(A). The mixer is the receiver stage which would combine a 14.250 MHz input signal with a 13.795 MHz oscillator signal to produce a 455 kHz intermediate frequency (IF) signal.

For single sideband transmissions a mixer is used to combine the two input signals (14.250 MHZ, and 13.795) to produce a new carrier signal which is an intermediate median frequency. Along with this new IF signal, two side signals are produced, the first being the sum of the two input frequencies, which becomes the upper sideband frequency (28.045 MHz), and the second being the difference between the input frequencies which becomes the lower sideband frequency (0.455 MHz = 455 kHz). Filters, etc are then used to suppress the undesired portions of the signal and allow the desired sideband (455 kHz) to pass for SSB transmittion.

For more info see Wikipedia: Single-sideband modulation, Frequency Mixer

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Image response would be the type of interference produced. The mixer produces intermediate frequencies based on the sum (USB) and the difference (LSB) between the two input frequencies.

The difference between the 14.255 MHz and 13.800 MHz signals would produce an LSB intermediate frequency of 0.455 MHz = 455 kHz. However, when the 13.345 MHz signal is encountered, the difference between 13.800 MHz and 13.345 MHz is ALSO 0.455 MHz = 455 kHz.

When the interference is produced at the same frequency as the desired frequency, this is called image response interference. The remedy is to use input filtration prior to the mixing stage.

For more info see Wikipedia: image response interference

Silly Hint: With all the math, this question is an ugly image of a question, so it makes you think of an ugly "Image response"

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Heterodyning is the term listed which refers to the mixing of two RF signals. The heterodyning system uses a local HF oscillator, a mixer, and detector to modulate the carrier signal producing upper and lower sidebands.

For more info see Wikipedia: heterodyning

Hint: Hetero means different or other like 2 different signals.

Memory aid: When you are dining (dyning) somewhere there may be a mix of foods.

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Hint: A harmonic has MULTIPLE sounds

The frequency multiplier is the stage in a VHF FM transmitter that generates a harmonic of a lower frequency signal to reach the desired operating frequency. The frequency multiplier produces signals at harmonic multiples (double, triple, etc) of the modulated signal to bring the frequency to the desired output level.

For more info see Wikipedia: Frequency multiplier

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(C). Frequency modulated (FM) phone signals are not used below 29.5 MHz because the wide bandwidth is prohibited by FCC rules.

The HF frequency bands are narrow ranges. The FCC restricts frequencies at 29.5 MHz and below to bandwidth usage of less than 16 kHz. FM phone signals use a bandwidth of about 16 kHz, and so are too large. These bands primarily use single sideband phone transmissions to reduce bandwidth to allowable ranges.

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\[(f_{\text{dev}} + f_{\text{mod}}) \times 2 = \text{FM Bandwidth}\]

To calculate the total bandwidth of an FM phone transmission, use Carson's bandwidth rule by adding together the frequency deviation and the modulating frequency then multiplying the sum by \(2\):

\[BW = (f_{\text{dev}} + f_{\text{mod}}) \times 2\]

Where:

• \(BW\) is the total FM phone bandwidth
• \(f_{\text{dev}}\) is the frequency deviation
• \(f_{\text{mod}}\) is the modulating frequency

So for this question:

\[f_{\text{dev}} = 5 \text{kHz}\] \[f_{\text{mod}} = 3 \text{kHz}\]

Therefore:

\[BW = (5 \text{kHz} + 3 \text{kHz}) \times 2\] \[BW = 8 \text{kHz} \times 2\] \[BW = 16 \text{kHz}\]

Memory aid: \(5 \times 3 = 15\) and 16 is the closest

Wikipedia ► Carson bandwidth rule

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416.7 Hz is the frequency deviation for a 12.21 MHz reactance modulated oscillator in a 5-kHz deviation, 146.52 MHz FM phone transmitter.

To calculate the frequency deviation, first calculate the multiplication factor of the FM transmitter:

\begin{align} \small \text{Multiplication Factor} &= \small { \frac{\text{Transmitter Frequency}}{\text{HF Oscillator Frequency}}}\\ &= \frac{146.52\ \text{MHz}}{12.21\ \text{MHz}}\\ &= 12 \end{align}

Next, divide the transmitter deviation by the multiplication factor:

\begin{align} \small \text{Frequency deviation} &= \small{ \frac{\text{Transmitter Deviation}}{\text{Multiplication Factor}}}\\ &= \frac{ 5\ \text{kHz}}{12}\\ &= \frac{ 5000\ \text{Hz}}{12}\\ &= 416.7\ \text{Hz} \end{align}

Silly Hint: 146 think 416, and 146.52, so 5 + 2 = 7, and 416.7.

Alt: The standard FM deviation allowed is 5 KHz so, 5 ÷ 12 = 0.416 KHz, or 416 Hz

Alt: 5/150 simplifies to 1/30. 1/30th of 12 is 0.4

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It is important to know the duty cycle of the data mode you are using when transmitting because some modes have high duty cycles which could exceed the transmitter's average power rating.

Data modes vary in the percentage of time that they are actually transmitting at full power versus the amount of "off time" between signals. This is referred to as the duty cycle. As an example, the intermittant dots and dashes of CW mean that the transmitter is actually only operating at full power for somewhere around 40 to 50% of the time. Some of the RTTY data modes on the other hand, can actually run at full power for close to 100% of the transmission time. Because these modes have such high duty cycles, it may be necessary to reduce the power used so that the transmitter's average power rating is not exceeded.

SILLY HINT: Do your "duty" "duty"

For more info see Wikipedia: Duty cycle

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Matching bandwidths reduces the amount of noise outside the desired frequency range.

Doing so means less energy is lost in filtering, resulting in a better signal-to-noise ratio.

For more info see Wikipedia: Signal-to-noise ratio

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Hint: “S” = symbol Phase Shift Keying @31 Baud (symbol rate)

(A). The number 31 in the abbreviation for PSK31 is the approximate transmitted symbol rate.

PSK31 is a type of data mode of "Phase Shift Keying" at "31 baud." The actual baud rate used is 31.25 Hz. Similarly, the less common PSK10 and PSK 05 would correspond to baud rates of approximately 10 baud and 5 baud respectively.

For more info see Wikipedia: PSK31

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Hint: FEC forwards (TRANSMITS) redundant data

(C). Forward error correction allows the receiver to correct errors in received data packets by transmiting redundant information with the data.

This type of correction used in packet data transmissions is useful especially over "noisy" bands or in case of interference which may corrupt the signal.

For more info see Wikipedia: Forward error correction (FEC)

Hint: Look for the word “Data” in the answer.

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The relationship between transmitted symbol rate and bandwidth is that higher symbol rates require higher amounts of bandwidth.

As the symbol rate for a data transmisson increases (baud rate), the amount of bandwidth required to send that signal must also increase in order to maintain a low signal-to-noise ratio.

Hint: More information requires more space.

For more info see Wikipedia: Symbol rate

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