How to Improve level of transmitted signal?

Yesterday i successfully run dualrxtx example code in limesdr . I changed frequency from 1 ghz to 2ghz as shown in attached snap. And then i compile and run on LimeSDR using visual studio 2013. And transmit on TX1_2 . it transmitted successfully , checked on spectrum analyzer . but the level was very low ( -37 dbm ) . how to improve or can we improve level of the transmitted single tone ? image

From what I can tell the LimeSDR ( and HackRF and bladeRF) sensibly chose that their maximum output power is under the legal limit. And hence are “Exempted devices” under FCC 15.103 subsection C in CFR 47 (Code of Federal Regulations).
“( c ) A digital device used exclusively as industrial, commercial, or medical test equipment.”

A tiny bit of knowledge is all that is required to increase the signal levels beyond the legal limits.
1 external gain (LNA/Broadband RF amplifier/MMIC)
2 .an external band pass filter to put a hard limit on all intended (and unintended) transmissions to keep them all inside the legally licensed band.
By making you provide external equipment, it puts ALL of the onus on the person doing so to responsibly find out and obey all local legal requirements. If you don’t know how to to do something with RF, then you probably should not do it, not until you get an Amateur Radio operators license, and as part of the training you will find out all, the local legal requirements within your country.

Because they are classified as test equipment with unintentional (and in this case intentional) emission of radiation under ~10dBm, they avoid costly certification (which they would not pass because they do not block with a locked down firmware TX on bands licensed for very large yearly commercial fees by governments - which would be different for each country), and avoiding those certification fees, reduces the price point for consumers. Limiting the output under the legal limit also means that you do not have the case where some idiot buys a device with TX capability and decide to break laws and do stupid things on licensed bands at high power either unintended ( no knowledge ) or intentionally ( probably flagged as terrorist ).

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Thank you for your elaborated reply . it really helpful . I understand all the concerns you mentioned, i have also background in RF domain. with broadband power amplifier etc. my question was that is there any things to play with TRF TBB SXT etc etc for improvement of transmitted level without use of any external power amplifier etc .thanks

I’d be looking here TXTSP (15dB) and TXPAD (55dB) [ TRF ] combined could provide up to 70dB of gain.


Assuming you have not already modified these settings in dualRXTX.cpp:

  1. You can increase gain by changing: ‘LMS_SetNormalizedGain(device, LMS_CH_TX, 0, 0.4)’. Change 0.4 to 0.9 or 1.0.
  2. Signal on TX2_1 port should be higher than on TX1_1. You can make them same by choosing same RX test signal (they are loopbacked to TX in dualRXTX.cpp example) for both channels with LMS_SetTestSignal(), (LMS_TESTSIG_NCODIV8F has higher amplitude)
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using TX1_1 port . by changing ‘LMS_SetNormalizedGain(device, LMS_CH_TX, 0, 0.4)’. Change 0.4 to 0.9 or 1.0… level will considerably improve