Re:New LoRa RF distance record: 1336 km / 830 mi
by drmpeg on Friday September 08, 2023 @07:06AM
(#37432052)
No, there's very little loss from the atmosphere at 432 MHz. The 390 dB figure is a misunderstanding of how the path loss is calculated. The poster "wl" took the one way path loss (195 dB) and doubled it. But the moon is a huge reflector and provides "gain".
Here's a C program with the correct equation.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(int argc, char **argv)
{
double d, f, lambda, loss;
if (argc != 3) {
fprintf(stderr, "usage: moon <km> <frequency(MHz)>\n");
exit(-1);
}
d = atof(argv[1]) * 1000.0;
f = atof(argv[2]);
lambda = 299792458.0 / (f * 1000000.0);
loss = (0.065 * (1.738e6 * 1.738e6) * (lambda * lambda)) / (631.65468167 * (d * d * d * d));
printf("EME path loss = %f dB\n", 10 * log10(loss));
return 0;
}
1.738e6 is the radius of the moon in meters and 0.065 is the reflection efficiency.Satellites make moonbounce impracticable.
As an aside, would radio via the moon ever be practical? Without pumping out so much transmit power that you pick up the signal anyway, without pointing a receiver at the moon. I think it would be neat, if only for the sake of novelty.