563489578934

Problems 663
8–10 A digital TV station transmits on Channel 7 with an ERP of 18 kW. The signal from this TV
station is received 50 miles away via a LOS path with a receiving antenna that has a gain of 8 dB
on Channel 7. Calculate the power at the receiving antenna output-connector in:
(a) dBm units.
(b) in dBmV units across a 75 Ω load.
(c) in mV across a 75 Ω load.
8–11 Rework Prob. 8–10 if the TV station operates on Channel 42.
8–12 A digital TV station operates on Channel 7 and another digital TV station operates on Channel 51.
Using MATLAB, plot the free-space loss (in dB) for the Channel 7 station as a function of distance
in miles. Repeat the plot for the Channel 51 station. Compare these two results by plotting them on
the same figure. Do these losses change if these are analog TV stations instead of digital?
8–13 Using MATLAB, plot the free-space loss in dB as a function of distance in miles for a cellular
link at 850 MHz. Also, plot the LOS loss for a cellular link at 1900 MHz. Compare these two
results by plotting them on the same figure. Comparing these two plots, which link costs the
cellular company less to operate for the same cell-site coverage area?
★ 8–14 Using MATLAB, plot the PSD for a thermal noise source with a resistance of 10 kΩ over a frequency
range of 10 through 100,000 GHz where T = 300 K.
8–15 Given the RC circuit shown in Fig. P8–15, where R is a physical resistor at temperature T, find the
RMS value of the noise voltage that appears at the output in terms of k, T, R, and C.
R
C
V rms =?
Figure P8–15
8–16 A receiver is connected to an antenna system that has a noise temperature of 100 K. Find the
noise power that is available from the source over a 20-MHz band.
★ 8–17 A bipolar transistor amplifier is modeled as shown in Fig. P8–17. Find a formula for the available
power gain in terms of the appropriate parameters.
i
Transistor model
R s
E s
h ie h fe i
1
R=––
h oe
R L
Figure P8–17