Using the tinySA to measure attenuation

Frequency selections in 'CAL' mode

Eric Kaashoek made a posting to the tinySA Group.io a few days ago, noting that the tinySA (and Ultra) can be used to check/verify the attenuation of various passive components.

Normally, a nanoVNA would be used for such a task, but if you don't have one, there's an easy and accurate way to use the tinySA.

As most know, the tinySA is both a spectrum analyzer and a signal generator. But the process described by Eric uses both of these functions simultaneously by enabling the tinySA's 'Calibration' mode.

In this mode, the device can be selected to output a test signal on one of 7 discrete frequencies.

That signal is sent from the CAL output and fed back into the RF input jack. The signal and its power level can then be observed by placing the tinySA into 'Spectrum Analyzer' mode and selecting the appropriate START/STOP frequencies:

 

Make note of the power level, then place your DUT in series with the tinySA's two jacks and then read the power level again. The difference between the two power levels is the attenuation of the DUT at that particular test frequency.

 

This also demonstrates the benefit of expressing power levels in terms of dBm: dBm (a power level) and dB (an attenuation/amplification level) can be added and subtracted directly. In this case -56 dBm - (-36) dBm = 20 dB, the attenuation I have dialed in.

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PS

The step attenuator used here is from HecKits - many, many degrees better than the plasticky toy attenuators offered by QRPGuys, etc. My build of this kit is here.

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