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Message ID: 4883     Entry time: Sat Jun 25 04:40:43 2011
Author: Suresh 
Type: Update 
Category: ASC 
Subject: WFS1 Transimpedance measurement 

WFS1 Transimpedance

The attached plots show the location of the ~29.5 MHz pole and the 59 MHz notch for each quadrant of the WFS1 Sensor head.

 

WFS1 Pole (MHz) Z(Ohms) Notch (MHz) Z(Ohms)
Q1 28.89 598 60.38 0.83
Q2 29.20 513 57.70 0.57
Q3 29.63 681 59.63 0.89
Q4 28.89 609 58.13 0.78

 

As may be seen from the above table, these frequencies will need to be adjusted in some cases.

From the plots we can see that, when there is no attenuation set on the attenuator AT65-0263 (ref D990249-A),  the MAX4107  oscillations are seen in Q2,Q3,Q4 quadrants at around 200 MHz.  

Rana suggested, from his previous encounter with this circuit, that the solution is to remove the second MAX4106 and the attenuator on the RF line to avoid this oscillation.

 

WFS1_transimpedance.pdf

A look at the circuit board shows that some of the inductors have not been mounted.  That explains the presence of only one notch though the schematic shows two. 

P6250224.JPG         P6250223.JPG

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