RTL-SDR Low Signal Strength on Record Signal

[cspain]

Windows 10 using NooElec RTL-SDR USB Dongle:

Signal when using the spectrum analyzer/tuner is good, but when recording the signal is very weak - sometimes barely above the noise despite the gain being turned up.

This problem was briefly mentioned in Issue #162.

Thank you.

[andynoack]

Confirmed under Gentoo with gain 50. We will search for the bug!

Edit: rtlsdr seems to need ludicrously high gain values (300-400). We will improve the GUI to get aware of the maximum gain levels

[jopohl]

@cspain what backend are you using? Native Backend for RTL-SDR works fine on Windows 10 for me.

Edit: How high did you turn your gain?

[cspain]

I have attached some screen grabs with the issue. Maybe the noise floor is too high. Thanks!

…

On Mar 1, 2017 4:13 AM, "Johannes Pohl" ***@***.***> wrote: @cspain <https://github.com/cspain> what backend are you using? Native Backend for RTL-SDR works fine on Windows 10 for me. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#177 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AB_AOxoqpsTRcVzMzGn7JNkDMZ_8o1Haks5rhTbAgaJpZM4MPK5H> .

[jopohl]

@cspain I can not see your screen grabs. Maybe try putting the gain to 300 like @andynoack mentioned?

[cspain]

Putting the gain to 300 worked. Thank you. This tool is great by the way and I appreciate all the work put into it and the fact you're sharing it.

…

On Mar 1, 2017 8:44 AM, "Johannes Pohl" ***@***.***> wrote: @cspain <https://github.com/cspain> I can not see your screen grabs. Maybe try putting the gain to 300 like @andynoack <https://github.com/andynoack> mentioned? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#177 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AB_AO5gcnOGLjileICtzouS1nvGHT9Upks5rhXZTgaJpZM4MPK5H> .

[jopohl]

You're welcome @cspain . Glad it works now!

[flacombe]

Hi

I've also had this problem last sunday during my tests

RTL-SDR devices' gain is limited to 40, how would you do to set it to 300 ?
Why spectrum analyser works well without this 300 gain ?
It seems pretty unrealistic to set gain to 300, it's a really high value

By the way, as cspain said, the works done here is huge and highly appreciated, big thank you !

[cspain]

I was limited to 40 gain in the past (maybe an earlier build) , when I tried it again today I was able to set 300.

…

On Mar 1, 2017 2:26 PM, "Gustave" ***@***.***> wrote: Hi I've also had this problem last sunday during my tests RTL-SDR devices' gain is limited to 40, how would you do to set it to 300 ? Why spectrum analyser works well without this 300 gain ? It seems pretty unrealistic to set gain to 300, it's a really high value By the way, as cspain said, the works done here is huge and highly appreciated, big thank you ! — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#177 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AB_AO8gvsA6cKfiiYqTnET0B95elr4Ptks5rhcZVgaJpZM4MPK5H> .

[jopohl]

HI @gustavecha ,

as @cspain correctly assumed it was indeed a buggy limitation in an earlier version to restrict RTL-SDR to gain 40. RTL-SDR API demands such high values, there is nothing much I can do about it.

The whole gain setting will be made clearer with implementation of: #148. I will add a slider for the gain, so it becomes obvious what the maximum gain for a device is.

[flacombe]

Understood this clear explanation :)

I assumed RTL-SDR gain was limited to 40 by refering to max value used in SDR# / RTL_TCP with this output in console : "Setting gain value to index 40".
Are we sure it's only on RTL SDR API ? Spectrum analyzer works well with low gain

[jopohl]

The "Setting gain value to 40" is message from URH. It has some maximum values for each device built in to prevent unneeded API calls and provide a maximum for the GUI elements.

You see only the frequency in spectrum analyzer: If you record with gain 40 you also see a signal, it is just quite weak. However, this is enough for FFT to perform its magic and show you the frequencies fo the signal.

[flacombe]

Regarding the 'Setting gain value to index 40', I was talking about what is shown in console when I use RTL_TCP with SDR#, it wasn't about URH.
Such a message make me thought the gain was actually limited to 40 in RTL SDR API.

Ok for spectrum analyzer, seemed legit as I read it, Thx :)

[jopohl]

Oh sorry I misread your first comment. Seems to be a quite funny coincidence here:

• 40 was the value hardcoded for max gain for RTL-SDR in previous version
• Setting gain value to index 40 indicates, that there are 40 gains available and RTL_TCP/SDR# are choosing the last one in the array i.e. the greatest.

[flacombe]

Sounds good :)
And then, I definitely don't know what the highest value is, maybe 300 and accessed at the index 40

Have a nice evening