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.
.


.


.

 .
.
.

2 comments:

  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.
    73,
    Mike
    VE3WDM

    ReplyDelete
    Replies
    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

      Delete