The exclusive-OR gate performs modulo 2 addition of its inputs.
When you cascade q two-input exclusive-or gates, with the output of the first one feeding one of the inputs of the second one, the output of the second one feeding one of the inputs of the third one, etc., the output of the last one in the chain is the modulo-two sum of the q + 1 inputs. This could be used as a parity detector.
Path loss = 20 log (4 * pi * r / lambda)
[Note: use log base 10]
where,
Path loss = signal attenuation. Unit: dB
pi = 22 / 7
r = distance between transmitter and receiver. Unit: m
lambda = wavelength of signal. Unit: m
Wavelength = C/f
where,
C = speed of electromagnetic waves in free space
= 299792458. Unit: m / s
f = frequency of signal. Unit: Hz
Let r = R * (2 ^ x)
Path loss = 20 log (4 * pi * R * L / lambda)
= 20 log (4 * pi * R / lambda) + 20 log (2 ^ x)
= 20 log (4 * pi * R / lambda) + 6x
The above derivation implies range(R) doubles every 6dB of path loss.
The path loss is +8.519dB more over a given range for the 2.4 GHz compared to 900MHz for the same range. In other words operating at 900 MHz exhibits a significantly longer range than is possible at 2.4 GHz.
Applied Electronics Journal 