Data Sheet

394. Pathloss Calculation
Build the circuit above, put the reed switch (83) across points A and B and turn on the switch (62).
You won’t hear any radio stations from the speaker (93) until you place the magnet (7) near the reed
switch (83). You may have to press the press switch (61) connected to CH– to get the FM receiver to
scan for a channel. For best FM reception, hold the open end of the spring wire (9) in the air.
The previous projects discussed the propagation characteristics of radio waves and provided a formula
for pathloss. To give you an idea of just how much pathloss is typical, consider trying to receive an FM
radio station with your car antenna 1 mile (~1609 meters) away from the FM transmission antenna.
Assuming you had line-of-site transmission (no trees or buildings between the antennas) and were
using FM channel 200 at 87.9 MHz, the free space pathloss formula says there will be a pathloss of
approximately (4*3.1416*1609*87.9x10
6
/3x10
8
)
2
= 35,096,763 or about 75 dB. That’s a huge
pathloss!
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