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Re: [TenTec] OT: Scopes

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] OT: Scopes
From: Ken Brown <ken.d.brown@hawaiiantel.net>
Reply-to: ken.d.brown@hawaiiantel.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 20 Feb 2012 10:55:38 -1000
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>

> As someone else said, instrumentation scopes include a front panel Cal 
> test point.  This is a source of a known voltage and frequency square 
> wave train, which can be used to the input of each vertical channel to 
> test calibration.  If it is as marked on the Cal point, the vertical 
> channel is OK for amplitude.  Look at the squareness of the wave for 
> frequency response.
You can also use this square wave generator to check and adjust the 
compensation capacitor in the probe to match the scope input. What you 
are doing is getting the capacitive voltage division ratio equal to the 
resistive voltage division ratio. Some capacitance is unavoidable, so 
the 10X probe is not simply 9 Megohm resistor in series with the 1 
Megohm o'scope input to make a DC voltage divider, it also has a 
specific (adjustable) capacitance to make a proper AC voltage divider 
with the scopes input capacitance. When adjusted properly the leading 
edge of the square wave will not overshoot or undershoot, and the top 
platform of the square wave will be flat and horizontal, not sloping up 
or down.

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