1. In a radio receiver, which of the following stages does not need alignment _____
TRF stage
IF stage
Antenna input stage
Audio stage
Answer.4. Audio stage
Explanation
Alignment is a process where several stages of the receiver are properly tuned to the desired frequency.
The input to the audio stage is a demodulated message signal and does not require any alignment to receive the desired frequency.
In electronics, a super-heterodyne receiver uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency and the audio stage does not need alignment in a radio receiver.
2. Which of the following is the earliest type of AM receiver?
Tuned Radio Frequency (TRF) Receiver
Regenerative Receiver
Decoherer Receiver
None of the above
Answer.1. Tuned Radio Frequency (TRF) Receiver
Explanation
The tuned radio-frequency (TRF) receiver was one of the earliest types of AM receivers. TRF receivers are probably the simplest designed radio receiver available today.
3. The stages of TRF receiver include
RF stage
Detector Stage
Audio stage
All of the above
Answer.4. All of the above
Explanation
TRF receiver includes 3 stages i.e an RF stage, a detector stage, and an audio stage. Generally, two or three RF amplifiers are required to filter and amplify the received signal to a level sufficient to drive the detector stage.
The detector converts RF signals directly to information, and the audio stage amplifies the information signals to a usable level.
4. The main disadvantage of a TRF receiver is
Inconsistent Bandwidth
High Instability
Non-uniform Gain
All of the above
Answer.4. All of the above
Explanation
Although TRF receivers are simple and have a relatively high sensitivity, they have three distinct disadvantages that limit their usefulness to single-channel, low-frequency applications.
Inconsistent Bandwidth:- The primary disadvantage is their bandwidth is inconsistent and varies with center frequency when tuned over a wide range of input frequencies. This is caused by a phenomenon called the skin effect. At radio frequencies, current flow is limited to the outermost area of a conductor; thus, the higher the frequency, the smaller the effective area and the greater the resistance.
Instability:- The second disadvantage of TRF receivers is instability due to the large number of RF amplifiers all tuned to the same center frequency. High-frequency, multistage amplifiers are susceptible to breaking into oscillations. This problem can be reduced somewhat by tuning each amplifier to a slightly different frequency, slightly above or below the desired center frequency.
Non-uniform Gain:- The third disadvantage of TRF receivers is their gains are not uniform over a very wide frequency range because of the nonuniform L/C ratios of the transformer-coupled tank circuits in the RF amplifiers.
5. The main advantage of TRF receiver is
Simplicity
High sensitivity
Both 1 and 2
None of the above
Answer.3. Both 1 and 2
Explanation
The main advantage of a TRF receiver are:
1. Simplest type of receiver since it does not involve mixing and IF operation.
2. Very much suitable to receive a single frequency.
3. TRF receives have good sensitivity.
6. A RF carrier of 700 kHz at 10 V peak value is amplitude modulated by an audio signal of 2 kHz at 5 V. The sidebands produced are:
702 kHz
698 kHz
702, 698 kHz
72 kHz
Answer.3. 702, 698 kHz
Explanation
The sideband frequencies are fc ± fm = (700±2) KHz
∴ The sidebands produced are: 702, 698 kHz
7. To improve selectivity, the bandwidth of a receiver can be reduced by which of the following methods?
Using fewer tuned circuits
Using a loudspeaker
Adding more gain
Using more tuned circuits
Answer.4. Using more tuned circuits
Explanation
Selectivity is the measure for the receiver to check the desired signal is captured at the output or not.
Receiver bandwidth should match with the modulating signal for better sensitivity.
in digital systems, the minimum theoretical bandwidth is Nyquist bandwidth.
The selectivity of a receiver is evaluated by the relative intensity of a signal received from an external source.
Tuned circuit
This is defined as any electrical conducting path between the Inductor and Capacitor. The circuit consists of both the elements as inductor and capacitor.
Simultaneous variation of multiple frequencies is not possible with the tuned circuits. To determine the suppression factor IRR (Image Rejection Ratio) is used.
