10 dB Power Attenuators

Attenuator of 10 dBThis attenuator is a Pi-type, 50 ohm attenuator for 10 dB. It is designed for 50 ohms and must be terminated with 50 ohms, to give the right attenuation. This basic Pi-type 10 dB attenuator uses two resistors of 95.25 ohm and one of 71.15 ohm. Don't panic after reading those values. The value of 96.25 ohm can be formed with 100 ohm and 2700 in parallel. The value of 71.15 ohm can be made by 82 ohm and 560 ohm in parallel. This basic 10 dB attenuator can be built with 6 resistors from the E12-series and can dissipate an input power of 0.5 W, when built with resistors of 1/4 W.

Power attenuators
Power distribution of a 10 dB AttenuatorA 10 dB power attenuattor with an input power of 5 watts, will divide the power by 10, so the output power will be 500 mW. The attenuator must dissipate 4.5 W. Most of the power is dissipate by R1, which dissipates 2.6 W. R2 will dissipate 1.6 W and R3 only 0.26 W. By using several resistors in parallel, it is possible to build attenuators for any input power. The more resistors are used, the higher the maximum input power of the attenuator. By using good available (induction free) resistors of 1/4 W, you don't need "unavailable" precicion, power resistors, to build an 10 dB power attenuator.

10 dB power attenuators
The 10 dB attenuators shown here are all built with good available 1/4 W resistors of the E12-series. Each of the 4 attenuators is designed for a diffenent value of input power. They cover the power spectrum from 500 mW to 5 watts.
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Attenuator of 10 dB for 500 mW 
The basic 10 dB attenuator consist of 6 resistors and is good for an (continues) input power of 500 mW.
Attenuator of 10 dB for 1.6 W
Built with 9 resistors the attenuator is suitable for 1.6 W
Attenuator of 10 dB for 2.6 W
With 13 resistors the attenuator is good for 2.8 W (or 5.6 W in CW)
Attenuator of 10 dB for 5 W
Built with a total of 20 inexpensive resistors the attenuator can handle a continues input power of 5 W.  Don't worry about number of resistors. In the attenuator for an input power of 5 watts, 11 resistors in parallel are needed, to form R1. Don't make a PCB, but just simply twist the leads together. This 11 resistors of 1/4 will take about the same space as 3 or 4 resistors of 1 watt. The attenuators can be switched on or off. With the switch in the lower position the signal will go through the attenuator.

Tip: Please add a switch to the all attenuators, even when you use only one attenuator. It is very important to have the possibility to switch the attenuators "on" or "off" at any moment, for example for tuning with full power.

Don't worry about the 5% accuracy of the resistors.
It is OK, if the resistors have an accuracy of 5 %. The real accuracy will be much better than 5%. I built my attenuator of 10 dB and an attenuator of 20 dB, using resistorswith an accuracy of 5% that were at hand. The accuracy of the compound resistors R1, R2 and R3 is much better than 5%.


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