

{| class="wikitable"
|-
! Time Base
! SN# 
|-
| [[2B67]] || <15180
|-
| [[3B1]]  || <4040
|-
| [[3B3]]  || <4270
|-
| [[3B4]]  || <740
|}

==Pictures==
'''1 MΩ version'''
<gallery>
Tek 3L5 front2.jpeg | Front
Tek 3L5 left2.jpeg  | Left
Tek 3L5 right2.jpeg | Right
Image:Tek 3l5 front.jpg | 1 MΩ Version 
Tek_3L5_LateSN.jpeg | 1 MΩ Later Version with Video Filter Switch
3L5_LHS.jpeg | LHS
3L5_RHS.jpeg | RHS
3L5_Top.jpeg | Top
3L5_Bottom.jpeg | Bottom
3L5_Filter-Chassis_1.jpeg|Internals - 3 MHz Filter, 2nd LO (3.1 MHz) and 2nd Mixer. 
3L5_Filter-Chassis_2.jpeg|Internals - 3 MHz Filter, 2nd LO (3.1 MHz) and 2nd Mixer. 
158-0022-00_1.jpeg | Internals - 100 kHz Crystal from Variable Resolution Amp [[158-0022-00]]
158-0022-00_2.jpeg | Internals - 100 kHz crystal from Variable Resolution Amp [[158-0022-00]]
</gallery>

'''75 Ω version'''
<gallery>
3l5 18mhz fr2.JPG   | 75 Ω Version of 3L5, Front
Tek 3l5 75ohm 1.jpg | 75 Ω Version, Front/Top
Tek 3l5 75ohm 4.jpg | 75 Ω Version, Left
Tek 3l5 75ohm 5.jpg | 75 Ω Version, Top
Tek 3l5 75ohm 6.jpg | 75 Ω Version, Bottom/Left
3l5 18mhz l.JPG     | 75 Ω Version
3l5 18mhz l2.JPG    | 75 Ω Version
3l5 18mhz rr2.JPG   | 75 Ω Version, Back
</gallery>

==Components==
{{Parts|3L5}}

[[Category:Spectrum analyzers]]
[[Category:560 series plugins]]