Correct answer: an interrupted carrier

Morse code is transmitted using continuous wave (CW) transmission by switching the transmitter carrier on and off in accordance with the dots and dashes of the code.

This produces a radio-frequency carrier that is present during key-down and absent during key-up.

• A voice modulated carrier is used for speech transmission (e.g. AM or SSB).
• A continuous carrier with no interruption would convey no information.
• A series of clicks does not describe the RF transmission method.

Therefore, Morse code is usually transmitted as an interrupted carrier.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: powered from a regulated DC supply

A VFO (Variable Frequency Oscillator) must operate under stable conditions to maintain a constant output frequency.

Variations in supply voltage can cause changes in the oscillator’s operating point, leading to frequency drift.

Using a regulated DC supply helps maintain a constant voltage and improves frequency stability.

• A non-regulated AC supply would introduce voltage variations.
• A plastic box does not provide electrical stability.
• Frequency change with temperature would reduce stability.

Therefore, the VFO should be powered from a regulated DC supply for high frequency stability.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: occupy about half the bandwidth of AM transmissions

Single Sideband (SSB) transmission uses only one sideband and suppresses the carrier.

In conventional AM:

• carrier + upper sideband + lower sideband are transmitted

So the bandwidth is:

\[ B_{\text{AM}} = 2 f_m \]

In SSB:

• only one sideband is transmitted

\[ B_{\text{SSB}} = f_m \]

Thus:

\[ B_{\text{SSB}} = \frac{1}{2} B_{\text{AM}} \]

• SSB does not occupy twice the bandwidth.
• It does not inherently contain more information.
• It is not directly compatible with FM.

Therefore, SSB transmissions occupy about half the bandwidth of AM transmissions.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: suppress the carrier while producing two sidebands

A balanced modulator combines the audio signal with the RF carrier in a way that cancels the carrier component at its output while still producing both the upper and lower sidebands. The result is a double sideband suppressed carrier (DSB-SC) signal.

This is the required first step in generating an SSB signal. A filter or phasing network later removes one of the sidebands.

• make sure that the carrier and both sidebands are in phase is incorrect, the carrier is intentionally suppressed, not phase aligned.
• make sure that the carrier and both sidebands are 180 degrees out of phase is incorrect and does not describe the function of a balanced modulator.
• ensure that the percentage of modulation is kept constant relates to modulation control or ALC, not carrier suppression.

Therefore, the purpose of a balanced modulator is to suppress the carrier while producing two sidebands.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: A — the transmitter modulation deviation is too high

In FM (frequency modulation), the audio signal causes the carrier to deviate above and below its centre frequency. The maximum permitted deviation for narrow-band FM in the 2 m amateur band is typically ±5 kHz. If the deviation is set too high — often caused by the microphone gain or audio drive level being too high — the signal occupies excessive bandwidth and adjacent receivers cannot decode it cleanly, producing distortion (sometimes called "over-deviation" or "splatter"). Other stations hear the transmission as harsh or unintelligible.

• B — antenna too low: A low antenna reduces signal strength and may cause multipath issues, but it does not directly cause audio distortion at the receiving end.
• C — transmitter has become unsynchronised: FM simplex transmitters do not use a synchronisation process; this is not a meaningful failure mode for an FM voice transmitter.
• D — transmitter frequency split is incorrect: A frequency split (offset) is used for repeater operation, not simplex. On simplex both transmit and receive frequencies are the same, so a split setting is irrelevant.

Therefore, distorted FM audio reported by multiple stations is a classic symptom of excessive modulation deviation, and the cure is to reduce the microphone gain or audio drive level on the transmitter.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: before the power amplifier

In a transmitter, the driver stage provides sufficient signal power to properly drive the final power amplifier stage.

The typical signal chain is:

Oscillator → Buffer → Driver → Power Amplifier → Output Filter → Antenna

• The driver is not placed between the oscillator and buffer.
• It is not necessarily combined with a frequency multiplier.
• The output low-pass filter is located after the power amplifier.

Therefore, the driver stage is located before the power amplifier.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: D — increase the power fed to the antenna

The final amplifier (also called the power amplifier or PA) is the last active stage in a transmitter chain. Its role is to boost the RF signal to a level sufficient to drive the antenna with the desired transmit power. All earlier stages operate at relatively low power levels; the final amplifier raises that power to the rated output of the transmitter.

• A — increase the frequency of a signal: Frequency multiplication is performed by dedicated multiplier stages earlier in the transmitter chain, not by the final amplifier.
• B — isolate the multiplier and later stages: Isolation between stages is the function of buffer amplifiers, which are inserted between oscillator or multiplier stages to prevent unwanted coupling.
• C — produce a stable radio frequency: A stable RF signal is generated by the master oscillator (often crystal-controlled) at the front end of the transmitter, not by the final amplifier.

Therefore, the final amplifier's sole purpose is to increase the RF power delivered to the antenna to the required transmit level.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: is dissipated as heat

An RF power amplifier converts DC input power into RF output power, but this process is not 100% efficient.

The difference between the DC input power and the RF output power is the power lost due to inefficiencies in the amplifier, such as:

• internal resistance
• switching losses
• non-linear operation

This lost power is converted into heat within the amplifier components.

• It does not radiate from the antenna.
• Feedline loss occurs after the amplifier.
• Oscillating current is part of normal RF operation.

Therefore, the difference is dissipated as heat.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: information to be impressed on to a carrier

Modulation is the process of combining an information signal (such as voice or data) with a high-frequency carrier wave.

This allows the information to be transmitted efficiently over long distances.

• Removing information from a carrier is demodulation.
• Combining voice and Morse is not the purpose of modulation.

Therefore, modulation allows information to be impressed on to a carrier.

Last edited by jim.carroll. Register to edit

Tags: none

Correct answer: C — peak envelope power

For a Single Sideband (SSB) transmitter, the standard way to rate the output power of a linear amplifier is Peak Envelope Power (PEP). SSB signals have no constant carrier — the instantaneous power varies with the voice modulation. PEP is measured at the peak of the RF envelope, representing the highest power the amplifier must deliver during a modulation peak. This is the most meaningful rating for a linear amplifier handling SSB, as it defines the headroom required to avoid distortion on speech peaks.

\[ P_{PEP} = \frac{V_{peak}^2}{2R} \]

where \(V_{peak}\) is the peak envelope voltage and \(R\) is the load impedance.

• A. Peak DC input power — Input power (DC supply voltage × current) describes the power drawn from the supply, not the RF output power. It does not directly specify amplifier output capability for SSB.
• B. Mean AC input power — Average (mean) power is appropriate for continuous carriers (e.g. AM or FM), but SSB power varies continuously with speech, making the mean a poor indicator of the amplifier's required output rating.
• D. Unmodulated carrier power — SSB suppresses the carrier entirely; there is no unmodulated carrier to measure. This metric is irrelevant to SSB transmitters.

Therefore, the output power of a linear amplifier in an SSB transmitter is correctly specified by the peak envelope power (PEP), which captures the maximum instantaneous RF output at modulation peaks.

Last edited by jim.carroll. Register to edit

Tags: none