Default Modulation

Projects LimeSDR
1

Hi, kind of a newbie question but I haven’t been able to find this information in the documentation or in the forum.

What is the default modulation that the Lime performs?

For example, in the C++ API, when I set my LO, set my sampling rate, setup a stream, and use the LMS_SendStream() function. Using a buffer with values in it, what can I expect the output to be?

Looking at it in an oscilloscope, it doesn’t seem to be amplitude modulation.

Could anyone share some insight into this?

Thanks

2

There is no “default modulation”. LimeSDR TX output is after D/A converter which is fed with I/Q data stream. Output can generate simple wave form as CW carrier or complex like DVB, 3G, QAM…

3

Thank you for your response

My question then is what is the role of the TX LO which is mixed with the data through the TXMIX module? What effect does it have on the output? Does mixing with an LO (Carrier wave) not constitute some kind of modulation?

4

TX LO is your transmit frequency +/- Fs/2 (maximum limits). For example: 144.5MHz is TX LO, sample rate is 1MS/s, your minimum TX frequency is 144 and maximum 145MHz. This is Ham radio band, allowed modulation schemes are CW, USB or FM (narow band).

5

I guess part of my misunderstanding is about the specific functionality of the TXMIX module. Given the analog I and Q signals, as well as a TX LO signal, how does the TXMIX module “mix” these signals together?