Using your SDRPlay RSPx as a Spectrum Analyzer for testing

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someYguy
Posts: 113
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: 113
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: 113
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: 113
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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JJ_in_TN
Posts: 23
Joined: Wed Jun 07, 2017 10:04 pm

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

Postby JJ_in_TN » Tue Mar 19, 2019 3:51 pm

With that version of SDR# getting a bit long in the tooth and all the improvements to SDRuno and other compatible software, is there any reason to use that old version of SDR# in 2019? Can SDR# do anything the others can't?

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someYguy
Posts: 113
Joined: Sun Apr 10, 2016 7:12 pm

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

Postby someYguy » Sun Mar 24, 2019 4:08 am

JJ_in_TN wrote:With that version of SDR# getting a bit long in the tooth and all the improvements to SDRuno and other compatible software, is there any reason to use that old version of SDR# in 2019? Can SDR# do anything the others can't?


Yes, there is good reason IMO to use this older version of SDR# for this. First, no other compatible software gives you as much control over the FFT display parameters - even the new (and wonderful, thank you Steve) SAS Spectrum Analyzer program.

With SDR#, there is very fine control over spectrum display attack & decay times, resolution, Waterfall attack & decay, and spectrum speed. These controls allow much finer and higher resolution and averaging of the display than is available with other programs and the use of adjustable sliders rather than only predefined steps from a dropdown for attack & decay times is much better. Also, the zoom slider in SDR# is very fast and highly responsive. I can set the resolution to a mid value and then use the zoom slider and get sufficient resolution so that I can clearly see two signals just 5-10hz apart. Much more use to me than the predefined zoom ranges in other programs.

Two caveats however - Later versions of SDR# have gone to a different type of spectrum display and it looks like they apply some type of real-time averaging to the waveform. SDR Console v3.xx also does this. The result is that the trace is just a bit fuzzy and not as clear or defined as that in SDR# v1361.

Also, the level display is not calibrated so you must calibrate it by using the gain slider in the SDRPlay device control panel for the frequency range of interest. I made a chart after initial calibration using a calibrated HP 8656B signal generator and so my setup is quite accurate for level measurements.

So those are my reasons for using that old version, anyway. Also, older SDR# is portable in that you can put the whole folder of it on a memory stick and run from most Windows machines without need to install.

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sdrom33
Posts: 118
Joined: Sun Dec 09, 2018 4:38 pm

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

Postby sdrom33 » Mon Mar 25, 2019 3:34 pm

Hi someYguy, I would like to use RSPX you mention, but do not know where to download. Can you help? I have the rsp1a.

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someYguy
Posts: 113
Joined: Sun Apr 10, 2016 7:12 pm

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

Postby someYguy » Tue Mar 26, 2019 3:44 am

sdrom33 wrote:Hi someYguy, I would like to use RSPX you mention, but do not know where to download. Can you help? I have the rsp1a.


Sure thing. See here:http://www.sdrplay.com/community/viewtopic.php?t=248

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sdrom33
Posts: 118
Joined: Sun Dec 09, 2018 4:38 pm

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

Postby sdrom33 » Wed Mar 27, 2019 7:47 pm

Very many thanks, SomeYguy!! Very useful info.

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