IQ Correction

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Stan
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IQ Correction

Postby Stan » Fri May 08, 2015 10:45 pm

I have noticed when using SDRplay with either SDR# or SDR-Conslole, the IQ blip doesn't get suppressed like it does when I'm using a RTL-820t dongle.
These are the only two software packages that I currently use. Is this a software issue or a hardware issue?
Thanks,
Stan
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TyTanYGraig
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Joined: Wed Jan 07, 2015 1:58 pm

Re: IQ Correction

Postby TyTanYGraig » Sat May 09, 2015 6:32 am

Try using the ExtIO plugin. The latest versions of SDR# don't work correctly as far as I/Q correction with the older custom plugin.

Cheers

TyTanYGraig
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jon
Posts: 303
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Re: IQ Correction

Postby jon » Sat May 09, 2015 8:17 am

That's right, the latest version of the actual SDR# software no longer supports I/Q correction - we hope to update our guides to steer people to using EXTIO instead. Many thanks to all who post their observations on the forum. We at SDRplay do read them all and will use them to improve our support in the future.
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DaveB
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Re: IQ Correction

Postby DaveB » Sat May 09, 2015 10:08 am

Using the Ext_IO works - the SDRPlay team sorted this a little while back and I had been running it by simply copying the HDSDR EXTIO dll across. The current page on the web-site has version 2.0 of the SDR# plugin which implements this plus improvements to the GUI.

However - note for the SDRPlay team. The instructions don't actually tell you that you are looking for the EXT_IO.SDRPlay.dll in the source dropdown menu, nor that there isn't a line in the SDR# lugins.xml file. Although an SDRPlay line is installed.

I'm sure the installation instructions will be updated soon - but as far as my experience goes once you have finished installing the plugin just look for the highlighted entry in the source dropdown menu that you can see shown below.

SDR# dropdown source menu.jpg
SDR# dropdown source menu.jpg (27.85 KiB) Viewed 6617 times


You should then see the gain and phase numbers constantly change when you are tuned to a station. It improves the image rejection by around 15-20dB.

As to the question is it a software or hardware issue the answer is that is a hardware issue that requires a software solution. The hardware 'issue' is that the SDR Play product - in common with a number of other poducts is based on Quadrature switching detectors which produce two signals about the centre frequency. One you want and the other you don't want. The I and Q signals are added together 90 degrees out of phase to cancel out one of the signals - but it's not perfect. A software solution was developed a few years ago which improved the rejection of the unwanted signal and appears to be much improved since the early days. SDR# does the correction automatically. HDSDR allows you to manually fine tune the I/Q channels to get a much more precise balance. Once you have the I/Q correction optimised you shouldn't have any image problems.

The RTL dongle - apart from anything else it has a low dynamic range so you can't get a strong enough signal for the problem to manifest itself and as far as I understand it the R820T based dongles have a different architecture anyway.

Rgds

David
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jon
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Re: IQ Correction

Postby jon » Sat May 09, 2015 12:06 pm

Thanks Dave :-)
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Stan
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Re: IQ Correction

Postby Stan » Sat May 09, 2015 8:51 pm

Thanks Dave.
I've been using the V2 for a bit now and even posted a suggestion on some improvements.
I guess in SDRconsole the SDRplay isn't quite optimized to get rid of the IQ imbalance.
I first became aware of the problem when I clicked on any of the WWV time stations in SDRconsole. I got either no signal or one that was quite small as to be almost not there. If I moved the frequency so it wasn't dead center the signal would be quite loud. Now with a sightly better understanding of what is going on, I guess it's just the way SDRplay is implemented in SDRconsole.

Stan...
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NN4F
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Location: Ridgeville, SC
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Re: IQ Correction

Postby NN4F » Mon May 11, 2015 4:14 pm

I've been emailing with Simon Brown, he's revisiting the SDRplay set up in SDR-Radio, and this should be fixed, also allowing access to the LNA gain setting...

Paul - NN4F
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--
Paul Jones - NN4F, Charleston SC
http://www.facebook.com/groups/SDRPlay

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Stan
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Re: IQ Correction

Postby Stan » Tue May 12, 2015 4:33 pm

NN4F wrote:I've been emailing with Simon Brown, he's revisiting the SDRplay set up in SDR-Radio, and this should be fixed, also allowing access to the LNA gain setting...

Paul - NN4F

Thanks, for the info.
I also saw his video of the new software, looks quite impressive.
So far I'm quite happy with my SDRplay. On SW it gives my Icom R75 a good run. Prob not hard to do as it's quite old tech, but still a solid Radio.
Stan
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bristolpirates
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Joined: Fri May 15, 2015 2:49 pm

Re: IQ Correction

Postby bristolpirates » Fri May 15, 2015 3:25 pm

Hi. I'm a brand new SDRPlay owner. I've been using the RTL dongles by NooElec for the past couple of years.

I was wondering, with the SDRPlay, should the IQ spike drop completely into the noise or is it normal for there to still be a little bit of a spike?

Also, is this IQ problem connected to the images I'm seeing in the 2m band where a signal will appear on one side of the screen and be mirrored on the other?

I have played with the settings in HDSDR a little and managed to make the spike almost disappear visually by adjusting the bandwidth of the auto correction, but this didn't get rid of the mirrored signals and also there was still some affect on the signal at center frequency.

What is the best practice for calibrating the SDRPlay for zero, or close to zero unwanted signals?
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Quimquim
Posts: 28
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Location: Quebec Canada

Re: IQ Correction

Postby Quimquim » Tue May 19, 2015 1:47 pm

Welcome aboard Bristolpirates

Did you take a look at the DaveB post --- Removing Zero IF Image signals in FM Broadcast Band --- it could help you with some questions you have about the IQ calibration.

Have fun with your new SDRPlay RSP....

Regards
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Stay tuned !!!! :mrgreen:

Quimquim :P


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