280: Difference between revisions

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The Tektronix Type 280 Trigger Countdown Unit takes in a signal with repetition rate 50MHz and 5GHz
The '''Tektronix Type 280 Trigger Countdown Unit''' takes in a signal with repetition rate 50 MHz and 5 GHz and puts out a pulse train with repetition rate in the 15 to 45 MHz range.   
and puts out a pulse train with repetition rate in the 15 to 45 MHz range.   
 
The main purpose of the 280 is to extend the
The main purpose of the 280 is to extend the frequency range of the the trigger circuitry in sampling scopes.  For example, consider a scope with a [[3T77]] and a [[3S2]] with [[S2]] sampling heads.  The S2 has response to at least 4 GHz
frequency range of the the trigger circuitry in sampling scopes.  For example, consider a scope
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.   
with a [[3T77]] and a [[3S2]] with [[S2]] sampling heads.  The S2 has response to at least 4GHz
 
but the [[3T77]] is only rated to trigger up to 300MHz, so the setup cannot, for example, be used
By using a Type 280, the 2 GHz sinewave can be fed to the Type 280,  
to observe a 2GHz sinewave.  By using a Type 280, the 2GHz sinewave can be fed to the Type 280,  
which will produce 15 to 45 MHz pulses whose leading edges are synchronized with the a particular trigger point in the 2 GHz signal.  These lower frequency pulses can be fed to the 3T77, which will easily trigger.   
which will produce 15 to 45 MHz pulses whose leading edges are synchronized with the a particular
 
trigger point in the 2GHz signal.  These lower frequency pulses can be fed to the 3T77, which
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
will easily trigger.  The main concern with a setup like this is jitter.  The 3T77 is rated at  
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).   
50ps 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
So the 280 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]].   
10% of the period of the observed signal, this gives a minimum signal period of 500ps (2GHz).   
 
So the 280 extends the top of frequency range of the system from 300MHz to 2GHz.  This was very
The 5T1's maximum triggering frequency is 1 GHz and it has 30 ps of jitter.  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.
useful with a [[661]] with a [[4S2|4S2A]] and a [[5T1]].  The 5T1's maximum triggering frequency is
 
1GHz and it has 30ps of jitter.  The 4S2A's frequency response extends to 3.5GHz.  Without the
Later timing plug-ins like the [[5T3]] include built-in synchronizing circuits that eliminate the need for the countdown units such as the 280.   
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.   




* [http://bama.edebris.com/download/tek/280/Tek%20280.pdf Tektronix 280 Manual (PDF)]
* [http://bama.edebris.com/download/tek/280/Tek%20280.pdf Tektronix 280 Manual (PDF)]


==Pictures==


<gallery>
<gallery>
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Image:Tek 280 schem.png|Schematic
Image:Tek 280 schem.png|Schematic
</gallery>
</gallery>
[[Category:Introduced in 1963]]

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