AN RF STEP ATTENUATOR

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This is low-cost, high performance RF Step Attenuator I have made myself and find that is very useful with any SDR receiver. Connected between connector from antenna cable and receiver input, I can manage antenna signal levels (depending of the frequency, various signals strenght and different ionospheric conditions) balancing them to the right amount at the receiver front end, in order to avoid any possible overload issues and achieve the best signal-to-noise ratio (SNR).

This is almost must-have tool especially with broadband SDR receivers, because they can "hear" whide frequency spectrum at their input and can be overload with some strong in-band or out-of-band signals, even if we don`t “see“ them.

An RF Step Attenuator has many other practical uses in ham radio lab.

The Attenuator consists simply of three resistive "Pi"-attenuator sections: 5 dB (I measured 5.5 dB) , 10 dB (I measured 10.5 dB) and 20 dB (I measured 22 dB). Each section consists of a DPDT mini switch and three 1/4W resistors. Combining all three switches, you can have 0, 5.5 dB, 10.5 dB, 16 dB, 22 dB, 27.5 dB, 32.5 dB and 38 dB.

All elements for this RF Step Attenuator cost not more than $10 USD. You need 9 resistors, 3 switches, 2 connectors and 1 metal box.

I have used 1590A type Aluminum Box, purchased from e-bay for less than $ 3 USD, and 3 SPDT switches for less than $1.5 USD..

Inside of the box:

Remember, too, that for the attenuation to be accurate, the input to the attenuator must be a 50 Ω source and the output line must be terminated in a 50 Ω load.

Practical usage:

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