Superheterodyne Receiver Questions and Answers

Answer: C

The correct pairing is A-P, B-Q, C-R. A series padder dominates where the tuning capacitance is largest, a parallel trimmer where it is smallest, and the intermediate frequency transformer works at a fixed frequency so its alignment affects every station equally. Knowing which adjustment acts where is what turns an alignment from guesswork into a short, ordered procedure.

Answer: D

The order is 1, 2, 3, 4: preselector, mixer, intermediate frequency amplifier, detector, with the audio stages following. Each position is forced by function - selection must precede conversion, conversion must precede the fixed-frequency gain, and demodulation comes last because it discards the carrier. A block diagram whose order can be reconstructed from the reasons for it does not have to be memorised.

Answer: A

The first three are correctly paired and the fourth is not, so three match. Distortion appearing only on strong signals indicates overload - too much gain reaching a stage, or gain control failing to reduce it - whereas insufficient gain would show as poor sensitivity on weak signals instead. Noticing that a proposed cause predicts the opposite dependence on signal strength is enough to rule it out without any measurement.

Answer: B

With a tuning range reaching 30 MHz, a low first intermediate frequency would place the image impossibly close to the wanted signal, so the 45 MHz first stage handles the image while the 455 kHz second stage provides the sharp filtering. Conversion gain and oscillator range are real considerations but neither forces two conversions. And filters are not asked to cover the tuning range, since the intermediate frequency is fixed. Reading a specification table means asking what each value is there to buy.

Answer: C

Heterodyning is combining two frequencies in a non-linear device so that their sum and difference appear, and the prefix super in superheterodyne indicates that the difference chosen lies above the audio range. Amplification changes amplitude rather than frequency. Envelope detection is demodulation. And sideband suppression is a filtering operation in a transmitter. Reading a technical term back to its literal meaning often recovers the idea the name was coined to express.

Answer: D

455 kHz is the long-established standard for broadcast AM, chosen as a compromise between image rejection and the ease of narrow filtering. 10.7 MHz is the FM broadcast standard, higher because FM channels are far wider and further apart. 38 kHz is the stereo subcarrier. And 45 MHz belongs to a communications receiver's first conversion. Each standard value exists because of the service it serves, and the values are worth associating with their services rather than learning as a bare list.

Answer: A

10.7 MHz is standard for FM broadcasting, and it has to be high because the signal itself occupies about 200 kHz and the channels are widely spaced. 455 kHz belongs to AM. 19 kHz is the stereo pilot. And 70 MHz is a satellite convention. The pattern is consistent: the intermediate frequency chosen rises with the bandwidth the service needs, since narrow filtering matters less when the channel is wide.

Answer: B

Sensitivity is the smallest input that produces a stated output at a stated signal-to-noise ratio, and it follows from the noise figure and the noise bandwidth together. Adjacent channel rejection is selectivity. The largest tolerable signal is the overload point or dynamic range. And output constancy describes automatic gain control. Four distinct specifications, each answering a different question about the receiver, and quoting one where another is meant is a common source of confusion.

Answer: C

Selectivity is the ability to accept the wanted channel while rejecting its neighbours, and in a superhet it is set almost entirely by the intermediate frequency filter. The weakest usable signal is sensitivity. The range of levels handled is dynamic range or gain control range. And dial accuracy is calibration. Pairing each specification with the block that determines it turns a list of terms into a working model of the receiver.

Answer: D

Dynamic range is the span between the noise-limited weak end and the distortion-limited strong end, so it depends on the noise figure at one extreme and linearity at the other. Gain variation across the band is a tracking matter. The frequency difference is the intermediate frequency. And an audio-to-radio power ratio is not a meaningful specification. A range bounded by two different physical limits is improved only by attacking whichever limit is closer, which is why it resists simple fixes.