5.4 Practice Problems

1) For an AM DSBFCwave with a peak unmodulated voltage of 10 V and a load

resistance of 100, the glven modulation index is 0.5. Determine the

following:

a) The carrier and the sideband power

b) The total power

c) The percent power of the information

d) The power spectrum

2) Calculate the percentage power saving when the carrier and one of the

sidebands is suppressed in an AM signal if the modulation index is a) 100%

and b) 25%.

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LESS (Clf.J 5 5IA'L'JLe, S l.d~{)1A//lA~_,,):,r,;te.-Yli-'"-'._Dl~IfSI.u:.~~t"".,ftf.;~~~:m~~;>Ij,~iIj".>'~iJ~~~~"~;~~~wi.I..-.u~:.~~ii:Q;;ii.ifr:ii

3) For a SOO--Wcarrier modulated to -3 depth of gOq~JI find tile total power ano

the ~1op.s in each of the follmving forms of /,.,ivL

a) BE

b) H3E

c) DSB

----------------------------------------

---------,--------

------------------------------_._-----------

4) An A~'"wave has a totai transmitted power of 4 kW when modulated at 85%.

How much total power should an SSBwave contain in order to have the same

power content as that in the two sidebands?

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5) If a transmitter power of 100 W is sufficient for reliable communication over acertain path using the SSB, approximately what power level would be required

using the H3E?

6) What is the maximum modulating signal frequency that can be used in a J3E

system with a SO-kHz bandwidth?

7) A filter-type, SSB generator uses an ideal bandpass filter. with a center

frequency of 5.000 MHz and a bandwidth of 2.7 kHz. What frequency should':..,

be used for the carrier oscillator if the generator is to produce a LSB signal

with a baseband frequency response having a lower limit of 280 Hz?

8) An SSBSC signal has a suppressed carrier frequency of 2MHz. It is modulated

with two audio tones having frequencies of 1500 and 2200 Hz. The receiver is

mistuned so that the BFO is at 1.9995MHz. What will be the output

frequencies of the demodulator if the signal is LSB?

95

9) A J3E transmitter operating at 16 MHz has a frequency stability of 1 part per

million. If its transmission is reproduced by a receiver whose frequency

stability is 8 parts per million, what is the maximum frequency error of the

output of this receiver in reproducing this transmission?

10) The CB radio was developed using a full-carrier DSB AM. It operates using

40 channels, each 10 kHz wide. When the SSBSCis used, the same carrier

frequencies are used as with the conventional AM, but the transceivers are

switchable to either a lower or an upper sideband. How many channels are

available when the SSB is used?

11) What is the power saving of a double sideband full carrier AM signa! at 50%

modulation, if the emission used is J3E?

96

12) What is the maximum modulating signal frequency that can be used with a

H3E system with 50-kHz bandwidth?

13) An AM transmission 1000W is fully modulated. Calculate the power

transmitted if it is transmitted as a SSBsignal.

14) A SSB transmission drives llO-Vpk into a 75-0 antenna. Calculate the PEP.

15) An SSB transmitter has a PEP10 kW, what is the average power?

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ZNX'

6.5 Practice Problems

1) A TRF receiver. is to be designed with a single tuned circuit using a 20-/-lH

inductor.

a) Calculate the capacitance range of the variable capacitor required to

tune from 535-1605 kHz.

b) The ideal 10-kHz bandwidth is to occur at 1000kHz. Determine Q.

c) Calculate the bandwidth of this receiver at 535 kHz and at 1605 kHz.

2) For an AM receiver that uses high-side injection and has a local oscillator

frequency of 1455 khz, determine the IF carrier upper side frequency and

lower side frequency for an RF signal that is made up of a carrier, an

upper and a lower side frequencies of 1000 kHz, 1005 kHz, 995 kHz,

respectively. .

108

3) A receiver tunes the 300 kHz to 3 MHz MF band in one range, using an IF

of 35.75 MHz. Calculate the range of oscillator frequencies and the range

of image frequencies.

4) What is the local oscillator frequency range in the commercial AM

broadcast if the IF is equal to 455 kHz?

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U'5lU1iiW _ -5) Determine the image frequency of a broadcast band receiver using a 455

kHz IF tuned to 630 kHz - DZfvlM.

6) Determine the local oscillator frequency of a broadcast band receiver

using a 455-kHz IF tuned at 630 kHz.

-------------_._-

.--------------- ---

7) For a receiver with IF~ RF, and local oscillator frequencies of 455 kHz, 630

kHz and 1085 kHz, respectively, determine the:

a) image frequency.

b) IFRR for a pre-selector Q of 80.

---------_._._------_ ..__ ._---- -.----

-------_._._------_._--

-----_. ------.--.~-~---.----.-------------,--.-..-----.-.----.----.----------~-- .....-

8) A superheterodyne receiver is tuned to a frequency of 10 MHz when the

local oscillator frequency is 12.5MHz.

a) What is the IF?

b) Which type of injection is in use?

9) One receiver has a sensitivity of 1 /-LV and another has a sensitivity of 10-

dBf under the same measurement conditions. Both receivers have an

input impedance of 750. Which receiver is more sensitive?

10)A receiver has a sensitivity of 0.75 ~V and a blocking dynamic range of

80 dB. What is the strongest signal that can be present along with a

O.75-~V signal without any blocking/desensitization taking place?

111

11) For an AM receiver tuned to a station at 590kHz with IF=455 kHz,

calculate the image frequency rejection in dB. Assume that the input filter

consists of one tuned circuit with a Q of 40.

12) A superheterodyne receiver having an RFamplifier and an IF of 10.6 MHz

is tuned to 90.7MHz. Calculate the Q's of the RF and mixer input tuned

circuits, both being the same, if the receiver's overall image rejection is to

be 100.

13) Determine the net receiver gain for an AM receiver with an RF input

power of -88 dBm and an audio signal of 12 dBm

-------

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14) A receiver for a signal at 150 MHz uses a iO.7-MHz IF and low tracking.

Calculate the LO frequency and the image frequency.

15) A receiver intended for the aircraft to control tower signals at 110 MHz

uses double conversion, with 10.7 MHz and 455-kHz IFs. Calculate the

following if the receiver employs low tracking: a) LO frequencies, b)

frequencies after using the 1st mixer, c) output of the 2nd mixer, d)

image frequency.

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