I am currently working on the simulation of FMCW radar using a pluto SDR for my major project, I am using rev B of the SDR, I have written the code for the generation and transmission of the baseband chirp. I tried transmitting it and checking the output with a spectrum analyzer, the result of this was that I was not able to see the whole spectrum of the transmitted frequencies in a single go but when I changed the analyzer setting from clear & Write to Max hold, I could see the spectrum as i want it. So, I needed some help in transmitting the spectrum all at once. Below is the python code used by me to generate and transmit the chirp, the video which shows the issue faced by me.
import time
import adi
import numpy as np
import time
# Create radio
sdr = adi.Pluto(uri="ip:192.168.2.1")
# Configure properties
sdr.sample_rate = 60000000 #60e6
sdr.tx_rf_bandwidth = 20000000 #20e6
sdr.tx_lo = 2400000000
sdr.tx_hardwaregain_chan0 = -20
sdr.gain_control_mode_chan0 = "slow_attack"
# Configuration data channels
sdr.tx_enabled_channels = [0]
# Create a waveform
sample_rate = sdr.sample_rate
center_freq = sdr.tx_lo
pulse_duration = 140e-6 # sec
num_samps = int(sample_rate * pulse_duration)
if(~(num_samps%1024)):
num_samps = 1024*(num_samps//1024)
if(num_samps == 0):
num_samps = 1024
print(num_samps)
bandwidth = sdr.tx_rf_bandwidth #20e6
# Create transmit waveform
# Create axis for transmitted chirp
time_axis = np.linspace(0, pulse_duration, num_samps)
f0 = - bandwidth / 2
f1 = + bandwidth / 2
c = 3e8 # Speed of light
alpha = bandwidth / pulse_duration
# Generation of transmitted signal
trans_chirp = np.exp(1j * 2 * np.pi * (f0 * time_axis + (alpha * time_axis ** 2) / 2))
trans_chirp = 2*14
t_end = time.time() + 60 * 5
while time.time() < t_end:
sdr.tx(trans_chirp)
when we check the fft of the transmitted signal we get a full spectrum of the transmitting frequencies like shown in the figure below but when we check the actual transmitted signal on spectrum analyser that is not the case. Sorry but I don't understand what part of my code is missing.
in the above video shouldn't I be getting the Spectrum that I get at max hold normally too.
