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The Tektronix Type 280 Trigger Countdown Unit takes in a signal with repetition rate 50MHz and 5GHz
{{Instrument Sidebar
and puts out a pulse train with repetition rate in the 15 to 45 MHz range. 
|manufacturer=Tektronix
The main purpose of the 280 is to extend the
|model=280
frequency range of the the trigger circuitry in sampling scopes.  For example, consider a scope
|class=Accessory
with a [[3T77]] and a [[3S2]] with [[S2]] sampling heads.  The S2 has response to at least 4GHz
|series=
but the [[3T77]] is only rated to trigger up to 300MHz, so the setup cannot, for example, be used
|summary=Trigger Countdown Unit
to observe a 2GHz sinewave.  By using a Type 280, the 2GHz sinewave can be fed to the Type 280,
|image=Tek_type_280_1.jpg
which will produce 15 to 45 MHz pulses whose leading edges are synchronized with the a particular
|caption=Tek Type 280
trigger point in the 2GHz signal.  These lower frequency pulses can be fed to the 3T77, which
|introduced=1963
will easily trigger.  The main concern with a setup like this is jitter.  The 3T77 is rated at
|discontinued=(?)
50ps jitter.  The presence of the 280 does nothing to help the jitter of 3T77, so that becomes
|designers=
the limiting factor.  Assuming that for a clear display, the triggering jitter must be less than
|manuals=
10% of the period of the observed signal, this gives a minimum signal period of 500ps (2GHz). 
* [[Media:070-350.pdf|Tektronix 280 Manual]]
So the 280 extends the top of frequency range of the system from 300MHz to 2GHz.  This was very
}}
useful with a [[661]] with a [[4S2|4S2A]] and a [[5T1]].  The 5T1's maximum triggering frequency is
The '''Tektronix Type 280 Trigger Countdown Unit''' takes in a signal with repetition rate between 50 MHz and 5 GHz, and puts out a pulse train with repetition rate in the 15 to 45 MHz range whose leading edges are synchronized with a particular trigger point in the input signal.
1GHz and it has 30ps of jitter.  The 4S2A's frequency response extends to 3.5GHz.  Without the
280, the maximum sinewave frequency that can be observed is 1GHz.  With the 280 it is 3.5GHz.
Later timing plug-ins like the [[5T3]] include built-in synchronizing circuits that eliminate
the need for the countdown units such as the 280.


The main purpose of the 280 is to extend the frequency range of the trigger circuitry in sampling scopes.
For example, consider a scope with a [[3T77]] and a [[3S2]] with [[S-2]] sampling heads.
The S-2 has response to at least 4 GHz but the [[3T77]] is only rated to trigger up to 300 MHz, so the setup cannot, for example, be used to observe a 2 GHz sinewave. 


* [http://bama.edebris.com/download/tek/280/Tek%20280.pdf Tektronix 280 Manual (PDF)]
By using a Type 280, the 2 GHz sinewave can be fed to the Type 280, which will produce 15 to 45 MHz pulses that can be fed to the 3T77, which will easily trigger.


The main concern with a setup like this is jitter.  The 3T77 is rated at 50 ps jitter.
The presence of the 280 does nothing to help the jitter of 3T77, so that becomes the limiting factor.
Assuming that for a clear display, the triggering jitter must be less than 10% of the period of the observed signal, this gives a minimum signal period of 500 ps (2 GHz). 
The 280 thus extends the top of frequency range of the system from 300 MHz to 2 GHz.
This was very useful with a [[661]] with a [[4S2|4S2A]] and a [[5T1]] as the 5T1's maximum triggering frequency is 1 GHz and it has 30 ps of jitter but the 4S2A's frequency response extends to 3.5 GHz.
Without the 280, the maximum sinewave frequency that can be observed is 1 GHz; with the 280 it is 3.5 GHz.
Later timing plug-ins like the [[5T3]] include built-in synchronizing circuits that eliminate the need for the countdown units such as the 280. 
Signal connections on the 280 use [[GR-874 connector]]s. The trigger circuit is built around a [[152-0099-00|50 mA (152-099)]] [[tunnel diode]].
==Pictures==


<gallery>
<gallery>
Image:Tek 280.jpg
Tek 280.jpg|Photo
Image:Tek 280 schem.png
Tek 280 schem.png|Schematic
Tek type 280 1.jpg
Tek type 280 2.jpg
Tek type 280 3.jpg
Tek type 280 4.jpg
Tek type 280 5.jpg
Tek type 280 6.jpg
</gallery>
</gallery>
{{Parts|280}}
[[Category:GR874]]

Latest revision as of 02:07, 13 November 2022

Tektronix 280
Trigger Countdown Unit
Tek Type 280

Produced from 1963 to (?)

Manuals
(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix Type 280 Trigger Countdown Unit takes in a signal with repetition rate between 50 MHz and 5 GHz, and puts out a pulse train with repetition rate in the 15 to 45 MHz range whose leading edges are synchronized with a particular trigger point in the input signal.

The main purpose of the 280 is to extend the frequency range of the trigger circuitry in sampling scopes. For example, consider a scope with a 3T77 and a 3S2 with S-2 sampling heads. The S-2 has response to at least 4 GHz but the 3T77 is only rated to trigger up to 300 MHz, so the setup cannot, for example, be used to observe a 2 GHz sinewave.

By using a Type 280, the 2 GHz sinewave can be fed to the Type 280, which will produce 15 to 45 MHz pulses that can be fed to the 3T77, which will easily trigger.

The main concern with a setup like this is jitter. The 3T77 is rated at 50 ps jitter. The presence of the 280 does nothing to help the jitter of 3T77, so that becomes the limiting factor. Assuming that for a clear display, the triggering jitter must be less than 10% of the period of the observed signal, this gives a minimum signal period of 500 ps (2 GHz).

The 280 thus extends the top of frequency range of the system from 300 MHz to 2 GHz. This was very useful with a 661 with a 4S2A and a 5T1 as the 5T1's maximum triggering frequency is 1 GHz and it has 30 ps of jitter but the 4S2A's frequency response extends to 3.5 GHz. Without the 280, the maximum sinewave frequency that can be observed is 1 GHz; with the 280 it is 3.5 GHz.

Later timing plug-ins like the 5T3 include built-in synchronizing circuits that eliminate the need for the countdown units such as the 280.

Signal connections on the 280 use GR-874 connectors. The trigger circuit is built around a 50 mA (152-099) tunnel diode.

Pictures

  • Photo

    Photo

  • Schematic

    Schematic


Some Parts Used in the 280

Part Part Number(s) Class Description Used in
120-0290-00 120-0290-00 Discrete component power transformer 280
SMTD907 152-0275-00 Discrete component 50 mA, 5 pF germanium tunnel diode 280 • 661
TD1081 152-0099-00 • 152-0334-00 Discrete component 50 mA, 6 pF germanium tunnel diode 280 • 661 • 017-0086-00
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