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.

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

TOP OF PAGE