Magic Signal to Noise (SNR)

18 Feb 2022


Thanks to several people who have taken it upon themselves to aggregate and report the data, along with the ability of the KiwiSDR to measure and report signal to noise ratios, many people with KiwiSDRs are competing with their stations to achive the highest SNR.

Looking at the data, it seems than an average station might achieve an SNR of around 25 dB, a good station perhaps 30 dB, and superlative installations over 35 dB.

Imagine then my surprise when habitually checking the list, I found a station, IW2NKE, reporting a SNR of 50 dB. Of course, I had to investigate this anomaly. Looking at the IW2NKE waterfall, I was stunned to see very strong signals on the regular amateur radio and broadcast bands, and nothing in betweee, no noise, QRM, or static crashes.

IW2NKE SDR Waterfall Zoom

However, upon further investigation, I found out that this installation seems to be different that many others: Selecting a frequency in the amateur or broadcast bands works fine, but selecting an “odd” frequency outside of those bands yields nothing, no audio.

I’m not sure how or if this is done with the KiwiSDR software, but from a signal processing point of view, it seems clear that in generating a signal to noise ratio, if you select portions of the spectrum where signals exist, and ignore portions where only noise exists, then your signal to noise ratio will improve.

Addendum: From the KiwiSDR manual:

  • Type, and creating blocked (masked) frequencies/bands The different types simply select a color for the marker label to help differentiate them.

There is one important exception. The menu entry “masked” is used to create a blocked frequency or frequency range where no reception is possible (i.e. no audio is heard and no waterfall appears). This is useful when the Kiwi owner/admin wants to prevent users from listening to certain frequencies/ranges possibly tying up channels for long periods of time (e.g. Skyking HFGCS EAM broadcasts, CB band). The passband area, either the default for the selected mode or the custom passband field, defines the masked frequency boundaries. To define a large masked band area see this Kiwi forum post.