Using the rtl2832 in direct sampling mode with hardware modification

[Brian Butler]

 Hi, has anyone got the direct sampling operation on the RTL2832 working? I have seen a post recommending that the device string "direct_samp=1" can be entered on the I/O config window. My experience is that the device is automatically switched to "Other" rather than the RTL2832 device, thus indicating that the RTL2832 will not accept direct_samp=1. The reason I ask this is in order to get the RTL820T2 dongle operating with the modification  where a transformer has been fitted to apply an input directly to the Q input pins of the RTL2832 device. I also query if the actual string should be device_samp=2 as I have seen somewhere that 2 refers to the Q inputs.

Brian G4LUL
 

[Alexandru Csete]

On Wed, Jul 22, 2015 at 8:00 AM, Brian Butler <brian...@gmail.com> wrote:
>
> Hi, has anyone got the direct sampling operation on the RTL2832 working? I
> have seen a post recommending that the device string "direct_samp=1" can be
> entered on the I/O config window. My experience is that the device is
> automatically switched to "Other" rather than the RTL2832 device,

I think that the "Other" is just a feature of the
gqrx/gr-osmosdr/rtl-sdr combination and happens regardless of direct
sampling or not. The device strig should still be correct.

> indicating that the RTL2832 will not accept direct_samp=1. The reason I ask
> this is in order to get the RTL820T2 dongle operating with the modification
> where a transformer has been fitted to apply an input directly to the Q
> input pins of the RTL2832 device. I also query if the actual string should
> be device_samp=2 as I have seen somewhere that 2 refers to the Q inputs.

Here is the official documentation of the device string parameters:
http://sdr.osmocom.org/trac/wiki/GrOsmoSDR#RTL-SDRSource
It suggests that you are correct.

Alex

[Charles Albert]

I too am trying to get my Blue Direct Sampling RTL (BA5SBA) to work on HF.

I tried the direct_samp=1/2 and neither gave me any output when set to a local AM BC station at 600 KHz.

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[Brian Butler]

On Wednesday, July 22, 2015 at 7:00:54 AM UTC+1, Brian Butler wrote:

 Hi, has anyone got the direct sampling operation on the RTL2832 working? I have seen a post recommending that the device string "direct_samp=1" can be entered on the I/O config window. My experience is that the device is automatically switched to "Other" rather than the RTL2832 device, thus indicating that the RTL2832 will not accept direct_samp=1. The reason I ask this is in order to get the RTL820T2 dongle operating with the modification  where a transformer has been fitted to apply an input directly to the Q input pins of the RTL2832 device. I also query if the actual string should be device_samp=2 as I have seen somewhere that 2 refers to the Q inputs.

Brian G4LUL

Hi Alexandru,  Well I have now tried rolling back to the previous version of Ubuntu as I saw a comment that the RTL device had problems with the latest v15 of Ubuntu, now get a complete failure due to Gnu radio #bug528 and from what I see nobody seems able to cure it. So don't know where  to go from here, what version of Linux do you run this GQRX on and can you confirm that the direct sasmpling mode works on your Linux machine.

Regards Brian

 

[Alexandru Csete]

On Wed, Jul 22, 2015 at 5:58 PM, Brian Butler <brian...@gmail.com> wrote:
>
> Hi Alexandru, Well I have now tried rolling back to the previous version of
> Ubuntu as I saw a comment that the RTL device had problems with the latest
> v15 of Ubuntu, now get a complete failure due to Gnu radio #bug528 and from
> what I see nobody seems able to cure it. So don't know where to go from
> here, what version of Linux do you run this GQRX on and can you confirm that
> the direct sasmpling mode works on your Linux machine.

I am not using this configuration so I can not tell about performance
and such, but I can run gqrx with an rtl dongle using
"rtl=0,direct_samp=2" device string and it appears to work (I see
noise floor).

I can't help based on the information you provide. Please be specific
about which version of Ubuntu you installed and in particular how you
installed gqrx. We recommend using the snapshots PPA:
https://launchpad.net/~gqrx/+archive/ubuntu/snapshots/+packages
But be careful not to install from mixed sources.

If you get an error try copy & pasting the complete error message into
an email. It could be something as trivial as needing to blacklist the
DVB driver and the error message often includes clues.

Alex

[Brian Butler]

Hi Alexandru
The version of Linux is 14.04.2 and this is the one that gave me the 528bug message. The version that appeared to work was vers 15.04, I too got a noise floor after entering the new string data but it was soon apparent that it was not working, I assume you are supposed to manually adjust the local osc freq to obtain the correct frequnency reading for Direct Sampling mode. Anyway I will go back to the vers 15 and have another try, at least it did something .As for the installation of GQRX I picked it up off the official GQRX site gqrx.dk  where there is a link to the site that you mention. Will press on regardless....
 Brian

[Brian Butler]

Hi Alexandru

Thanks for the reply, I have now managed to get the RTL Dongle working in direct mode, using the direct_samp=2, which as you agree is the correct setting for the Q inputs on the RTL2832. I did look at the site you directed me to ( https://launchpad.net/~gqrx/+archive/ubuntu/snapshots/+packages ) but have to admit that I am completely lost as to which files to download and how to go about it. Sadly the the site does not have any guidance that I could find.

 Another PC was also set up with Ubuntu 15.04 and that worked fine with the source of software undefined and it is version 2.3.1-2 build 1. This software was downloaded using the  Ubuntu 15.04 Software Centre.   I did  set the software sources in my Ubuntu 15.04 Software Centre to use the ppa: details for the site you reccomended as one of its preferences, unfortunately what ever files it downloaded did not work despite saying that it was vers 2.3.1-2 build1. I must assume that despite the versions being the same there are some sublte differences between them.

The ppa site was removed from the Software Centre listing and whatever it downloaded next worked OK.

Regards Brian

On Wednesday, July 22, 2015 at 8:42:44 PM UTC+1, Alexandru Csete wrote:

[jmly...@gmail.com]

I tried rtl=0,direct_samp=1 today and got a crash dump.

Is a hardware modification required for this to work?

Thanks, James
Ubuntu 14.04LTS, HP 15 AMD64 Quadcore