Monday, July 1, 2019

41 dB step attenuator kit from QRPKits

Last week I ordered a step attenuator kit from QRPKits and received it 4 days later. This afternoon I spent 45 minutes putting it together and am happy with the result and overall quality of the kit.

Two years ago I built the "Damn Reliable Attenuator" from Kees K5BCQ and have used it periodically. So why another step attenuator?

While the K5BCQ attenuator is fine for the job I bought it to do - attenuating the signal of various QRPp WSPR transmitters - its 1-watt resistors limit its use for power levels of above 3 or 4 watts.

I noticed this when I wanted to feed the output of my old KX2 into the RSPduo (operating in spectrum analyzer mode) and, with 5 watts in, the attenuator's resistors became quite warm after just a few seconds.

The attenuator from QRPKits uses 2-watt resistors to form its pads and is rated for 5 watts continuous and 10 watts intermittent. This makes it more suitable for QRP (as opposed to QRPp) applications.

With the RSPduo now able to function as a spectrum analyzer, the need for a suitable attenuator has now been met. FWIW, the maximum continuous input to the RSPduo is 1 mW; 10 mW intermittent. 37dB of attenuation from a 5 watt QRP rig takes the power down to 1 mW and, with this new attenuator, will do so without overheating the resistors.

I also like the bypass switch which gives the ability to switch in or out any attenuation level with a single switch.

In addition to being a worthy piece of test equipment this would make a great "first" kit for a new builder. And for anyone who has a compatible SDR receiver from SDRPlay and desires to use spectrum analysis software with it, this new step attenuator is more than worth its $25 price.





  1. Good evening John, the step attenuators are a very cool thing to have and I purchased and built the Hendricks 41dB step attenuator some years ago. I really enjoyed and it and when the solar cycle was not peaking but just so so I was able to use the attenuator to drop my K3's output to the milli watts and make some amazing miles per watt contacts into Europe.

    1. Hi Mike - I'll probably do the same thing with the U3S. One other good thing about an attenuator for this use is that you don't need a QRPp wattmeter to adjust your output to a QRPp level. Just put 5 measured watts into the attenuator, dial in your level of attenuation and calculate the output - no WM-2 needed to obtain a known output.

      73 - John