or
General Class (Until Jul 1, 2023)
Subelement G8
Signals and Emissions
Section G8B
Frequency mixing; multiplication; bandwidths of various modes; deviation; duty cycle; intermodulation
Which mixer input is varied or tuned to convert signals of different frequencies to an intermediate frequency (IF)?
• Image frequency
Local oscillator
• RF input
• Beat frequency oscillator

In the front end of a receiver, the incoming signal is at a fixed frequency. The only thing we have control over is the LO frequency. As this local oscillator is varied, a different incoming RF signal is mixed with it and presented to the IF. This facilitates "tuning" the radio to different RF frequencies.

Last edited by edponce@yahoo.com. Register to edit

Tags: arrl chapter 5 arrl module 20

If a receiver mixes a 13.800 MHz VFO with a 14.255 MHz received signal to produce a 455 kHz intermediate frequency (IF) signal, what type of interference will a 13.345 MHz signal produce in the receiver?
Image response
• Mixer interference
• Intermediate interference

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.

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"

Last edited by stukaju87g. Register to edit

Tags: arrl chapter 5 arrl module 20

What is another term for the mixing of two RF signals?
Heterodyning
• Synthesizing
• Cancellation
• Phase inverting

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.

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

Last edited by katzelover. Register to edit

Tags: arrl chapter 5 arrl module 18

What is the stage in a VHF FM transmitter that generates a harmonic of a lower frequency signal to reach the desired operating frequency?
• Mixer
• Reactance modulator
• Pre-emphasis network
Multiplier

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.

Last edited by gconklin. Register to edit

Tags: arrl chapter 5 arrl module 18

What is the approximate bandwidth of a PACTOR-III signal at maximum data rate?
• 31.5 Hz
• 500 Hz
• 1800 Hz
2300 Hz

PACTOR-III's maximum uncompressed speed is 2722 bps. Using online compression, up to 5.2 kbps is achievable. This requires an audio passband from 400 Hz to 2600 Hz (for PACTOR-III speedlevel 6). The occupied bandwidth at the --40 dB points is 2.4 kHz (from 300 Hz to 2700 Hz).

Also if helpful think PACTOR 3 --> 2(3)00 Hz

or

PACTOR has 2 syllables, PACTOR 3 --> 2300 Hz

Last edited by br brendan. Register to edit

Tags: arrl chapter 6 arrl module 25

What is the total bandwidth of an FM phone transmission having 5 kHz deviation and 3 kHz modulating frequency?
• 3 kHz
• 5 kHz
• 8 kHz
16 kHz

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

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:

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

Wikipedia ► Carson bandwidth rule

Last edited by doc.simonson. Register to edit

Tags: arrl chapter 5 arrl module 19

What is the frequency deviation for a 12.21 MHz reactance modulated oscillator in a 5 kHz deviation, 146.52 MHz FM phone transmitter?
• 101.75 Hz
416.7 Hz
• 5 kHz
• 60 kHz

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

Last edited by dogshed. Register to edit

Tags: arrl chapter 5 arrl module 19

Why is it important to know the duty cycle of the mode you are using when transmitting?
• To aid in tuning your transmitter
Some modes have high duty cycles that could exceed the transmitter's average power rating
• To allow time for the other station to break in during a transmission
• The attenuator will have to be adjusted accordingly

(B). 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.

Last edited by edponce@yahoo.com. Register to edit

Tags: arrl chapter 6 arrl module 25

Why is it good to match receiver bandwidth to the bandwidth of the operating mode?
• It is required by FCC rules
• It minimizes power consumption in the receiver
• It improves impedance matching of the antenna
It results in the best signal-to-noise ratio

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.

Last edited by edponce@yahoo.com. Register to edit

Tags: arrl chapter 5 arrl module 20

What is the relationship between transmitted symbol rate and bandwidth?
• Symbol rate and bandwidth are not related
Higher symbol rates require wider bandwidth
• Lower symbol rates require wider bandwidth
• Bandwidth is always half the symbol rate

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.

Last edited by pjmotor12613. Register to edit

Tags: arrl chapter 6 arrl module 25

What combination of a mixer's Local Oscillator (LO) and RF input frequencies is found in the output?
• The ratio
• The average
The sum and difference
• The arithmetic product

Hint: SUM of both gives you DIFFERENCE ( -10 + 5)

A mixer combines two input frequencies to produce an output signal containing both frequencies. For example, a Local Oscillator signal of frequency A is combined with an RF signal of frequency B. When mixed, the output signal will contain a signal of frequencies (A + B) and abs(A - B).

Mixers have many applications, such as in superheterodyne receivers, which convert very high frequencies down to lower frequencies that are more easily handled by the radio. In that case, where you want a lower frequency, the A+B signal will be filtered out.

Sometimes you may want to produce a signal with a higher frequency; in that case you can use a mixer to generate A+B and A-B signals, and simply filter out the A-B signal.

https://en.m.wikipedia.org/wiki/Frequency_mixer

Last edited by edponce@yahoo.com. Register to edit

Tags: arrl chapter 5 arrl module 18

What process combines two signals in a non-linear circuit or connection to produce unwanted spurious outputs?