[time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)
Robert LaJeunesse
rlajeunesse at sbcglobal.net
Mon Dec 12 19:25:14 UTC 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 (?)
https://picasaweb.google.com/109928236040342205185/FE5680A#5685304143859526258
-John Beale
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