RCSE
Radio Communication Systems Quiz
Test your knowledge on radio communication systems with this comprehensive quiz! Covering various aspects of frequency modulation, receiver sensitivity, and radio transmitters, this quiz is designed for both beginners and experts in the field.
Key Features:
- 35 multiple choice questions
- Instant feedback for correct answers
- Enhance your understanding of radio technologies
Frequency change in radio transmitters can be performed using:
Both frequency multipliers and frequency changers
Methods other than frequency multipliers and frequency changers
Frequency changers using an auxiliary oscillator
Frequency multipliers
Considering the following affirmations regarding the direct FM transmitters (DFMT), identify the false one:
This architecture can be used if the modulating signal doesn’t have componets on too low frequencies
His architecture allows the design of transmitters with a very simple RF chain, whithout mixers, IQ modulators or IF stage
Although it was a conceived for FM signals, this architure can be successfully used also for QAM signals
It’s an architecture suitable for applications that require equipment with low power consumption, low price and low size
For the following block diagram, corresponding to a broadcasting radio transmitter you are required to choose the characteristic values for the functional blocks in order to generate a FM signal with f0=108 MHz, Δf=30kHz and P0=1W. The signal produced by the synthesizer has f1=6MHz and Δf=5kHz and the signal level after the FC is of 1mW.(n is the multiplication order, fPO2 – the frequency of the signal generated by PO2, and GPA – the power gain of the final amplifier)
N = 3, Fpo2= 72MHz, Gpa = 30dB
N = 6, Fpo2= 140MHz, Gpa = 30dB
N = 6, Fpo2= 72MHz, Gpa = 20dB
N = 6, Fpo2= 72MHz, Gpa = 30dB
If a useful signal with a level of 40 µV is transmitting on f=540 kHz, the blocking of the signal will be obtained when an interfering signal is transmitting on the 560 kHz frequency with a level of :
120dBμ
100dBμ
80dBμ
105dBμ
For a radio receiver for AM signals, working at small signal level, the measured gain limited sensitivity S A = 50 µV for a signal-tonoise ratio, measured at the output, RSZ OUT = 14 dB. The noise limited sensitivity of this radio receiver is:
100 μV
50 μV
141 μV
70.5 μV
In order to measure the selectivity of analog RR for high signal level of the input signals, the following block diagram can be used. The measurement of of the receiver blocking parameter is made using the following procedure:
The RR is tuned on the desired signal, normal modulated, generated using SSG1; a certain level is chosen for the desired signal; a perturbation signal is applied from SSG2, choosing a desired value for the frequency difference between the two signals; the perturbation signal is not modulated; the level of the perturbation signal is modified until the level of the signal measured at the output of the receiver decreases with 3 dB.The perturbation level at this moment is the receiver blocking parameter
The RR is tuned on the desired signal, normal modulated, generated using SSG1; a certain level is chosen for the desired signal; a perturbation signal is applied from SSG2, choosing a desired value for the frequency difference between the two signals; the perturbation signal is not modulated; the level of the perturbation signal is modified until the level of the signal measured at the output of the receiver decreases with 20 dB. The perturbation level at this moment is the receiver blocking parameter
The RR is tuned on the desired signal, normal modulated, generated using SSG1; a certain level is chosen for the desired signal; a perturbation signal is applied from SSG2, choosing a desired value for the frequency difference between the two signals; the perturbation signal is normal modulated; the level of the perturbation signal is modified until the level of the signal measured at the output of the receiver decreases with 10 dB. The perturbation level at this moment is the receiver blocking parameter
The RR is tuned on the desired signal, normal modulated, generated using SSG1; a certain level is chosen for the desired signal; a perturbation signal is applied from SSG2, choosing a desired value for the frequency difference between the two signals; the modulation of the desired signal is cut; the perturbation signal is normal modulated; the level of the perturbation signal is modified until the level of the signal measured at the output of the receiver decreases with 3 dB. The perturbation level at this moment is the receiver blocking parameter
The VCO injection pulling phenomenon appears because of the influence of the signal radiated from the power amplifying stage towards the low power section. Identify which affirmation is false:
VCO injection pulling can be avoided if the high power section and the low power section work on different frequencies
As a result of the VCO injection pulling, the remodulation phenomenon appears
The remodulation phenomenon reduces the band that is occupied by the modulated signal
VCO injection pulling can be limited if the local oscillator is shielded
Which one of the below affirmations is NOT true regarding the peak to average power ratio parameter?
For amplitude modulated signals is equal with 1 and for frequency modulated signals is larger than 1;
Its value has a strong impact on the efficiency with which the power amplifier can work
For amplitude modulated signals is larger than 1 and for frequency modulated signals is equal with 1
Has high values for signals with a high spectral efficiency
Amplitude modulation of a signal can be performed in:
The last power amplifying stage
Any stage located after the frequency changer
Any small level stage of the radio transmitter (oscillator, amplifier, frequency changer)
The first amplifying stage located after the pilot oscillator
The maximum area that can be covered with usable radio signal by a transmitter depends on:
Its working frequency
The transmit power
Both the transmit power and the frequency
Neither the transmit power, nor the working frequency
A radio frequency signal characterized by a wavelength of 50 cm is located in the:
UHF range
LF range
VHF range
HF range
The radiation pattern of an antenna represents:
No one of the above statements is true
A graphical representation in the plane that contains the antenna of the ratio between the density of the energy radiated by theanalyzed antenna on different directions and the density of the energy radiated by an ideal isotropic antenna on the same direction
A graphical representation, in a plane perpendicular on the antenna, of the ratio between the density of the energy radiated by theanalyzed antenna on different directions and the density of the energy radiated by an ideal isotropic antenna on the same direction
A 3D graphical representation of the ratio between the density of the energy radiated by the analyzed antenna on different directionsand the density of the energy radiated by an ideal isotropic antenna on the same direction
Let’s consider a radio communication system that works on the 10 GHz frequency and has a transmitter power of 20 dBm. The antennas are directly connected to the output of the transmitter and to the input of the receiver. The two antennas have each 10 dB gain, are placed in line of sight and the attenuation for the free-space propagation can be approximated using the relation:
Pr= - 92,4 dBm
Pr= - 112,4 dBm
Pr= - 52,4 dBm
Pr= - 72,4 dBm
The gain limited sensitivity, defined for analog radio receivers, represents the minimum level of the input signal for which at the output a signal having a standard power is obtained, in the following conditions:
RR is tuned on the central frequency of the useful signal, the volume is in the maximum position, the tone is in the median position,the signal to noise ratio is having a standard value
RR is tuned on the central frequency of the useful signal, the volume is in the median position, the tone is in the median position, thesignal to noise ratio can have any value
RR is tuned on the central frequency of the useful signal, the volume is in the maximum position, the tone is in the maximumposition (high frequencies), the signal to noise ratio is set at the optimal value
RR is tuned on the central frequency of the useful signal, the volume is in the maximum position, the tone is in the median position,the signal to noise ratio can have any value
Analyze the following affirmations regarding the AGC system: A1. The level of the signal that reaches the antenna of any RR can vary in very wide limits (dynamic range); A2. The AGC system was conceived in order to maintain the level of the signal from the output of the RR as high as possible; You are required to decide if:
Both affirmations are true
The A1 affirmation is true and the A2 affirmation is false
Both affirmations are false
The A1 affirmation is false and the A2 affirmation is true
An important parameter for radio receivers is the dynamic range. Select the action which cannot influence the dynamic range of a radio receiver:
Using very performant band pass filters
Increasing the sensitivity of the radio receiver
Using functional blocks for which the non-linear phenomenons appear at very high level of the processed signald. Using low-noise amplifiers with a very low noise factor
Let’s consider a radio receiver for broadcasting radio transmissions in the band 150 - 280 kHz. The block diagram specific for measuring the sensitivity and the selectivity is used. The power levels of the input and out signals are measured. The following values are obtained: gain limited sensitivity: -70dBm, output noise level: -17dBm. The noise limited sensitivity of the RR is:
S ≈ - 68 dBm
S ≈ - 84 dBm
S ≈ - 94 dBm
S ≈ - 78 dBm
Which one of the following parameters cannont be considered a specific parameter for a radio communication system:
Necessary bandwidth
Allocated bandwidth
Noise bandwidth
Occupied bandwidth
The following functions have to be realized in a radio transmitter: Generation and processing of the carrier signal; Generation of the modulating signal; Rejection of the signals coming from other radio transmitters; The final processing of the modulating signal, necessary in order to adequately perform the modulation process; v. Achieving the modulation; Modulated signal processing; Converting the modulated signal in EMW; The following affirmations are true:
I, iv, v, vi, vii
I, ii, iii, iv, vi
I, ii, v, iii, vii
Ii, iii, v, vi, vii
By using radio communication systems radio communication services can be offered. Some examples are: I. Radio broadcasting services Mobile communication services Fixed services Wired LAN internet access services Operation and maintenance network services Radio communication services are:
I, ii, iii
Ii, iii, v
I, ii, v
Iii, iv, v
Which affirmation regarding the L matching circuit is NOT true:
S the simplest type of matching circuit
It doesn’t allow the control of the quality factor
It can provide the matching only if the optimal PA resistance is smaller than the antenna input resistance
It can provide the matching only if the optimal PA resistance is larger than the antenna input resistance
The radio network necessary for gathering the information from several sensors placed in a home environment in a local server is a: Select one:
Broadcasting network
Point-to-multipoint network
Point-to-point radio link
Data collecting network
In case of RR for digital transmissions the concept of receiver blocking is used. The definition of the concept is:
The phenomenon through which the reception of the desired signal is affected by an increase in the bit error rate, because of the presence of one or several radio signals corresponding to some channels located quite far away, in the frequency domain, from the desired channel
The phenomenon through which the reception of the desired signal is affected by an increase in the bit error rate, because of theincrease of the thermal noise from the radio channels located quite far away, in the frequency domain, from the desired channel
The phenomenon through which the reception of the desired signal is affected by an increase in the bit error rate, through the total orpartial blocking of one or several signal processing stages located after the demodulator
The phenomenon through which the reception of the desired signal is affected by an increase in the bit error rate, because of themodification of the local oscillator frequency because of the signal sent by the pair transmitter, which uses the same antenna
Identify the correct affirmation regarding the Dual-Port Direct FM transmitters (DD-FMT) represent:
It’s an architecture suitable in case of modulating signals that don’t contain components at very low frequencies (around DC)
The modulating signal is applied to a distributor who sends the low frequency components to a VCO and the high frequency ones toa programmable divider.
The modulating signal is applied to a distributor who sends the high frequency components to a VCO and the low frequency ones toa programmable divider
The effect of the programmable divider is a high pass one
The specific of radiocommunication systems is that:
They use twisted pairs and modulated sine signals for transmitting the information
They don’t use modulated sine signals for transmitting the information
They use the propagation of the electromagnetic waves for transmitting the information
They use random signals for transmitting the information
In order to perform the matching of an antenna having an input resistance Ra=50 Ohm, to the final stage of a radio transmitter having a optimal resistance R0=50 Ohm, a PI matching network is used. The imposed minimum attenuation of the second harmonic of the carrier signal is of 30 dB. The virtual resistance RI has to have a value of:
2.5 ohm
10 ohm
1 ohm
5 ohm
Identify the false affirmation regarding the modulation track-out effect:
It is a phenomenon that has to be considered in case of direct FM transmitters (DFMT)
It manifests by the cancelling of the modulation which is produced using a PLL frequency synthesizer for very low frequencycomponents in the spectrum of the modulating signal
It is a phenomenon that has both negative and positive aspects
It manifests by the cancelling of the modulation which is produced using a PLL frequency synthesizer for very high frequencycomponents in the spectrum of the modulating signal
When choosing the working regime for a power amplifier implemented using bipolar transistors the behavior of the different classes has to be taken into account. Considering the following affirmations: The A-class amplifying stages have low efficiency, but they can be used to process signals having a variable envelope The C-class amplifying stages have high efficiency, but work in a non-linear regime, so they don’t preserve the modulation carried by the envelope of modulated signals.
I is false and II is false;
is false and II is true;
I is true and II is false;
I is true and II is true;
The following affirmations are made: A1. Sensitivity defined for radio receivers (RR) used in digital transmissions and denoted with Sa represents the level of the input signal when the RR is tuned on the working channel and at the input of the detector a usable signal is obtained; A2. The measurement is performed considering that at the input of the RR several interfering signals are applied; Decide if:
Both affirmations are false
Both affirmations are true
A1 is false, A2 is true
A1 is true, A2 is false
Let’s consider a transimtter with an output power of 50dBm and an transmit antenna having a gain of 10dB. The equivalent isotropically radiated power (EIRP) is:
100W
1000W
500W
200W
For measuring the sensitivity of a RR used in digital transmissions the following block diagram can be used. Regarding this diagram and the measurement procedure the following can be said:
Block 1 represent a modulated radio signal generator and 2 is an equipment which generates the modulating signal as a random data sequence; this equipment can compare the modulating sequence with the data sequence obtained at the output of the RR; For the measurement the frequency of the signal produced by the generator is adjusted on the channel neighboring to the one on which the RR -3 works; the signal level is modified until the bit error rate (BER) is equal with 10 , irregarding the application; the level obtained is this way is the RR sensitivity
Block 1 represent a modulated radio signal generator and 2 is an equipment which generates the modulating signal as a random data sequence; this equipment can compare the modulating sequence with the data sequence obtained at the output of the RR; For the measurement the frequency of the signal produced by the generator is adjusted on the channel neighboring to the one on which the RR works; the signal level is modified until the bit error rate (BER) is equal with the one imposed by the application; the level obtained is this way is the RR sensitivity
Block 1 represents a standard signal generator and 2 is an equipment which generates the modulating signal as a sine signal; this equipment can compare the modulating sequence with the data sequence obtained at the output of the RR; For the measurement the frequency of the signal produced by the generator is adjusted on the channel on which the RR works; the signal level is modified until the nonlinear distortions coefficient is equal with the one imposed by the application; the level obtained is this way is the RR sensitivity
Block 1 represents a modulated radio signal generator and 2 is an equipment which generates the modulating signal as a random data sequence; this equipment can compare the modulating sequence with the data sequence obtained at the output of the RR; For the measurement the frequency of the signal produced by the generator is adjusted on the channel on which the RR works; the signal level is modified until the bit error rate (BER) is equal with the one imposed by the application; the level obtained is this way is the RR sensitivity
Affirmation (A) : the short wave range (SW) is not so often used for radio broadcasting. Explanation (E): because of the existence of some waves reflected by the ionosphere a fading phenomenon appears, which affects the quality of the reception.
Both affirmations are true, and E is the explanation for A
A is not true but E is true
Both affirmations are true, but E is not the explanation for A
A is true but E is not true
The equivalent isotropically radiated power (EIRP) is calculated:
Using the power that is applied at the input of the transmit antenna and the antenna gain
Using the power that is applied at the input of the transmit antenna and the attenuation caused by the propagation
Using other parameters
Using the power that is applied at the input of the transmit antenna and the antenna losses
Let’s consider the following affirmations: A1. A receiver can adequately process the desired signal, even if on the same frequency a perturbation signal exists, if between the two signals a level difference of N dB exists. A2. The N dB value corresponds to the co-channel rejection factor, which, as absolute value, represents the maximum value with which the desired signal has to be greater than the perturbation signal, for a correct reception of the desired signal; It can be noticed that:
A1 is true and A2 is false
Both affirmations are false
A1 is false and A2 is true
Both affirmations are true
The performance of a digital radio communication system can be evaluated using:
The bit error rate
The transmission range
The average squared error
The signal to noise ratio
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