USRP 2920 carrier no modulation

[JLannoo]

Hi everyone,

I started programming in LabVIEW for the USRP 2920. I messes around with the receiving part and everything works just fine.

Next, I wanted to try some basic modulation methods, but before going in to difficult stuff, I just tried to get a carrier out of the USRP.

In attachment I show you the program in LabVIEW where I just send an array with "ones" to the USRP, the carrier is configured to be 50MHz.

By first observing on a spectrum analyser, the signal looked ok, but the magnitude was smaller than expected (not 0dBm for example). Then, by zooming out, it appears that there were some harmonics too, which explained where the rest of the energy went. I viewed the same signal on a high-speed scope (see attachment). I expected a pure sinusoid, as that is what a carrier should be, but no, I see a strange periodic signal.

Can anyone help me why I have this signal as the output? If you need more info, let me know.

Best regards,

JLannoo

[IDASYAN]

Hello, 

Could You please describe whole Your system, how is it connected to the host. And try to run simple USRP example. The loss You are having is undetected, it might be something else.

Regards.      

[JLannoo]

Hi IDASYAN,

Thanks for your response! My answer comes a bit late because I could not be in the lab to continue measurements with the USRP equipment.

The whole setup: laptop running Labview 2020 --> USB type C to Ethernet dongle to NI USRP-2920 --> SMA cable to Keysight MSOS404A scope (4GHz 20GSa/s 10bit ADC) input impedance : 50 Ohm.

The example program I ran is "niUSRP Tx Continuous Async.vi" with settings:

IQ Rate: 1MHz

Carrier Frequency: 50MHz

Active antenna: TX1

Gain: 0 dBm

Timeout: 10

Tone frequency: 0Hz

Tone Amplitude: 1

Waveform size: 10000

If I change the carrier frequency to higher, the harmonics raise accordingly.

I have a separate spectrum analyser (R&S FSC6 Spectrum Analyser) which shows the same signal when I connect the SDR to it with the same program running.

In attachment I have the following files:

- Printscreen of Labview example program

- Picture of the setup in the lab

- Printscreen of the scope

- Printscreen of the spectrum analyser

If you need any more information to help me, let me know.

Best regards,

Jonas