Data Sheet
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395. FM Transmission Power
Build the circuit above, turn on the switch (62) and you will hear some FM radio stations from the
speaker (93) and the colorful LED (72) will light. You may have to press one of the press switches (61)
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.
As discussed in the previous project, over-the-air propagation losses are huge even at relatively low
frequencies like 88-108MHz. In order to overcome this, radio stations transmit with very high power.
Some radio stations may transmit up to 50kW (this is radiated power from the FM tower antenna).
Based on the calculation in the last project, this means that the signal strength when it arrives at the
car antenna would be 50,000/35,096,763 = 0.0014 or 1.4mW. Fortunately, FM receivers can use
ltering and amplication to recover, demodulate and play out the FM signal even at these low powers.
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