Hello,
please take a look at this post: Trouble using NCO to transmit at lower frequencies
I have the same problem. I’m trying to use LimeSDR Mini to transmit a sinusoidal signal in the range (21 MHz - 100 MHz) i.e. a simple carrier without any modulation / tone.
When I get to frequencies below 60 MHz, the signal gets really degraded.
Around 30 MHz I’m not able to calibrate Tx and Rx anymore.
I’m not sure if it’s a problem of the LimeSDR Mini Hardware or a problem in the API that could be avoided by programming the board in a “lower” level.
What is for sure is that the sinusoidal output signal has not the expected quality I’d like. As @yt7pwr said, it might be that the board transmit at the intended frequency and that you might be able to read this frequency with a spectrum analyzer, but the signal in this form has not the quality I’d need for my application. I’d like to know however if it’s the board Hardware or the API the source of the problem.