Performance testing of Software Defined Radios

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Performance testing of Software Defined Radios

Do SDRs perform better than conventional Superhet architecture radios? A big problem is that many of the traditionally used tests, which compare radios on league tables and in reviews, are not very relevant to SDRs due to fundamental differences in technology.

A very good article on this topic by Andrew Barron ZL3DW

Performance testing of Software Defined Radios

We already published a post on the sensitivity of the Quadrus SDR here:

http://spectrafold.com/quadrus/digitizer-hardware/sdr-receiver-sensitivity-test/

The published results are:

SSB -111 dBm at 10 dB S+N/N with 2.1 kHz bandwidth

CW  -119 dBm at 10 dB S+N/N with 400 Hz bandwidth

According to Andrew:

MDS (Minimum Discernible Signal)

MDS is a measurement of how sensitive the receiver is. It represents the weakest signal you can hear. You need it to be good if you want to hear very weak signals on a quiet band, for example when sunspots are poor or the band is closing. If the band is noisy the noise level coming in the antenna port will often be higher than the MDS so sensitivity is not as relevant.

In the test a signal is input to the receiver and the MDS is the input signal level when it shows as 3dB above the receiver noise floor. The MDS is better if the bandwidth of the receiver is reduced because a narrow bandwidth allows less noise in. So it is usually measured using a typical CW bandwidth of 500Hz and using a typical SSB bandwidth of 2.4kHz. It is normally checked on several bands as well. In most SDR receivers especially direct sampling (digital down conversion DDC) receivers you would expect the same performance on all bands. When you compare results relating to different radios, check that no attenuators or preamplifiers are in use. Most SDR receivers have an MDS better than -125dBm in 500Hz bandwidth and better than -115dBm in 2.4kHz bandwidth. Excellent receivers can achieve an MDS better than -130dBm in 500Hz bandwidth and better than    -120dBm in 2.4kHz bandwidth. SDRs with 8bit analog to digital conversion (ADC) will probably not be able to achieve that level of performance because of limited dynamic range.

It is not easy to compare the results, because we’ve measured in 400 Hz / 2.1 kHz bandwidth instead of 500 Hz / 2.4 kHz, and we’ve measured a 10 dB signal above the noise floor instead of 3 dB. However, we can do a very simple calculation of adding 7 dB to the 3/10 dB measurement level difference.

So our performance testing comparable to this reference article is:

SSB -118 dBm at 3 dB S+N/N with 2.1 kHz bandwidth

CW  -126 dBm at 3 dB S+N/N with 400 Hz bandwidth

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