Using the Airspy HF+ as a Power Meter By Calibrating it with a Resistor

Over on YouTube, Leif (SM5BSZ) has uploaded a video where he shows how the Airspy HF+ can be used as an accurate power meter for RF signals. Leif notes that if the noise figure (NF) or minimum discernible signal (MDS) of an SDR is known, then it is possible to use that SDR as a power meter by calibrating it with a resistor (dummy load) at room temperature. To determine power levels Leif uses the signal diagnostics plugin which is built into SDR#. He writes in the video description:

When the noise figure (NF) or minimum discernible signal (MDS) of a software defined radio (SDR) is known we can use that radio as a power meter just by calibrating it on a room temperature resistor. Here the Airspy HF+ is used to demonstrate the principles. Note that MDS depends on the temperature. Manufacturer data is for a warmed up unit. Cold units have significantly lower MDS. Note the observations on bad adapters and attenuators towards the end of the video. One conclusion is that the HF+ is EXCELLENT in keeping common mode currents on the USB as well as on the antenna cable outside. They do not enter the receiver provided that the nut holding the SMA connector is firmly tightened.


In another video Leif also tests out a pre-production version of a HF+ preselector currently being designed by Youssef (designer of the HF+) by measuring the filter responses.



  1. re-flash

    You should download the latest firmware and read the README.TXT file inside the archive (The very bottom of the page):

    Since you are on the oldest firmware (which is 15 version old at time of posting this reply) you will need to follow the “Recovery Procedure” for the very first firmware upgrade.

    Oh, and there is a forum that you could search, or post on, if you run into a problem I think all the possible problems that could be encountered have been encountered so far, but just in case..

  2. Robert

    I know that this is off subject , but the video makes it eraser to explain the problem . In the top video at the start of it you can see in the source box the options that are their for HF+ dongle use , HF threshold , HF preamp , and HF Att and they work . The firmware is R1.7.0 I am talking about SDR Sharp software . Well when I got my Airspy HF+ about two months ago I down loaded the SDRshrap software from Airspy’s website . In the source box the firmware reads R1.00.00 . and those options don’t work . Now I don’t know if R1.00.00 the newer or older than R1.0.7.0 . Now what do I need to get to get those controls to work .

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