[time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)

Robert LaJeunesse rlajeunesse at sbcglobal.net
Mon Dec 12 14:25:14 EST 2011

Was the probe grounded using a spring clip off the probe tip, hitting the 
nearest ground that is tied directly to the 9572? If not, the waveform captured 
is not the waveform present during operation. Also, using a 10pF probe on a 2ns 
risetime signal is quite a heavy load / impedance mismatch. I've used 100:1 low 
capacitance probes (Zin = 5000 Ohms, Cin = 2pF or less) to mitigate that problem 
at less cost than a good FET probe. I also suspect the filter impedance is not 
constant versus frequency, leading to additional distortion of the square wave.
Bob LaJeunesse

From: beale <beale at bealecorner.com>
To: time-nuts at febo.com
Sent: Mon, December 12, 2011 1:29:24 PM
Subject: [time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)

... A 200 MHz Rigol scope reads a risetime of 2 ns on CPLD pin 49, but the 
waveform looks so noisy and odd (see below), maybe I would be better off just 
squaring up the output sine.  ...maybe if pin 49 was disconnected from the sine 
output filter, it would be more square (?)


-John Beale

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