Using your SDRPlay RSPx as a Spectrum Analyzer for testing

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someYguy
Posts: 49
Joined: Sun Apr 10, 2016 7:12 pm

Using your SDRPlay RSPx as a Spectrum Analyzer for testing

Postby someYguy » Sun Jan 01, 2017 8:44 pm

Hi everyone!

As an extension of my post about using your RSPx receiver as a scalar network analyzer (See that here: http://www.sdrplay.com/community/viewtopic.php?f=7&t=1562).

This post will show that the RSPx receivers can indeed be used to accurately measure signal amplitude, frequency, and quality.

For the measurements shown here, the following equipment was used:

SDRPlay RSP1 SDR Receiver

SDRSharp SDR software, build 1361

Hewlett-Packard model HP-8656B RF Signal Generator

Reference Level = -30 dbm

Test Frequency = 10 mhz

=====================

First picture shows an AM modulated carrier with an amplitude of -30dbm:

Image

The signal is modulated with a standard 1khz tone at 30%. Notice that the sidebands are clearly visible.

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someYguy
Posts: 49
Joined: Sun Apr 10, 2016 7:12 pm

Re: Using your SDRPlay RSPx as a Spectrum Analyzer for testing

Postby someYguy » Sun Jan 01, 2017 8:59 pm

Next picture shows the same signal, but I have reduced the amplitude from the signal generator to -70 dbm. Nothing else was changed. Notice that the display does show the correct amplitude:

Image

After initial amplitude calibration, the RSPx and software will be accurate and linear throughout the measurement range. Amplitude calibration is achieved via the gain slider within the RSPx Device Control Panel, with AGC and LNA both turned OFF. Simply calibrate to a constant signal of known amplitude as I've done here.

One more picture of the 1khz AM signal at -100 dbm:

Image

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someYguy
Posts: 49
Joined: Sun Apr 10, 2016 7:12 pm

Re: Using your SDRPlay RSPx as a Spectrum Analyzer for testing

Postby someYguy » Sun Jan 01, 2017 9:21 pm

Next picture shows the same AM signal but I have narrowed the span to about 4khz total, using the "Zoom" slider control in SDRSharp. In previous photos, span was at approximately 20khz.

Image

This allows viewing of details for signal analysis such as distortion products etc.

Next, we show an FM signal which is modulated at 3 khz deviation using a 1 khz tone. Amplitude is -70dbm:

Image

=================

So as can be seen from these experiments, these receivers can very well be used for accurate signal testing and analysis as well as for testing of antennas, filters, and other devices.

Although absolute accuracy will not be as good as a dedicated spectrum analyzer, it certainly is more than adequate for most testing needs from what I can tell.

What is really needed is a good software program for these types of receivers which has features for these purposes such as markers, delta functions, large and dedicated amplitude & frequency readouts, etc.

Have fun!

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VE4NSA
Posts: 1
Joined: Sat Jan 07, 2017 2:35 pm

Re: Using your SDRPlay RSPx as a Spectrum Analyzer for testing

Postby VE4NSA » Sat Jan 07, 2017 2:38 pm

Did you connect the RF generator output directly to the SDRPlay antenna input?
Last edited by VE4NSA on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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someYguy
Posts: 49
Joined: Sun Apr 10, 2016 7:12 pm

Re: Using your SDRPlay RSPx as a Spectrum Analyzer for testing

Postby someYguy » Sat Jan 07, 2017 5:48 pm

Yes, the signal generator output is directly connected to the RSPx antenna input. Maximum input level is about -30dbm before artifacts start showing. An external step attenuator can be used for higher levels if needed.

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