Adjacent Signal Interference
The following code can be used to calculate EMI between the antennas with adjacent frequency separations:
Pt = ; % Transmit Power (dBm/Channel)
NC = 56; % Noise Constant
Df = 20*log10(abs(dTRfr)); % dTRfr is the difference between the transmit and receive frequency (kHz)
NpC = Pt - NC - Df; % Noise per Channel (dBm/Channel)
Gt = ; % Gain of the transmit antenna in the direction of the receive antenna (dB)
ERNP = NpC + Gt; % Effective Radiated Noise Power (dBm/Channel)
PC = 32; % Propagation Constant
d = 20*log10(dTR); % dTR is the distance between the transmit and receive antennas (km)
freq = 20*log10(fr); % fr is frequency of the receive antenna (MHz)
L = PC + d + freq; % Propagation Loss (dB)
Gr = ; % Gain of the receive antenna in the direction of the transmit antenna (dB)
P_A = ERNP - L + Gr; % Available noise power at the receiver (dBm)
RxS = ; % Sensitivity of the receive antenna (dBm)
ADRxS = ; % Allowable degradation of the sensitivity of the receive antenna (if any, otherwise it is 0) (dB)
P_R = RxS + ADRxS; % Receiver Susceptibility Level or the power required to cause interference (dBm)
IM = P_A - P_R; % IM is the Interference Margin (dB)
if (IM < -10) % The if statement outputs the severity of the interference
disp('EMI is highly improbable');
elseif (IM >= -10) & (IM <= 10)
disp('EMI is marginal');
else
disp('EMI is probable');
end
Out of Band Interference
The following code would compute out of band interference.
Transmitter Harmonics Interfering with a Receiver's Fundamental Receptions (ft < fr)}
fr = ; % Receiver frequency (MHz)
ft = ; % Transmitter frequency (MHz)
N = round(fr/ft); % N is an integer associated with harmonics. It is rounded off to its nearest integer value
T_hf = N * ft; % Transmitter Harmonic Frequency (MHz)
fs = abs(T_hf - fr); % Frequency separation (MHz)
B_R = ; % Receiver bandwidth (MHz)
if fs >= B_R
disp('No harmonic interference occurs')
break
else
disp('Proceed');
end
The above code should firstly be run. If harmonic interference problem is
likely, the code would output "Proceed". The value of the Harmonic
Correction (H_C) should then be set based on the corresponding value of N.
Pt = ; % Transmitter power (dBm)
H_C = ; % Harmonic Correction (dB) that corresponds to the value of N
Hp = Pt + H_C; % Harmonic Power (dBm)
PC = 32; % Propagation Constant
d = 20*log10(dTR); % dTR is distance between the transmit and receive antenna (km);
e = 20*log10(fr); % fr is frequency of the receive antenna (MHz)
L = PC + d + e; % Propagation Loss (dB)
Gr = ; % Receive antenna gain in the direction of the transmit antenna (dB)
P_A = Hp - L + Gr; % Power available at the receiver (dBm)
P_R = ; % Receiver susceptibility level (dBm)
IM = P_A - P_R % Interference Margin (dB)
if (IM < -10)
disp('EMI is highly improbable');
elseif (IM >= -10) & (IM <= 10)
disp('EMI is marginal');
else
disp('EMI is probable');
end
Transmitter Fundamental Emissions Interfering with a Receiver's Spurious Responses (ft > fr)
fr = ; % Receiver frequency (MHz)
B_R = ; % Receiver bandwidth (MHz)
ft = ; % Transmitter frequency (MHz)
p = round(ft/fr); % p is harmonic of the Local Oscillator (LO), rounded off to the nearest integer value
fLO = ; % Frequency of the Local Oscillator (MHz), in the receiver
fIF = ; % Intermediate frequency (MHz)
fSR1 = abs(p * fLO + fIF - ft); % f1 at which receiver spurious response occurs
fSR2 = abs(p * fLO - fIF - ft); % f2 at which receiver spurious response occurs
m = max(fSR1,fSR2); % Maximum value of the two
if (m >= B_R)
disp('No Spurious Interference')
break
else
disp('Proceed')
end
The above code should firstly be run. If spurious response is
likely, the code would output "Proceed". The value of the Spurious
Correction (SC) should then be set based on the value of p.
Pt = ; % Transmitter power (dBm)
Gt = ; % Transmit antenna gain in the direction of the receive antenna (dB)
PC = 32; % Propagation Constant
d = 20*log10(dTR); % dTR is the distance between the transmit and receive antenna (km)
e = 20*log10(ft); % ft is frequency of the transmit antenna (MHz)
L = PC + d + e4; % Propagation Loss (dB)
P_A = Pt + Gt - L; % Power available at the receiver (dBm)
P_R = ; % Receiver fundamental susceptibility (dBm). This is equal to receiver sensitivity + allowable degradation
SC = ; % Spurious Correction (dB), value from Table 2 of the associated report which corresponds to the integer value of LO harmonic (p)
SS = P_R + SC; % Spurious Susceptibility (dBm)
IM = P_A - SS % Interference Margin (dB)
if (IM < -10)
disp('EMI is highly improbable')
elseif (IM >= -10) & (IM <= 10)
disp('EMI is marginal');
else
disp('EMI is probable');
end
Intermodulation
The following codes allow the calculations of both transmitter and receiver intermodulations.
Third Order Transmitter Intermodulation
This code determines the impact of the intermodulation product that may occur when signals from two transmit antennas mix in one of the transmitters, and then the combined signal is emitted to cause intermodulation in a receive antenna.
fr = ; % Operating frequency of the receive antenna (MHz)
ft1 = ; % Transmit antenna with frequency nearest to fr (MHz)
FS = abs(ft1-fr); % Frequency separation between the transmit and receive antennas (MHz)
FI = ft1 + FS % Frequency for intermodulation
ChW = ; % Channel Width (MHz)
IB1 = FI - ChW % Intermodulation Lower Band
IB2 = FI + ChW % Intermodulation Upper Band
ft2 = ; % Operating frequency of the second transmit antenna. If ft2 is within the intermodulation band then IMD is likely to occur otherwise not.
if (ft2 >= IB2) & (ft2 <= IB1)
disp('Continue with transmitter and receiver IMD Analysis')
else
disp('IMD does NOT occur in this particular case')
end
Pt2 = ; % Transmit Power of transmit antenna 2 (dBm)
Gt2 = ; % Gain of transmit antenna 2 (dB)
ERPt2 = Pt2 + Gt2; % Effective Radiated Power of transmit antenna 2 (dBm)
PC = 32; % Propagation Constant
d = 20*log10(dt1t2); % dt1t2 is the distance between the two transmit antennas (km)
e = 20*log10(ft2); % ft2 is the operating frequency of transmit antenna 2 (MHz)
L = PC + d + e; % L is the propagation loss
Gt1 = ; % Gain of transmit antenna 1
t2t1 = ERPt2 - L + Gt1; % t2 signal at t1
IC = 10; % Transmitter intermodulation Constant
PFS = 0; % Frequency separation. Either 0 or abs((ft1 - fr)/fr)*100 or 30log10(abs(ft1 - fr)/fr)*100 should be used, depending on whichever one is larger - the largest value should be used
Pint1 = t2t1 - IC + PFS; % Intermodulation power at t1 (dBm)
intERP = Pint1 + Gt1; % Intermodulation Effective Radiated Power (dBm)
d1 = 20*log10(dT1R); % dT1R is the distance between the transmit antenna 1 and the receive antenna (km)
e = 20*log10(fr); % fr is frequency of the receive antenna (MHz)
intL = PC + d1 + e; % Intermodulation Propagation Loss (dB)
Gr = ; % Receive antenna gain (dB)
PAint = intERP - intL + Gr; % Intermodulation power available at the receiver (dBm)
RxS = ; % Receiver sensitivity (dBm)
ADRxS = ; % Allowable degradation of the sensitivity of the receive antenna (if any, otherwise it is 0) (dB)
P_R = RxS + ADRxS; % Receiver susceptibility (dBm)
IM = PAint - P_R; % Interference margin (dB)
if (IM < -10)
disp('EMI is highly improbable')
elseif (IM >= -10) & (IM <= 10)
disp('EMI is marginal')
else
disp('EMI is probable')
end
Third Order Receiver Intermodulation
Receiver Intermodulation happens when signals from two or more transmit antennas mix within the RF amplifier or first mixer of the receive antenna. The following code computes the possible receiver intermodulation product, when two transmit antennas, having similar operating frequencies to that of the receive antenna, transmit.
fr = ; % Operating frequency of the receive antenna (MHz)
ft1 = ; % Transmit antenna with frequency nearest to fr (MHz)
FS = abs(ft1-fr); % Frequency separation between the transmit and receive antennas (MHz)
FI = ft1 + FS % Frequency for intermodulation
ChW = ; % Channel Width (MHz)
IB1 = FI - ChW % Intermodulation Lower Band
IB2 = FI + ChW % Intermodulation Upper Band
ft2 = ; % Operating frequency of the second transmit antenna. If ft2 is within the intermodulation band then IMD is likely to occur otherwise not.
if (ft2 >= IB2) & (ft2 <= IB1)
disp('Continue with transmitter and receiver IMD Analysis')
else
disp('IMD does NOT occur in this particular case')
end
Pt1 = ; % Power of transmit antenna 1 (dBm)
Pt2 = ; % Power of transmit antenna 2 (dBm)
Gt1 = ; % Gain of transmit antenna 1 (dB)
Gt2 = ; % Gain of transmit antenna 2 (dB)
ERPt1 = Pt1 + Gt1 ; % Effective Radiate Power of transmit antenna 1 (dBm)
ERPt2 = Pt2 + Gt2 ; % Effective Radiate Power of transmit antenna 2 (dBm)
PC = 32; % Propagation Constant
d1 = 20*log10(dt1r); % dt1r is the distance between the transmit antenna 1 and the receive antenna (km)
d2 = 20*log10(dt2r); % dt2r is the distance between the transmit antenna 2 and the receive antenna (km)
e1 = 20*log10(ft1); % ft1 is the frequency of transmit antenna 1 (MHz)
e2 = 20*log10(ft2); % ft2 is the frequency of transmit antenna 2 (MHz)
L1 = PC + d1 + e1; % Propagation loss between transmit antenna 1 and the receive antenna (dB)
L2 = PC + d2 + e2; % Propagation loss between transmit antenna 2 and the receive antenna (dB)
Gr = ; % The receive antenna gain (dB)
PA1 = ERPt1 - L1 + Gr; % Power available at receive antenna due to transmit antenna 1 (dBm)
PA2 = ERPt2 - L2 + Gr; % Power available at receive antenna due to transmit antenna 2 (dBm)
ToI = 2 * PA1; % This is required for third order intermodulation distortion (IMD) (i.e. 2ft1 - ft2 or 2ft2 - ft1) which is the most problematic form of IMD due to its occurrence adjacent to the tuned signals and its creation of `'spectral regrowths`' which obscure the signals of interest (dBm)
IC = -93; % Receiver intermodulation constant
PFS = ((abs(ft1-fr))/fr)* 100; % Percentage of frequency separation between the transmit antennas where fr is frequency of the receive antenna
alpha = 60*log10(PFS); % This is related to receive antenna's selectivity, more specifically it is the ratio of its 60 dB to 3 dB bandwidth. Either 0 or 60*log10(PFS) should be used, depending on whichever one is larger
EIP = ToI + PA2 + IC - alpha; % Equivalent Intermodulation Power (dBm)
RxS = ; % Receiver sensitivity (dBm)
ADRxS = ; % Allowable degradation of the sensitivity of the receive antenna (if any, otherwise it is 0) (dB)
P_R = RxS + ADRxS; % Receiver susceptibility (dBm)
IM = EIP - P_R % Interference margin (dB)