Max real output power vs theoretical value?

#1

Hi,

Would anyone have measured the max output power of his LimeSDR-USB ? Could anybody make the small test below and tell me the value they get?

I get repeatedly with Soapy or Osmosdr values of -33 to -26dBm far below the +10dBm announced by LimeMicro team. With Soapy (Pothos actually) or osmosdr (GRC), when sending with a gain of 52 some white noise on 1 or 5MHz wide (CW) or a pure sinusoidal, with the lime usb directly attached by a SMA cable to a RF powermeter (a pro tool from R&S), I get the dBm written above. I can of course increase gain to 64, but distortion arises as expected (and output goes up to -20 -18dBm).

Lime team published once a .ini file for Limesuite to, say, reach 10dBm, but Limesuite is so little documented that the .ini is almost unusable to understand the difference between Soapy or Osmosdr and Limesuite…

Thanks for your help!

#2

@ChrisLM,

How long is the attached SMA cable? Has it been characterized to remove its loss from the measurement? Are you running any attenuation on the input of the power measurement system (R&S Pro Tool)? All these things need to be understood before anyone can take any next steps. As I mentioned in a prior post on the same subject, if you look at the power levels at 2.0 GHz for the TX_1 and TX_2 RF outputs of the LimeSDR USB you will find the output level to be about -10dBm. If you have measurement losses in the cable that you have attached to the LimeSDR to the measurement system and have any attenuation at the input of the measurement system for protection, then it may explain some of the additional loss you’re seeing. Again, normalizing the setup using a calibrated RF generator at the frequency of interest and then getting that to align at 0dBm and then measuring the LimeSDR at the same frequency of interest will provide a more accurate RF measurement to understand the issue.

Finally, please - do not ‘spam’ the forum with the same (or similar) question asked in different threads - that’s a good way to get tossed off the forum. If you have messages of the same type asking the same info but on different threads, then get rid of one of the messages - okay?

73 de Marty, KN0CK

#3

My apologize for the delayed response @martywittrock, I was out for business, and thank you a lot for this deep answer.
It was actually the PA I put at the output that was faulty. My results are nearly the same as yours and as what my RF wattmeter says, so all is fine. Thanks again.

1 Like