2019 No Nonsense General Class Study Guide: Amateur Radio Practices, part II

Interference with consumer electronics, grounding, DSP

At some point or another, your amateur radio station will interfere with a radio or television set, a PA system, or a telephone. A SSB transmission generally causes some kind of humming, while a CW transmission can cause humming or clicking. Sometimes this may be your fault, other times it may be the fault of the device. In either case, you should do everything you can to eliminate this interference.

QUESTION: What sound is heard from an audio device or telephone if there is interference from a nearby single sideband phone transmitter? (G4C03)
ANSWER: Distorted speech

QUESTION: What is the effect on an audio device when there is interference from a nearby CW transmitter? (G4C04)
ANSWER: On-and-off humming or clicking

Fortunately, there are many things you can do to reduce or eliminate the interference. For example, you might connect a bypass capacitor across speaker leads to reduce interference to an audio device. To reduce RF picked up by audio cables, you might use a snap-on ferrite choke. I often advise amateurs to have a handful of these on hand for this type of application.

QUESTION: Which of the following might be useful in reducing RF interference to audio frequency devices? (G4C01)
ANSWER: Bypass capacitor

QUESTION: Which of the following would reduce RF interference caused by common-mode current on an audio cable? (G4C08)
ANSWER: Placing a ferrite choke around the cable

 

Proper grounding is also important to reduce interference. Rather than connecting the grounds in a daisy-chain fashion, you should connect them all to a single point. This will help you avoid ground loops, which can cause a hum on your phone signal.

QUESTION: How can a ground loop be avoided? (G4C09)
ANSWER: Connect all ground conductors to a single point

QUESTION: What could be a symptom of a ground loop somewhere in your station? (G4C10)
ANSWER: You receive reports of “hum” on your station’s transmitted signal

When grounding RF equipment, keep ground cables short and direct to prevent high-impedance or resonant ground connections. A long ground wire may present a high impedance at HF frequencies and instead of grounding station equipment enclosures may cause high voltages to be present. This, in turn, may cause operators to receive an RF burn when touching the enclosure. Also be sure to “bond” the enclosures together to prevent any potential differences that can cause hazard voltages, or “hot spots,” between the enclosures.

QUESTION: What effect can be caused by a resonant ground connection? (G4C06)
ANSWER: High RF voltages on the enclosures of station equipment.

QUESTION: What might be the problem if you receive an RF burn when touching your equipment while transmitting on an HF band, assuming the equipment is connected to a ground rod? (G4C05)
ANSWER: The ground wire has high impedance on that frequency

QUESTION: Why must the metal enclosure of every item of station equipment be grounded? (G4C13)
ANSWER: It ensures that hazardous voltages cannot appear on the chassis

QUESTION: What technique helps to minimize RF “hot spots” in an amateur station? (G4C11)
ANSWER: Bonding all equipment enclosures together

 

A common complaint of amateur radio operators is electrical noise that seems to be on every band. This may be caused by arcing in a power line transformer or at some other connection.

QUESTION: Which of the following could be a cause of interference covering a wide range of frequencies? (G4C02)
ANSWER: Arcing at a poor electrical connection

One way to eliminate noise is to use digital signal processor, or DSP. Modern amateur radio transceivers have built-in DSPs that operate at IF frequencies. DSP filters generally work better than analog filters.

QUESTION: Which of the following is an advantage of a receiver DSP IF filter as compared to an analog filter? (G4C12)
ANSWER: A wide range of filter bandwidths and shapes can be created

 

Speech processors, S meters, sideband operation near band edges

Speech processors can be very useful when operating SSB. Speech processors increase the average power output of an SSB transmitter, thereby increasing the intelligibility of the signal when conditions are poor.

QUESTION: What is the purpose of a speech processor as used in a modern transceiver? (G4D01)
ANSWER: Increase the intelligibility of transmitted phone signals during poor conditions

QUESTION: Which of the following describes how a speech processor affects a transmitted single sideband phone signal? (G4D02)
ANSWER: It increases average power

Of course, you must adjust it properly to gain these benefits. An incorrectly adjusted speech processor can cause more problems than it solves.

QUESTION: Which of the following can be the result of an incorrectly adjusted speech processor?(G4D03)
ANSWER: All of these choices are correct
• Distorted speech
• Splatter
• Excessive background pickup

 

Most commercial receivers have an S meter that indicates received signal strength. The S meter uses a logarithmic scale, with an increase of one S unit being equivalent to a gain of 6 dB. What that means is that a signal whose S meter reading is one unit higher than another is four times as strong as the other signal.

QUESTION: Where is an S meter found? (G4D06)
ANSWER: In a receiver

QUESTION: What does an S meter measure? (G4D04)
ANSWER: Received signal strength

QUESTION: How much must the power output of a transmitter be raised to change the S meter reading on a distant receiver from S8 to S9? (G4D07)
ANSWER: Approximately 4 times

QUESTION: How does a signal that reads 20 dB over S9 compare to one that reads S9 on a receiver, assuming a properly calibrated S meter? (G4D05)
ANSWER: It is 100 times stronger

 

When operating near band edges, it’s important to know the frequency range that your signal will actually occupy so that your transmissions stay within the amateur band. When operating lower sideband, or LSB, your signal actually occupies a 3 kHz space below the displayed carrier frequency, so you don’t want to set your transceiver to a frequency less than 3 kHz above the band edge when operating LSB. So, for example, the lowest frequency on which a General Class operator can operate phone is 7.175 MHz, so you should not set your radio to a frequency less than 7.178 MHz to make sure that your transmitted signal stays within the General Class portion of the band.

QUESTION: How close to the lower edge of the phone segment should your displayed carrier frequency be when using 3 kHz wide LSB? (G4D10)
ANSWER: At least 3 kHz above the edge of the segment

QUESTION: What frequency range is occupied by a 3 kHz LSB signal when the displayed carrier frequency is set to 7.178 MHz? (G4D08)
ANSWER: 7.175 to 7.178 MHz

Similarly, when operating USB, your signal occupies a space starting at the displayed carrier frequency and extending up 3 kHz. So, to stay within your assigned band, you should not set your transceiver to a frequency that is higher than 3 kHz below the upper band edge.

QUESTION: How close to the upper edge of the phone segment should your displayed carrier frequency be when using 3 kHz wide USB? (G4D11)
ANSWER: At least 3 kHz below the edge of the band

QUESTION: What frequency range is occupied by a 3 kHz USB signal with the displayed carrier frequency set to 14.347 MHz? (G4D09)
ANSWER: 14.347 to 14.350 MHz

 

HF mobile radio installations; emergency and battery powered operation

Operating mobile, that is from a car or boat, is an activity enjoyed by many radio amateurs. Amateurs can do almost everything from a mobile station that they can do at a fixed station.
When setting up a mobile station, the first thing to consider is how you are going to supply power to your radios. In general, it’s preferable to wire your transceiver directly to the vehicle’s battery with connections as short as possible, using heavy gauge wire.

QUESTION: Which of the following direct, fused power connections would be the best for a 100 watt HF mobile installation? (G4E03)
ANSWER: To the battery using heavy gauge wire

QUESTION: Why is it best NOT to draw the DC power for a 100 watt HF transceiver from a vehicle’s auxiliary power socket? (G4E04)
ANSWER: The socket’s wiring may be inadequate for the current being drawn by the transceiver

 

One common complaint when operating mobile is that the vehicle’s electronics generate noise that interferes with sensitive HF receivers. There are many sources of RF noise in a vehicle.

QUESTION: Which of the following may cause receive interference in a radio installed in a vehicle? (G4E07)
ANSWER: All of these choices are correct
• The battery charging system
• The fuel delivery system
• The vehicle control computer

 

As you can imagine, mobile antennas for HF operation are always a compromise because they are so short with respect to wavelength. The reason for this is that mobile HF antennas are much shorter than full-size antennas.

QUESTION: Which of the following most limits an HF mobile installation? (G4E05)
ANSWER: The antenna system

QUESTION: What is one disadvantage of using a shortened mobile antenna as opposed to a full-size antenna? (G4E06)
ANSWER: Operating bandwidth may be very limited

One way to make a physically short antenna resonate on HF is to use a capacitance hat. Like a loading coil, a capacitance hat makes an antenna seem electrically longer than it really is. Because mobile antennas are so short, the voltage at the tip of the antenna may be very high. To reduce the possibility of a high-voltage discharge, some mobile antennas have a corona ball. This ball disperses the charge at the tip of an antenna, thereby decreasing the voltage.

QUESTION: What is the purpose of a capacitance hat on a mobile antenna? (G4E01)
ANSWER: To electrically lengthen a physically short antenna

QUESTION: What is the purpose of a corona ball on an HF mobile antenna? (G4E02)
ANSWER: To reduce RF voltage discharge from the tip of the antenna while transmitting

 

Some amateurs use solar cells to power their equipment while operating mobile or portable. Solar cells take advantage of a process called photovoltaic conversion to convert the power of the sun into electrical power.

QUESTION: What is the name of the process by which sunlight is changed directly into electricity? (G4E08)
ANSWER: Photovoltaic conversion
QUESTION: What is the approximate open-circuit voltage from a fully illuminated silicon photovoltaic cell? (G4E09)
ANSWER: 0.5 VDC

Some amateurs use photovoltaic cells to recharge storage batteries. These systems often have a series diode connected between a solar panel and the battery to prevent the battery from discharging through the solar panel when the sun isn’t shining.

QUESTION: What is the reason that a series diode is connected between a solar panel and a storage battery that is being charged by the panel? (G4E10)
ANSWER: The diode prevents self discharge of the battery though the panel during times of low or no illumination

Some amateurs even use wind power as a power source. Like other power sources, wind has advantages and disadvantages.

QUESTION: Which of the following is a disadvantage of using wind as the primary source of power for an emergency station? (G4E10)
ANSWER: A large energy storage system is needed to supply power when the wind is not blowing