TX Phase and Gain control

Good evening,

I was testing the LimeSDR transmitter by transmitting a train of sinc pulses. However, I noticed that they follow a particular pattern along the train, varying their gain and phase, as you can see from the image screens below.

The first image is a close up of the pulses I’m transmitting:

The second image is a zoom out of the pulse train and you can see some sort of “modulation” that prevents the pulses from having a constant gain and phase, like I intended:

I’ve read the datasheet and the programming guide, and tested a few options but without sucess. Where exactly should I look to solve this problem? How can I transmit all the pulses with the same gain and phase?


@Zack @andrewback, can you help me? I still wasn’t able to solve this. Furthermore, how can I correctly control the exact time I transmit a single pulse? I think I’m using timestamps wrong because in the oscilloscope I see the pulse at slighty different times (I mark the beginning of transmittion with a gpio set to high).

How are you generating the signals to the scope? Is the carrier de-modulated somehow?

If not, with a sample rate of 1Ms/s, you’re probably undersampling badly, and the modulation you are seeing is just an undersampling artifact.

Hi @OCB,

As Carl mentioned, how are you measuring Tx RF output? Is 1MS/s sampling rate of the scope enough?