Output power limesdr

#8

Hello Joel,

|Sorry for the delayed response. Glad to hear you managed to duplicate the results. I used a span of 10MHz for the test, where RBW and VBW ratio was 100. This should not affect your results nonetheless, since the signal level should still be far above the noise floor of your analyzer (and no close proximity signals should be present for the need to separate them). Reference level was 20dBm with 30dB attenuation (wrong settings for these could indeed affect your signal level).

RBB tab settings are not important in your case, since these actually control the analog filter for the receive chain (not transmit).

Tweaking bias settings can indeed help to push the output power value higher, but bear in mind, that you are only increasing DC value at this point - at normal operation you would be oversaturated and driving the chain in the non-linear range.

+10dBm is the realistic output power for a modulated signal (not CW) that can be sent without distorting the signal.

Regards,
Karolis

LimeSDR maximum Transmit power clarification
made this topic public #9
#10

Hi,

Can the TX_power_measurement.ini file be attached to this topic?
It seems gone from Dropbox. If it is attached at least all state is preserved in this forum.

Thanks
Job

#11

Hi Karolis,

I am new to LimeSDR. I am trying to do a similar measurement of the LimeSDR (output power against frequency).
I saw that you upload to this post the “TX_power_measurement.ini” file that you used to make this measurement. Unfortunately this file is no longer available. Can you upload it again?

You also wrote on this post several notes about how you configure some other register/parameter of the LimeSDR in order to reproduce your measurement.
I don’t see that you recommend to perform calibration on the TX path before doing the measurement. For this kind of measurements, calibration is not needed?

Thanks in advance
Mauro

#12

Hello Mauro,

welcome to the LimeSDR community. The removed file(s) will be uploaded to a more permanent location on a server till end of Friday so that it can be accessed for a longer time. I will notify you separately on this. Please note, that the provided state is meant only for maximum CW power measurement of LimeSDR board - it should not be used for communication setups. For that, use default settings and fine tune the RF chip to wanted levels of performance.

Calibration is not needed (and in fact not recommended) in this type of measurement, since TX chain is over-saturated. Under normal working conditions, you would want to use Calibrations (TX side - BB filter bandwidth tune->Gain tune-> DC and IQ imbalance cal.; RX side - BB filter bandwidth tune-> DC and IQ imbalance cal.).

Regards,
Karolis

#13

Hello Mauro,

as I wrote earlier, here is the link to the mentioned files:

http://downloads.myriadrf.org/project/limesuite/helpers/

Regards,
Karolis

#14

Hi Karolis,
Thanks for the information and the help!

Regard
Mauro

#15

@Karolis (or @andrewback ?) : could you explain what is set specifically by using your .ini file in order to get that much output power in LimeSuite? More importantly for me, are these power levels achievable in soapysdr or osmosdr?

With grc or pothos (so osmosdr or soapysdr), when I set the max gain value, I reach max output powers between -33 and -35dBm like @rodrigo7x mentioned (with a cable connection from the LimeSDR USB to an analyzer or another Lime)

#16

@Karolis, @andrewback, no idea on this? Can we achieve a 0dBm output with soapy or osmosdr?

#17

I would have thought so, unless Soapy is somehow restricting the gain range.

More generally would recommend using gr-limesdr blocks instead of gr-osmosdr, since these provides a more direct route via a lower level API, with additional features also.

#18

@andrewback : Max gain in soapy for the lime is set by this method https://github.com/myriadrf/LimeSuite/blob/master/src/API/lms7_device.cpp#L994. Soapy actually calls LMS7_Device::SetGain from here (https://github.com/pothosware/SoapySDR/blob/master/lib/Device.cpp#L276 and here https://github.com/myriadrf/LimeSuite/blob/master/SoapyLMS7/Settings.cpp ) with a value of 64 max for TX.

  • Are these values the max values for the Lime? Could it be that the call to LMS7_Device::SetGain for TX is wrong?

  • If I want to max output without distorting my signal, what should be max PAD and IAMP values? If you also have some link to documentation on the choices of these values, I’d appreciate.

Thanks for the help!

#19

This is one for @Zack or @IgnasJ.

#20

The maximum Tx gain value from soapy is 64. Using it should cause distortion because of saturation if you are utilizing close to full DAC range.

If you are talking about values in soapy, then PAD should be 52 (max), and IAMP should be 0 to guarantee that there is no saturation in IAMP stage at max DAC output. However, for a lot signals IAMP values 3-6 can be used without noticeable distortion if higher gain is needed.

#21

@IgnasJ: Thank you. With PAD=52 and IAM=0 (equivalent to soapy gain of 52), what could be the expected output power, for instance for a CW or whitenoise signal of bandwidth 10MHZ ? And with PAD=52 and IAM=3 or 6? Could you make the test for me?

Here, I get -36dBm when sending whitenoise on 10MHz bandwidth at 2.45GHz.

#22

@IgnasJ, @andrewback : any news? Could you test with GRC or Pothos what max value you get with a simple CW or Whitenoise signal?
I tested with a friend on his own LimeUSB directly plugged to his RF wattmetter, and we also got results far from 10dBm (around -26dBm)

#23

To have an answer would be so much appreciated, @IgnasJ …

#24

@ChrisLM,

Look here ----> More About The Power Level of the LimeSDR 160m to 1.28 GHz

73 de Marty, KN0CK

#25

Thanks @martywittrock ! Would you have the same data but at 2.4GHz ?
I’m going to try SDRAngel to compare with GRC and Pothos.

#26

@ChrisLM,

Can’t help you there - my spectrum analyzer only goes to 1500 MHz and all the measurements I made with my LimeSDR USB are based on three tuned measurements at each frequency to get the actual value (peak, and not too many varied that much measurement to measurement). There is data that @Karolis has performed on the LimeSDR USB and LimeSDR Mini for those frequencies above 1.2 GHz and they do appear on this forum if you do a search on ‘transmit power’. It also appears here on Myriad:

…and also here if you look at the curve more toward the bottom of the page:

https://wiki.myriadrf.org/LimeSDR_HF_Performance

Hope this helps -

73 de Marty, KN0CK

#27

Hi,
I tested LimeSDR-USB output using SoapySDR API to send sine IQ samples .
Center frequency 2.45GHz; sine tone offset +1MHz; antenna BAND2; sample rate 10MHz; bandwidth 10 MHz.
I got the following levels reported by spectrum analyser.
Soapy gain=52 -> ~ -7.0dBm
Soapy gain=55 -> ~ -4.0dBm
Soapy gain=58 -> ~ -2.0dBm
Soapy gain=61 -> ~ -1.0dBm

distortion (additional harmonics) above gain setting 55 was clearly visible.