Thursday, 14 April 2016

Low cost spectrum analyser/ scanner with AirSpy and RTLSDR

Low cost spectrum analyser/scanner software for the Airspy and RTL-SDR

Introduction

It is not often I am amazed at new technology, especially for free, but the Spectrum Spy software, a spectrum analyser/scanner for the Airspy SDR, impressed me. It is a poor man's spectrum analyser.

However, it is preceded by at least two spectrum scanners for the RTL-SDR hardware; rtl_power and RTLSDR Scanner.

This post will compare the two devices and three software packages, scanning the entire FM band and the 100 MHz of the local TV band.

The software

The three programs all run under Windows, Windows 10 in my case. All three installed and ran without much difficulty.

Spectrum Spy is part of the SDR# software package. It is a separate program to SDR#, but in the same folder. Spectrum Spy has a spectrum and a waterfall. It updates every few milliseconds, depending on the span. Spectrum Spy only works with the US$199 Airspy. I have a V1 Airspy.

RTLSDR-Scanner is a stand-alone program; http://eartoearoak.com/software/rtlsdr-scanner. Use the "setup" version and it will download all the code it needs to install. No extra files are needed for the RTLSDR, provided its driver is installed. RTLSDR-Scanner is a single pass with spectrum but no waterfall.

Rtl_power is a small program that has both spectrum and waterfall. https://sourceforge.net/projects/guiforrtlpower/ Some additional RTLSDR files are needed to be copied to the program directory.

The hardware: apples and oranges

The Airspy and RTL-SDR both use the same tuner, but after that the Airspy is much more sophisticated. A significant difference is the frequency span, 10 MHz for Airspay and about 1.2 MHz for the RTL-SDR. The span makes a big difference to the scan rate of the scanner/analyser programs.

The question is whether the $20 RTL-SDR is useful as a scanner, compared to the Airspy.

FM band

A handy source of signals is the local FM band. The screen shots show how the three programs perform.

Spectrum Spy performs very well, showing a 20 MHz span. It shows both spectrum and waterfall. The waterfall is very useful for intermittent signals.


RTLSDR Scanner does a reasonable and useful job. The spectrum is comparable with Spectrum Spy. However, it only does a single scan and takes 20 seconds of so for the scan.


RTL_power had an indifferent result. The spectrum is quite different to the other two programs. While it does a continuous scan, the waterfall does not align with the spectrum.


TV band

The local DVB-T TV is in a 100 MHz band from 600 MHz. Displaying the TV stations is quite a test for a spectrum analyser.

The Spectrum Spy does a very good display in this demanding task.

The RTLSDR Scanner similarly does well in displaying the spectrum, although it takes quite some time to do the scan.


RTL_power does better with the TV than the FM, but is still not great.


Discussion

The Spectrum Spy program with the Airspy hardware does an awesome job comparable to some spectrum analysers, for low cost,

It would be ideal for doing repeater site surveys, especially with the waterfall as well as the spectrum.

RTLSDR Scanner could be used in a similar manner to Spectrum Spy, just taking longer with a single scan.

2 comments:

  1. You didn't comment on the dynamic range - it looks like the Airspy has a lower noise floor and larger dynamic range than the RTLSDR, as you expect from a 12bit ADC compared with 8bit. This would be very important in most spectrum analyser applications.

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    1. The post was a brief look at proof of concept software for the two devices, rather than the hardware.

      Yes, just as for SDR, the hardware specifications are important for use as a spectrum analyser. There has been much discussion of the devices' hardware in SDR applications.

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