# Why does a peak remain at -10db gain and disappear at -50db gain?

I have a Pluto and an RTL-SDR both connected to a computer. On Matlab, I run such a script:

%Script

SAMPLE_RATE = 750e3;
NUM_SAMPLES = 750e3;
CENTER_FREQ = 868e6;
TRANSMITTER_GAIN = -10;

deviceNameSDR = 'Pluto';
sdrTransmitter = sdrtx(deviceNameSDR);

sdrTransmitter.BasebandSampleRate = SAMPLE_RATE;