# Determining the source data
Rз = 6371.0 # Radius of the Earth, km
RЭ = 8500.0 # Equivalent radius of the Earth, km
f = 49.0 # Frequency, MHz
P = 100.0 # Power, W
Δfc = 0.025 # Frequency band width, MHz
φN = 0.965167 # Latitude N, rad
λN = 1.448623 # Longitude N, rad
ΔhN0 = 0.162 # Altitude above sea level N, km
hN = 0.016 # Height of the antenna of the transmitter, km
Gφ = -2.0 # Gain of the transmitter antenna, dB
ha = 42000.0 # Apogee height, km
hp = 32000.0 # Perigee height, km
i = 0.17453 # The inclination of the orbit, rad
φM = 0.0 # Latitude M, rad
λM = 1.666789 # Longitude M, rad
ΔhM = 0.0 # Altitude above sea level M, km
N0 = -201.0 # Spectral noise power density of the receiver, dB
Gp1 = 22.0 # Antenna gain at frequency f1
Gp2 = 35.0 # Antenna gain at frequency f2
pfa = 1e-5 # The probability of a false alarm
ν = 1 # Number of frequency parameters
println("Initialization is completed")

θ0 = 0.981489 # Geocentric angle, rad
D = Rз * θ0 # Distance between PRD and PRM on the Earth's surface, km
println("Distance between PRD and PRM: $D km")

hM = 36423.578 # Height M above Ground, km
hM0 = ΔhM + hM # Altitude above sea level
println("Detector height above sea level: $hM0 km")

hN0 = ΔhN0 + hN # The height of the antenna of the transmitter above sea level
println("Height of the transmitter antenna above sea level: $hN0 km")

DM0 = 9187.426 # The range of direct radio visibility for the detector, km
DN0 = 55.009 # Range of direct radio visibility for PRD, km
D0 = DM0 + DN0 # Total range of direct radio visibility, km
println("Total range of direct radio visibility: $D0 km")

Dн = 39609.292 # Inclined range, km
Z0 = -32.45 - 20 * log10(Dн * f) # Attenuation in free space, dB
println("Attenuation of radio waves in free space: $Z0 dB")

Va = -0.02 # Attenuation in the atmosphere, dB
Vг = 0.0 # Attenuation in hydrometeorological formations, dB
V2 = Va + Vг # Total attenuation
println("Total attenuation in the atmosphere and hydrometeorological formations: $V2 dB")

Z = Z0 + V2 # Complete signal attenuation
println("Total signal attenuation: $Z dB")

# 1.24.2 Atmospheric noise level
Nш = -177.2 - 20 * log10(f) + 47.2 * (2.34 + 0.78 * log10(f))^(-2/3) + Gp1 # Atmospheric noise, dB
println("Atmospheric noise level: $Nsh dB")

PВт = 100.0 # The power of the transmitter in watts
Gp = 22.0 # Antenna gain on the main lobe
Z = Z0 + V2 # Complete signal attenuation
# Calculation of the signal-to-noise ratio
SNR = 10 * log10(PВт) + Gp - Z - N0 # Signal-to-noise ratio, dB
println("Signal-to-noise ratio at the receiver output: $SNR dB")

Qф = sqrt(2 * log(1 / pfa)) # The probability of a false alarm pfa
println("Normalized threshold level: $Qf")

X = SNR - Qф # Functional parameter
println("Function parameter X: $X")

if X < 0
    Y = (0.707 * abs(X))^2
    Pн = exp(-Y) # Probability of registration
    println("The probability of registering a radio signal by counting: $Ph")
else
    # If X >= 0, another formula must be used (you can add it if necessary)
    println("The functional parameter X >= 0, requires a different approximation")
end

# If we perform the calculation for the frequency f = 50 MHz
f2 = 50.0 # New frequency
Nш2 = -177.2 - 20 * log10(f2) + 47.2 * (2.34 + 0.78 * log10(f2))^(-2/3) + Gp1 # Noise level at 50 MHz
SNR2 = 10 * log10(PВт) + Gp - Z - N0 # Updated signal-to-noise ratio for f = 50 MHz
X2 = SNR2 - Qf

if X2 >= 0
    println("At a frequency of 50 MHz, the probability of registration = 1.0")
else
    Y2 = (0.707 * abs(X2))^2
    Ph2 = exp(-Y2)
    println("At a frequency of 50 MHz, the probability of registering a radio signal is: $Ph2")
end