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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.
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RESISTORS
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REQUIRED
R
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Ra
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Rb
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PARALLEL
VALUE
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ERROR
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R1
& 3
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61.111
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91
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180
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60.443
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1.09%
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R2
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247.5
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3300
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270
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249.580
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-0.84%
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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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last revised 12 March 2022
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