I received a weird error when using the limeSuiteNG plugin in GNU Radio in Linux for my Mini v2. Is there any relationship between the frequency sent out and the sample rate? When I set the sample rate for the source to 1k. It outputs an error: LimeSuiteNG :error: lms7002m_set_frequency_cgen: cannot deliver requested frequency (128000 Hz). When I set it to 10k, it outputs an error: LimeSuiteNG :error: lms7002m_set_frequency_cgen: cannot deliver requested frequency (1280000 Hz). However, I set a fixed 40M LO to both transmitter and receiver. Is the transmitted frequency also related to the sample rate of the receiver? Where does the magic frequency 128xxxx come from? Thanks in advance!
Hi, LO and sample rate frequencies are not related.
Your used LO is fine and within the hardware parameters. But the sample rate is not. The hardware has limitations, the sample rate of the sink and source has to be equal, and more than 100k.
It’s a result of your requested 10k sample rate and maximum available RF oversampling by 64, multiplied by the LMS7002M 2 channels 10k x 64 x 2. That’s the frequency that is required from the clock generator inside the LMS7002M chip to satisfy the requested sampling rate, but the clock generator has limited range and cannot satisfy such low sampling rate frequency.
Thanks, Ricardas! It really clarifies things for me. Now I get the GNU Radio working!
However, I get a signal from the receiver even though I haven’t put any antenna on. I try to send out a 5khz sin wave, but the received wave contains multiple of 5khz frequency. ±10khz, ± 15khz , etc…. [the picture below]. If I connected the antenna, the signal will be stronger as expected but there are still multiple of frequency.
I have two questions.
1: Where the leakage coming from without putting antennas? Is it coming from the single LO shared by the transmitter and receiver? I also tried the case where input a contant signal and use the NCO offset to generate the sin wave, the leakage become less but still exist.
2: Why there are multiple frequencies? The calibration may not be perfect, which may gives symmetric frequency ±5 khz and DC. However, I don’t quite understand why there are multiple of frequencies (±10, ± 15) shows up in the spectrum. Thanks for your fast response again! I really appreciate it!
Analog is not my expertise, so can’t really answer that. Considering that your Tx gain is pretty high there would definitely be some kind of leakage or crosstalk. The NCO within LMS7002 uses dithering, so that could explain the signal difference from generating sine yourself.
I don’t know, some kind of harmonics. Can’t really know what’s causing them without experimenting, try increasing your sampling rate and reducing oversampling, see if anything changes.
