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STANDARD ATTENUATOR

40dB standard attenuator. 


In addition to a step attenuator a large fixed value attenuator can be useful for receiver sensitivity evaluations and amplifier gain evaluations etc..

 

The 40dB fixed attenuator is derived from two 20dB Pi attenuation pads as shown in Fig 1 schematic below. The use of two pads instead of just one 40dB pad was chosen as it can be difficult to achieve a large dB step change due to r.f. leakage. The resistance values required were derived from paralleled on hand resistors in stock.  All resistors are of a 5% tolerance however should be adequate for the intended purpose.  

 

Fig 1  Standard Attenuator schematic. The broken lines represent PCB pad shielding.

 

RESISTORS REQUIRED  R Ra Rb PARALLEL VALUE ERROR
R1 & 3 61.111 91 180 60.443 1.09%
R2 247.5 3300 270 249.580 -0.84%

 

Fig 2  Resistor combinations to achieve required attenuation pad resistor values.

 

 

 

Photo 1  View of the assembly of the Standard Attenuator PCB ground for screen and component attachment.

 

Photo 2  View of the assembled Standard Attenuator.

 

Photo 3  Front view of the assembled Standard Attenuator.  

 

 

Related projects:

 

Also see step attenuator project: Sep Attenuator

 

 

References:

 

Pi & Tee Network Resistive Attenuation Calculator

http://n9zia.ampr.org/att_pad.cgi

 

PI Attenuator Calculator

http://www.random-science-tools.com/electronics/PI_attenuator.html

 

The Pi-pad Attenuator - Equations

http://www.electronics-tutorials.ws/attenuators/pi-pad-attenuator.htm

 

Fixed Pi and Tee Attenuators - Equations

http://www.rfcafe.com/references/electrical/attenuators.htm

 

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Page last revised 05 December 2015  
 

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