[USRP-users] Removing the whole LO signal when transmitting

Brais Ares bares at gradiant.org
Tue Jul 18 11:28:14 EDT 2017

Ok, then I could say my loopback looks good enough.

Thank you for all your help and provided information. I'll check the links
you've shared as soon as I can.


2017-07-17 12:28 GMT+02:00 Derek Kozel <derek.kozel at ettus.com>:

> Hello Brais,
> The gain values for USRPs are indexed from 0 dB gain being minimum gain up
> to the device's maximum. Usually this means that 0 dB of gain is actually a
> large amount of attenuation or loss through the RX chain. The same is true
> for TX. It doesn't surprise me that you are seeing those values.
> Ideally you will experiment to find an operating point on RX to maximize
> the signal quality (minimize Noise Figure and capture the maximum dynamic
> range) of your digitized signal. The performance data for the
> daughterboards can help with this. There are similar tradeoffs on the TX
> side.
> http://files.ettus.com/performance_data/
> Also be sure to run the self-calibration routines if your daughterboard
> supports them. This can improve the signal quality significantly. Marcus
> has also mentioned UHD's ability to do LO offsetting to move it outside of
> your passband, definitely worth investigating.
> Regards,
> Derek
> On Mon, Jul 17, 2017 at 11:47 AM, Brais Ares via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>> Ok, I understand!
>> Also I have to configure a rx_gain of 60 dB, and a tx_gain of 10 dB If I
>> want to reconstruct the transmitted signal to the very same power level I
>> received it.
>> The scheme would be:
>> ~~~ signal_generator (QPSK at -60 dBm) -> cable(0.3 dB attenuation) ->
>> rx_usrp -> tx_usrp -> cable(0.3 dB attenuation) -> Signal analyzer (I want
>> to obtain original power here, -60 dBm).
>> *Is it normal that I have to apply roughly 70 dB of gain to replicate the
>> incoming signal?*
>> @Karan, did this happen to you?
>> ​Appreciate all the help, guys
>> Regards,
>> Brais.​
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com


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Brais Ares Fernández
Investigador - Desarrollador | Área de Comunicaciones Avanzadas
Researcher - Developer | Advanced Communications Department

Ph. (+34) 986 120 430  Ext. 3019
bares at gradiant.org  |  www.gradiant.org

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