Hint: A FILTER - PROCESSES

Modulation is the process that combines the audio signal with the radio frequency. In AM (amplitude modulation) this encodes all of the information about the audio signal in the sidebands, at which point the carrier frequency serves no further purpose.

A balanced modulator first modulates and then also suppresses the now superfluous carrier signal.

The output of the balanced modulator gets passed to the filter, which removes one of the sidebands. That single sideband is then forwarded on to the mixer which will produce a signal with the desired frequency.

For more info see Wikipedia: Single-sideband modulation - 3.1 Bandpass filtering

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A balanced modulator mixes the RF with the carrier, but suppresses the carrier frequency in the output, passing the upper and lower sidebands.

SILLY HINT: Three of the answers have modulate mentioned, but only one has the "balance" of "double-sided"

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One reason to use an impedance matching transformer is to maximize the transfer of power. This type of transformer alters the current and voltages, which changes the impedances between the power source and load. Matching the impedances allows for maximum power transfer, so this is one component which may be used for the function.

SILLY HINT: The correct choice has PRESENT which is closer in meaning to match, where the incorrect choices all have verbs that mean to make something smaller (minimize and reduce).

SILLY HINT 2 : The correct choice is the only one that includes "impedance"

For more info see Wikipedia: Impedance matching, Impedance Matching Transformer

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A product detector is used in a single sideband (SSB) receiver to extract the modulated signal. When receiving a single sideband signal, the product detector combines the received signal with a local oscillator signal. By multiplying or mixing these signals, the product detector creates a new signal that contains the original voice or information.

This demodulated signal can then be further processed and converted into audio or data that we can perceive or interpret. In essence, the product detector plays a vital role in separating the modulated signal from the carrier wave, allowing us to retrieve and use the transmitted communication.

SILLY HINT: The "product" we are detecting is the desired signal (audio) - and it has to be extracted to be useful.

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Variable frequency with the stability of a crystal oscillator is an advantage of a transceiver controlled by a direct digital synthesizer (DDS). The DDS can be used over a wide range of frequencies and can be precisely controlled to create finely stepped sine wave forms while producing very little phase noise.

For more info see Wikipedia: Direct digital synthesizer

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Silly Hint: A synthesizer in a music instrument creates variable frequencies

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An advantage of a receiver digital signal processor (DSP) IF (intermediate frequency) filter compared to an analog filter, is that a wide range of filter bandwidths and shapes can be created. The software and processing abilities of the DSP unit make it a very flexible instrument for either filtering or other modifications, signal modulation or other adjustments to the received signal.

For more info see Wikipedia: Digital signal processor, Digital Signal Processing

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Hint: To be “inside” is to “insert”

A filter's pass band is the band that allows the signal to pass through it. However, even in the pass band the filter does attenuate the signal some. This base level of attenuation from having the filter inserted into the signal path is called the "Insertion loss".

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SILLY HINT: To "receive" something (receiver) means for something to "come in". There are two answers that start with "Input" therefore there is more than one answer that starts with "input," so only correct answer must be "D"-All these choices correct.

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I & Q signals are used as components of a quadrature signal. By definition, they are separated by 90 degrees (a right angle). You just need to memorize this. It may help to remember they are QUADrature, think of dividing a signal into 4 parts: 360 degrees divided by 4 is 90 degrees.

Silly memory hint: The "average" IQ of a human is generally standardized to be around 100 on most tests, which is closest to 90 of the available options. 180 would be way too high, 45 too low, and 0 is impossible.

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I and Q signals are the In-phase and Quadrature components of a signal. They provide enough data for software to be able to decode many different types of modulation.

It is debatable whether "all types" of modulation can be created, but certainly a great many different types can be. That is the power of a Software Defined Radio!

Addressing the distractors:

• The need for high resolution analog-to-digital converters is eliminated - No, actually the higher the resolution on the A2D converters the more you can do with the SDR as those are what allow converting the provided signals (analog) into a digital form!

• Minimum detectable signal level is reduced - No, there isn't any real impact on that, though it's conceivable that you may be able to make better use of what you have with good enough software.

• Converting the signal from digital to analog creates mixing products - No, there is no reason that D2A converters should create mixing products.

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Memory hints:

• A person with high IQ can create ALL kinds of things

• Software requires processing

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The transmitter of the software-defined radio (SDR) is just a "transmitter", so it can't do anything since it just sends and receives signal to and from the air and doesn't try to encode or decode them but just process them directly to the computer.

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A low pass filter passes the low frequencies and rejects the high frequencies. "Cutoff" indicates the point at which frequencies are rejected.

Note that "roll off" describes the shape of the filter's curve between the pass band and stop band. It isn't a specific frequency, it is more likely to be described as a rate of change like dB/decade.

Hint: A quarterback also throws a “Lowpass” to “cut-off” any sacks

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Notch depth describes the ability to accept a signal in the center of a band pass filter.

Rolloff describes the steepness of the edge of a filter between the pass band and stop band.

Insertion loss describes the loss across the band by the insertion of the filter into the circuit.

Ultimate rejection describes the ability to reject signals outside the pass band.

Mnemonics:

• A maximum reject is an ultimate reject.
• The question and answer both have reject.
• Ultimate means "as far as possible", the filter rejects signals far from its "passband".

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Hint: a bandwidth has UPPER and LOWER limits

"Upper and lower half-power" is correct. These might also be referred to as the upper and lower cutoff or -3dB frequencies.

Don't be tricked by: "Cutoff and Rolloff". Rolloff describes the shape of the edge of the filter's transfer function, not a specific frequency.

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Half-Power Point, aka Half-Power Frequencies

The half-power point is the point at which the output power has dropped to half of its peak value; that is, at a level of approximately -3 dB.

In filters, optical filters, and electronic amplifiers, the half-power point is also known as half-power bandwidth and is a commonly used definition for the cutoff frequency.

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