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Re: RSP Spectrum analyser software available shortly

Posted: Wed May 09, 2018 8:00 pm
by SteveAndrew
Hi John

For sweep widths greater than 10MHz I'm pretty well doing the same thing as your Signal Hound SA. Adding two or more segments together is the only way wide sweeps can be achieved. For a 10MHZ chunk, the usable bandwidth is around 8MHz, with quit heavy attenuation at the band edges. In order to avoid this attenuation, I'm tuning in steps of 5MHZ. I could tune in steps of around 8Mhz, which is the maximum usable bandwidth, but at 5MHZ, the maths works out quiet nicely and gives a nice flat response that does not include a series of dips where a signal of interest would be quiet heavily attenuated.

The problem I have is when the RSP crosses band boundaries at 60, 120, 250, 420 and 1000MHz. There are quiet large jumps in amplitude as the radio is tuned across the boundaries, and it looks like the gain reduction needs to be adjusted for each band. I have tried doing this but it doesn't appear to work as I expected. I seem to be getting some instability at this point, with each band section jumping up and down quiet a bit. Also, signals randomly appear in the wrong segment, indicating a tuning problem. Where the problem seems to be is that while a change of frequency within a band segment can take anything from 0.5 to around 15ms, a frequency step across the band boundary can take up to 150ms. Currently there seems to be no way of knowing when the newly tuned frequency has settled. SDRplay have been most supportive and we are going to be discussing this, and other issues some time in the next couple of days.

I'm getting a similar instability problem with the DC spike, so performing a null scan to establish a baseline will not cure the problem. Having said that, I think the spike problem is due to me doing something wrong somewhere as the DC correction system seems to work very well with SRDuno. I'm going to change the system so it uses a low IF instead of a zero IF at narrower sweep widths, that will eliminate the spike problem completely. I'm not sure if I'll get that done in time for the first aplha release though.

When playing around with the tracking generator side of the equation, using both broadband noise, or a DDS, I was using a similar system in order to establish a flat response across a given sweep width. Having said that, the noise generator seems to give a fairly flat output, making a baseline calibration fairly trouble-free.

I think Phil's idea regarding the RSP generating it's own tracking signal is interesting, but as I'm not familiar with the radio's architecture I can't say much about it. It would be nice if it could be done though.

All in all, I think the problems I'm experiencing are largely of my own making and I'm sure they can be sorted out.

73's - Steve

Re: RSP Spectrum analyser software available shortly

Posted: Wed May 09, 2018 8:29 pm
by 9a4db
Great news Steve, keeping my fingers crossed :)

Regarding possible tracking option, you may consider some kind of external communication
over the ports like Osmo GSM stack is doing / Not sure about OS platform , W10 or some Linux or both.
Can be great possibility to use signal source like ERASynth or run another HW like LimeSDR
on signal source side. Just somehow must be documented.

GL de 9A4DB Djani

2 x SDRPlay RSP1
2 x LimeSDR
1 x ERASynth+
1 x Agilent E7495B

Re: RSP Spectrum analyser software available shortly

Posted: Thu May 10, 2018 11:03 am
by tardivat
A spectrum analyzer is most useful when it has as many types of markers as possible. Especially delta markers.

Since the RSP is mainly a HF receiver, a calibrated 9khz EMC filter with Quasi peak detector would be very useful. Likewise RMS Average.A DbUv amplitude scale would also be useful. The new CISPR detectors like CISPR Average and CISPR RMS would make the RSP popular as a pre-compliance EMC receiver for devlopment work.

Other detectors like maximum peak, rms, average, auto peak and minimum would be very useful

The ability to set a automatic calibration factor like antenna factor or gain offset would also be useful specially if it automatically compensated for.
Peak hold for various bandwidth settings like Linrad would be useful for ham radio use.

I look forward to further developments that makes the RSP a general purpose engineering and RF engineering tool

Re: RSP Spectrum analyser software available shortly

Posted: Thu May 10, 2018 11:39 pm
by SteveAndrew
Currently I'm only interfacing to the SDRplay series of SDR radios. I don't have plans at the moment to interface to other external hardware, but that may be something to consider for the future.

uv/dBuv scale is on the ToDo list. Gain offset is already incorporated, although it's currently a fixed figure for the selected input. it wouldn't take much to expand on that to take allow calibration tables for antenna factors to be used so that the offset tracks with frequency. There are a pair of delta cursors/markers available. More could be added but may not be included in the alpha or beta versions. Peak hold is already included, as is the ability to hold or snapshot a trace on-screen.

All suggestions have been added to an ever-expanding ToDo list and will be considered. Due to the way the software has evolved, I would really like to re-write a lot of it, but the alpha version will make a good test bed and help shake out possible bugs in each of the main code modules.

As always, many thanks for your thoughts and suggestions.

73's - Steve

Re: RSP Spectrum analyser software available shortly

Posted: Fri May 11, 2018 9:52 am
by tardivat
Hi Steve

I would not bother with the Quasi peak or other EMC detectors if it does not have an associated CISPR defined filter like 9khz for HF. The Quasi peak readings will be have to calculated for whatever bandwidth you define to have much meaning in the real world of standards.

See this link on the the CISPR 16-1-1 definition of a EMC receiver.

Anyway I look forward to your future developments. I would suggest that a EMC spectrum analyzer as pre-compliance tool would be very popular only because Measuring receivers and EMI Measurement kits for spectrum analysers are so expensive. Something like the RSP with appropriate spectrum analyser software would be good enough for pre-compliance work that most design engineers do. It also might be very popular as a university EMC teaching tool.

All the best.

Re: RSP Spectrum analyser software available shortly

Posted: Sun May 13, 2018 2:44 am
by Phillip
Please forgive my ignorance. Am I correct in assuming a minor amount of hardware (other than the RSP) will be needed for this tool? If so, what will I need? I'd like to have things ready. :-)


Re: RSP Spectrum analyser software available shortly

Posted: Sun May 13, 2018 10:06 pm
by SteveAndrew
Hi Phil

Nothing much is needed. I think most people are going to be using a cheap broadband noise generator and a return-loss bridge. You can get both of these off EBay for a few dollars. I've included links to a couple I found. Shop around, prices vary. The noise generator shown usually runs off 12V, and is known to get quiet warm. I run mine off 5V. It seems to perform quiet happily and runs cool. At 5v, output is only around -50dBm though. I've not actually checked the output at 12V, but it should be a lot higher. ... SwKGxaudkn ... SwnHZYQH0u

73's - Steve

Re: RSP Spectrum analyser software available shortly

Posted: Mon May 14, 2018 2:19 pm
by arvopl
There is this $15 kit that combines the noise source and the bridge:

Re: RSP Spectrum analyser software available shortly

Posted: Wed May 16, 2018 2:12 am
Steve, where will we be able to download the software, and how will we know it's available for download?

Re: RSP Spectrum analyser software available shortly

Posted: Wed May 16, 2018 6:30 am
by SteveAndrew

As mentioned, I'll post a message here, and on the Facebook group. I've not yet finalised a download site.

The analyser is about ready to launch, but be aware it will be very much an alpha release, and still has several small problems that need to be addressed. I need to discuss a couple with SDRplay. As they are pretty busy with Daytona and a new product launch at the moment, I'll keep out of their way until the dust has settled somewhat, and probably contact them early next week.

I still have to prepare an installation package, some basic documentation, along with list of known problems as well. If all goes well, then it should be available for download in around a week from now - but once again I repeat, it will only be an alpha release. not a beta.

73's - Steve