Using RX2_L below 30 MHz on GNU Radio

Hello everyone,

first of all: i’m pretty to the forum and i couldn’t find a solution in the other topics, so please tell me if i missed something or this is the wrong category! :slightly_smiling_face:

So what i am trying to do is measuring the reflectioncoefficient (so kind of an VNA) with the two inputs of the LimeSDR USB. I am using different frequencies for that but only CW as you might imagine.

To calculate my data i am using GNU Radio 3.7 with the gr-limesdr from Myriad.

I used the easy Fix 2 to fit RX1_L and RX2_L to my requirements and it actually works pretty well all over the whole frequency range (for CW), but only on Channel 1.

Channel 2 rapidly drops if i go under 30MHz and i don’t know why… i have the exact same settings for both of the inputs and applied the EasyFix2 for both matching networks.

here you see my FFT Plots for 30 MHz and 29.9MHz with the exact same application


Since i don’t even know where to start with this issue i thought maybe some of you at least have an idea why this happens.

P.S. same thing happens with RX2_W, so maybe it’s a software problem of gr-limesdr or GRC… please let me know if i should visit another forum then

Thanks and best regards