MATLAB shows B200 USRP as transmitting but device is not physically transmitting.

I am attempting to transmit on a B200 USRP using matlab. The below code is what I am using to attempt to transmit a 100KHz sine wave at 433MHz center frequency. I have a seperate SDR monitoring 433MHz nearby (using independent software). I have verified the USRP platform, serial number, and have the more recent UHD driver installed on the USRP. I am running the latest version of MATLAB 2024b. Matlab finds the sdr when executing "findsdru" and "probesdru". When attempting to transmit I receive a "0" indicating no underruns. Everything performs in matlab as if nothing is wrong, however, the red transmit light doesn't illuminate on the USRP and I dont see the 100KHz signal on my independent device. These two indicators lead me to believe that the USRP isn't transmitting. I saw the red light illuminate when setting up the USRP with matlab so I know it works. I have used Matlab with other SDR's and I have the USRP communications toolbox downloaded too. Any help is much appreciated?

Code:

sinewave = dsp.SineWave(1,100e3); %generates a 100Khz sine wave
sinewave.SampleRate = 2e6; 
sinewave.SamplesPerFrame = 5e3; 
sinewave.OutputDataType = 'double'; 
sinewave.ComplexOutput = true;
data = sinewave();
tx = comm.SDRuTransmitter(...
    Platform = "B200", ...
    SerialNum = "F5EA7B", ...
    Gain=70, ...
    CenterFrequency = 433e6, ...
    InterpolationFactor = 128, ...
    TransportDataType="int16");


tx(data) 
%release(tx)

Answer 1

[Satyam]

Hi @Samuel,

It seems like your MATLAB code is executing without errors, but the USRP B200 is not actually transmitting. Here are some checks you can try to resolve this:

Gain and Interpolation Factor

• Ensure the Gain is within the valid range for B200 (typically 0–76 dB).
• Check that InterpolationFactor is supported for your sample rate.

Continuous Transmission

• Your code sends only one frame. The LED may not light for such a short burst. Use a loop for continuous transmission.

Antenna and RF Chain

• Ensure the correct antenna is connected to the TX port and the frequency (433 MHz) is supported by your daughterboard.

I hope it would resolve your query.