Down-converting the operating frequency to a lower Intermediate Frequency facilitates selectivity: for example, 0.6% of 455 kilohertz is 2.7 kHz, 0.6% of 3.7 megahertz is 22 kHz.
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Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The Intermediate Frequency chain is responsible for most of the selectivity. Crystal filters or mechanical filters can be used at the Intermediate Frequency. Digital Signal Processing (DSP) is used in modern receivers.
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Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The first conversion to a high IF places the image frequency far away from the operating frequency so it can be optimally rejected by the front-end filtering. The second conversion to a low IF performs the traditional function of ensuring selectivity to protect the receiver from adjacent channels.
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The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain.
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In a superheterodyne receiver, injection from the Local Oscillator can be above or below the operating frequency. There could be two answers: Local Oscillator minus Intermediate Frequency or Local Oscillator plus Intermediate Frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to "reinsert the carrier" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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In a superheterodyne receiver, injection from the Local Oscillator can be above or below the operating frequency. There could be two answers: Intermediate Frequency plus operating frequency or Intermediate Frequency minus operating frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to "reinsert the carrier" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Oscillators need to be free of drift regardless of voltage and temperature variations or mechanical vibrations. Spectral purity is the absence of harmonics, other spurious oscillations or noise; purity limits spurious responses in the subsequent mixing processes.
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Two stages may require tuning ahead of the Intermediate Frequency amplifier: the preselector and the high-frequency oscillator, commonly known as the Local Oscillator. As the question alludes to one trimmer and one inductance, only one circuit can be tuned.
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The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Through an elimination process, only one answer makes sense. The input and the output of the radio-frequency amplifier run at the operating frequency. The output of the RF amplifier constitutes the input to the Mixer.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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A receiver's "Noise Floor" is the power level at which an incoming signal exhibits a Signal-To-Noise ratio of zero decibel: that is, the signal power equals the internal noise power level. Noise Floor is evaluated while measuring "Minimum Discernible Signal (MDS)". The "Noise Figure" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver.
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The Intermediate Frequency chain is responsible for the selectivity and a large part of the gain. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver.
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The Radio-Frequency Amplifier should only introduce enough gain to override the internal noise of the subsequent Mixer. Too much gain will degrade Dynamic Range; Dynamic Range is broadly defined as a ratio between the strongest signals that can be tolerated near the passband and the "Minimum Discernible Signal".
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The Intermediate Frequency chain is responsible for the selectivity and a large part of the gain. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver.
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The SINAD (signal + noise + distortion over noise + distortion) ratio takes the SNR (signal + noise over noise ratio) one step further by including distortion. A 12 dB SINAD ratio ensures that speech remains intelligible. Sensitivity expressed in those terms is the lowest RF level that will produce a usable message. The RF signal generator must be calibrated so the number of microvolts is precisely determined. Total Harmonic Distortion compares unwanted harmonic components added to the desired fundamental frequency, an audio tone in this instance.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Dynamic Range is broadly defined as a ratio between the strongest signals that can be tolerated near the passband and the "Minimum Discernible Signal". The "Noise Figure" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The "Noise Figure" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The "Noise Figure" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Below 30 megahertz, the antenna picks-up atmospheric noise and man-made noise at levels far more important than internal noise. As the frequency of operation rises, those types of noise become less prevalent. On Ultra High Frequencies (UHF) and above, the internal noise becomes the limiting factor in receiving weak signals. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver: for weak signal work on 2 metres and up, more attention must be placed on reducing internal noise in the front-end.
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Dynamic Range is broadly defined as a ratio between the strongest signals that can be tolerated near the passband and the "Minimum Discernible Signal". Other related notions include Blocking Dynamic Range and Intermodulation Dynamic Range. Blocking Dynamic Range measures how much of a single strong off-channel signal can be tolerated while receiving a weak signal, it is a measure of desensitization or immunity to overload. Intermodulation Dynamic Range verifies how strong two off-channel signals can be without spurious responses being generated in the receiver, it is a measure of resistance to intermodulation.
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A preselector is a tuned stage which passes a desired range of signals to a receiver: it ensures a certain preliminary selection. It may or may not be amplified; in other words, active or passive.
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With "true" FM, deviation is independent of modulating frequency, actual deviation is determined solely by the modulating amplitude. With Phase Modulation, deviation depends on the amount of phase shift and its rapidity, increasing modulating frequency results in proportionally more deviation even if amplitude is held constant. Because commercial standards were based on Phase Modulation, an FM transmitter requires an artificial boost in high frequency response so that PM and FM sound the same at the receiver. A pre-emphasis network tailors the frequency response in the FM transmitter. De-emphasis is employed in the receiver to restore a flat audio response.
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The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to "reinsert the carrier" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be "IF-derived", some say "RF-Derived" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or "AF-derived" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be "IF-derived", some say "RF-Derived" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or "AF-derived" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be "IF-derived", some say "RF-Derived" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or "AF-derived" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be "IF-derived", some say "RF-Derived" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or "AF-derived" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The AGC threshold is the level in the monitored circuit at which the AGC circuit begins to reduce gain. The AGC decay time determines how quickly gain is restored once the strong signal disappears.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to "reinsert the carrier" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The Image is the other frequency that can successfully mix with the Local Oscillator and produce an output out of the Mixer at the Intermediate frequency. Selectivity ahead of the Mixer must be employed to prevent that signal from reaching the Mixer.
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Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Whether injection from the Local Oscillator is above or below the operating frequency, the Image Frequency is always separated from the operating frequency by twice the Intermediate Frequency. A very high Intermediate Frequency moves the Image well out of the preselector bandpass.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses.
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Key words: NOT A DIRECT CAUSE. Temperature variations, voltage variations and movements due to mechanical stresses will cause changes in frequency. The selection of feedback components, notably their temperature coefficient, is paramount for stability. Dial accuracy is not instability per se.
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Stability is the ability to stay on frequency despite other variations. The Local Oscillator indirectly sets the operating frequency. Temperature variations, voltage variations and movements due to mechanical stresses will cause changes in frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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"The FM Two-tone, third-order dynamic range, 10-MHz offset ... is a wide-band dynamic-range test on VHF equipment, using two strong signals just outside the amateur band (usually the abode of nearby pager transmitters). (...) This test is a good indicator of relative IMD performance". (RFI - Intermodulation, ARRL, Ed Hare, W1RFI)
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