Communication link analysis

Link budget calculator

Change any parameter and every result updates. Start from a band preset, then enter your own hardware figures.

Received power

-113.14dBm

-143.14 dBW

C/N0

58.47dB-Hz

SNR 14.49 dB in 25.0 kHz

Eb/N0

18.65dB

Required 9.59 dB

Link margin

9.06dB

Link closes with a healthy margin

Preset and carrier

Band preset

1 W at 437 MHz into a 14 dBi crossed Yagi, 9.6 kbit/s BPSK. Representative values for teaching.

Frequency

MHz

Transmit power

0.00 dBW, 30.00 dBm

Geometry

Where the satellite is relative to the station

Satellite altitude

Elevation angle

Slant range used: 1,695.1 km

Antennas and losses

Transmit antenna

Gain

dBi

Receive antenna

Gain

dBi

Transmit feeder loss

Receive feeder loss

Atmospheric absorption

Rain fade

Polarization mismatch

Pointing loss

Other losses

Receiver and requirement

Noise

System noise temperature

Noise bandwidth

kHz

Data rate

kbit/s

9.60 kbit/s

Modulation

Target bit error rate

Enter the required Eb/N0 by hand (coding gain, implementation loss)

BPSK needs 9.59 dB for BER 1e-5 without coding.

Budget

Each line adds to or subtracts from the carrier

Link budget lines
Transmit power	0.00dBW
Transmit antenna gain	0.00dBi
Transmit feeder loss	-1.00dB
EIRP	-1.00dBW
Free-space path loss	-149.84dB
Atmospheric, rain, polarization, pointing, other	-4.30dB
Receive antenna gain	14.00dBi
Receive feeder loss	-2.00dB
Received power	-143.14dBW
Noise density N0 = kT	-201.61dBW/Hz
Noise power N = kTB	-157.63dBW
G/T	-14.99dB/K
C/N0	58.47dB-Hz
SNR	14.49dB
Eb/N0	18.65dB
Required Eb/N0	9.59dB
Margin	9.06dB

Margin versus elevation

Satellite at 500 km, every other input fixed

Equations used

Wavelength: $\lambda = \dfrac{c}{f}$
Free-space path loss (ITU-R P.525): $L_{fs} = 20\log_{10}\!\left(\dfrac{4\pi d}{\lambda}\right)\ \text{dB}$
Parabolic antenna gain: $G = \eta\left(\dfrac{\pi D}{\lambda}\right)^{2}$
Received power: $P_r = P_t + G_t - L_t - L_{fs} - L_a + G_r - L_r$
Noise power: $N = kTB,\quad 10\log_{10}k = -228.6\ \text{dBW/K/Hz}$
Signal to noise: $\dfrac{C}{N_0} = P_r - 10\log_{10}(kT),\qquad \dfrac{E_b}{N_0} = \dfrac{C}{N_0} - 10\log_{10} R_b$
Link margin: $M = \left(\dfrac{E_b}{N_0}\right) - \left(\dfrac{E_b}{N_0}\right)_{req}$
Slant range from elevation: $d = \sqrt{(R_e + h)^2 - R_e^2\cos^2\varepsilon} - R_e\sin\varepsilon$