Radio links Seminary 7

Problem 7.1 Free space (one way / line-of-site) propagation a) Calculate the section attenuation of a 10 km long radio link operating on 450 MHz frequency and the receiver’s and transmitter’s antenna gain are both 20 dB. b) What is the receiver’s input voltage if the transmitter’s output power is 1 W and the input impedance of the receiver is 50 Ω?

Problem 7.2 Ground backscattered (two way) propagation The antenna of the transmitter of a 10 km long radio link is mounted 20 m over the ground level, while the receiver’s antenna is on 10 m height and both antennas have a gain of 10 db. a) What is the operating wavelength/frequency if we either grow or diminish the antenna height the received power is always dwindling? b) Determine the section attenuation if the ground backscatter is -1.

The two-way propagation model

(1–|Γ|) 2 1 (1+|Γ|) 2 |z(Δ)| 2 =P R2 /P R1 r zone of interference

The received power vs. the distance

Problem 7.3 Two way propagation with no total ground backscatter We plant a receiver 3 km away from a transmitter broadcasting a 450 MHz radio signal. By changing the height of the receiver’s antenna, the received signal is changing between 10 and 90 pW. If the change is 5 m, the received signal returns to the original. a) What is the ground reflection coefficient? b) How high the transmitter antenna is mounted?

Problem 7.4 Satellite communications a) What is the gain of a dish of 110 cm in diameter receiving a 12 GHz direct broadcast satellite (DBS) signal? b) How exactly should the above antenna be adjusted to the satellite direction? c) What should be the gain of the transmitter’s antenna on the DSB if want to broadcast over an area of 2000 km in diameter on Earth’s surface.