# Longley Rice propagation model and reciprocity

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Joel Johnson on 9 Oct 2021
Commented: Joel Johnson on 14 Oct 2021
Code snippet below seems to show that MATLAB's Longley-Rice propagation model may not always be reciprocal - is this correct? Thanks!
close all; clear all;
% A test to show that the Matlab LR functions don't seem to be reciprocal
pm = propagationModel('longley-rice','AntennaPolarization','vertical');
freq = 469e6; % Tx freq (MHz)
S1 = [39.420200,-82.875300]; % Lat/Lon of Site 1
S2 = [39.413000,-82.896111]; % Lat/Lon of Site 2
s1ht = 1:50; % Antenna height @ site 1
s2ht = 2.08; % Antenna height @ site 2
% Link from S1 to S2
tx = txsite('Latitude',S1(1),'Longitude',S1(2),'AntennaHeight',s1ht,'TransmitterFrequency',freq);
rx = rxsite('Latitude',S2(1),'Longitude',S2(2),'AntennaHeight',s2ht);
PL1 = pathloss(pm,rx,tx);
% Now reverse the link
tx = txsite('Latitude',S2(1),'Longitude',S2(2),'AntennaHeight',s2ht,'TransmitterFrequency',freq);
rx = rxsite('Latitude',S1(1),'Longitude',S1(2),'AntennaHeight',s1ht);
PL2 = pathloss(pm,rx,tx);
plot(PL1,s1ht,'linewidth',2); set(gca,'Xdir','Reverse'); set(gca,'Fontsize',20); xlabel('Path loss (dB)'); ylabel('Tx Antenna height (m)')
hold on
grid on
plot(PL2,s1ht,'x','linewidth',2);
legend('S1 to S2','S2 to S1')
##### 1 CommentShowHide None
Joel Johnson on 9 Oct 2021
I subsequently noticed that there is no difference in the two in R2021b so probably this got fixed somewhere between R2018 and R2021.

Tanmay Das on 14 Oct 2021
Hi,
As pointed out by Joel, the bug has been fixed in the future releases. So it is recommended to update the MATLAB version in order to leverage its full functionality.
##### 1 CommentShowHide None
Joel Johnson on 14 Oct 2021
Thanks!

R2018b

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