2014 Tech study guide: public service and emergency operations

There were quite a few changes to this section. Questions were added about net operations, and the question about charging a battery connecting it in parallel with a vehicle battery was moved here…Dan

One of the reasons amateur radio exists at all is that ham radio operators are uniquely set up to provide emergency and public-service communications. As a result, many hams consider it an obligation to be prepared to help out when called upon to do so. This includes having the proper equipment and knowing the proper operating procedures.

There are two organizations that provide emergency communications: the Radio Amateur Civil Emergency Service (RACES) and the Amateur Radio Emergency Service (ARES). The thing that both RACES and ARES have in common is that both organizations may provide communications during emergencies. (T2C04) The Amateur Radio Emergency Service (ARES) is a group of licensed amateurs who have voluntarily registered their qualifications and equipment for communications duty in the public service. (T2C12) All of these choices are correct when describing the Radio Amateur Civil Emergency Service (RACES) (T2C05):

  • A radio service using amateur frequencies for emergency management or civil defense communications
  • A radio service using amateur stations for emergency management or civil defense communications
  • An emergency service using amateur operators certified by a civil defense organization as being enrolled in that organization

When an emergency occurs, it’s common for amateur radio operators to form a network or “net” to facilitate emergency communications. The net is led by the net control station, whose job it is to make sure that messages are passed in an efficient and timely manner.

Stations other than the net control station are said to “check into” the net. An accepted practice for an amateur operator who has checked into an emergency traffic net is to remain on frequency without transmitting until asked to do so by the net control station. (T2C07) There are, however, times when a station may need to get the immediate attention of the net control station. If this is the case, an accepted practice to get the immediate attention of a net control station when reporting an emergency is to begin your transmission by saying “Priority” or “Emergency” followed by your call sign. (T2C06)

The term for messages passed between stations in an emergency net is “traffic,” and the process of passing messages to and from amateur radio stations is called “handling traffic.” Message traffic may be formal or informal. A characteristic of good emergency traffic handling is passing messages exactly as received. (T2C08) To insure that voice message traffic containing proper names and unusual words are copied correctly by the receiving station, such words and terms should be spelled out using a standard phonetic alphabet. (T2C03)

Formal traffic messages consists of four parts: preamble, address, text, signature. The preamble in a formal traffic message is the information needed to track the message as it passes through the amateur radio traffic handling system. (T2C10) Part of the preamble is the check. The check is a count of the number of words or word equivalents in the text portion of the message. (T2C11) The address is the name and address of the intended recipient, the text is the message itself, and the signature is the part of the message that identifies the originator of the message.

An important thing to remember is that FCC rules always apply to the operation of an amateur station. (T2C01) Amateur station control operators are permitted to operate outside the frequency privileges of their license class only if necessary in situations involving the immediate safety of human life or protection of property. (T2C09)

In an emergency situation, amateur radio operators often find themselves using battery power. It is, therefore, important to keep batteries charged and ready to go. One way to recharge a 12-volt lead-acid station battery if the commercial power is out is to connect the battery in parallel with a vehicle’s battery and run the engine. (T2C02)

2014 Tech study guide: operating procedures

I’m going to lump several sections into this one post. Several questions were added and several updated, but nothing really major was changed….Dan

FM Operation 

Once they get their licenses, most Technicians purchase a VHF/UHF FM transceiver. This type of radio allows them to use repeaters and participate in public-service events.

To use repeaters, you need to know how to set up your radio. Repeaters receive on one frequency and transmit on another. You program your radio so that it receives on the repeater’s transmit frequency and transmits on the repeater’s receive frequency.

The difference between the transmit frequency and receive frequency is called the repeater frequency offset. Plus or minus 600 kHz is the most common repeater frequency offset in the 2 meter band. (T2A01) Plus or minus 5 MHz is a common repeater frequency offset in the 70 cm band. (T2A03)

Repeater operation is called duplex operation because you’re transmitting and receiving on two different frequencies. When the stations can communicate directly without using a repeater, you should consider communicating via simplex rather than a repeater. (T2B12) Simplex communication is the term used to describe an amateur station that is transmitting and receiving on the same frequency. (T2B01)

To help amateurs operating simplex finding one another, frequencies on each band have been set aside as “national calling frequencies.” 446.000 MHz is the national calling frequency for FM simplex operations in the 70 cm band. (T2A02) 146.52 MHz is the national calling frequency for FM simplex operation in the 2 m band.

Because repeaters often operate in environments where there is a lot of interference they are programmed not to operate unless the station they are receiving is also transmitting a sub- audible tone of a specific frequency. These tones are sometimes called PL (short for “private line”) tones or CTCSS tones. CTCSS is the term used to describe the use of a sub-audible tone transmitted with normal voice audio to open the squelch of a receiver. (T2B02) If your radio has not been programmed to transmit the proper sub-audible tone when you transmit, the repeater will not repeat your transmission.

All of these choices are correct when talking about common problems that might cause you to be able to hear but not access a repeater even when transmitting with the proper offset: (T2B04)

• The repeater receiver requires audio tone burst for access
• The repeater receiver requires a CTCSS tone for  access
• The repeater receiver may require a DCS tone sequence for access

One of the controls on a VHF/UHF transceiver is the squelch control. Carrier squelch is the term that describes the muting of receiver audio controlled solely by the presence or absence of an RF signal. (T2B03) You can set this control so that you only get an audio output when receiving a signal.

Microphone gain is also an important control. The reason for this is that the amplitude of the modulating signal determines the amount of deviation of an FM signal. (T2B05) When the deviation of an FM transmitter is increased, its signal occupies more bandwidth. (T2B06) One thing that could cause your FM signal to interfere with stations on nearby frequencies is that you have set your microphone gain too high, causing over-deviation. (T2B07)

In addition to knowing how to set the controls of your radio, you need to know the protocol for making contacts. First, when using a repeater, it is rare to hear stations calling CQ. In place of “CQ,” say your call sign to indicate that you are listening on a repeater. (T2A09) An appropriate way to call another station on a repeater if you know the other station’s call sign is to say the station’s call sign then identify with your call sign. (T2A04)

HF Operation

On the HF bands, when you want to contact another station, you “call CQ.” That is to say, you would say something like, “CQ CQ CQ. This is KB6NU.” The meaning of the procedural signal “CQ” is calling any station. (T2A08) All of these choices are correct when choosing an operating frequency for calling CQ (T2A12):

  • Listen first to be sure that no one else is using the frequency
  • Ask if the frequency is in use
  • Make sure you are in your assigned band

When responding to a call of CQ, you should transmit the other station’s call sign followed by your call sign. (T2A05) For example, if W8JNZ heard my call and wanted to talk to me, he would reply, “KB6NU this is W8JNZ. Over.” Then, I would return the call, and our contact would begin.

It’s important to always identify your station, even when only performing tests. An amateur operator must properly identify the transmitting station when making on-air transmissions to test equipment or antennas. (T2A06) When making a test transmission, station identification is required at least every ten minutes during the test and at the end. (T2A07)

As a technician, you will be able to operate Morse Code on certain portions of the 80 m, 40 m, 15 m, and 10 m bands. To shorten the number of characters sent during a CW contact, amateurs often use three-letter combinations called Q-signals. QRM is the “Q” signal used to indicate that you are receiving interference from other stations. (T2B10) The “Q” signal used to indicate that you are changing frequency is QSY. (T2B11)

General Guidelines

FCC rules specify broadly where amateur radio operators have operating privileges, but are not very detailed. Band plans take this one step further, suggesting where amateurs should use certain modes. While consulting a band plan before operating is a good idea, realize that a band plan is a voluntary guideline for using different modes or activities within an amateur band. (T2A10)

Regarding power levels used in the amateur bands under normal, non-distress circumstances, the FCC rules state that, while not exceeding the maximum power permitted on a given band, use the minimum power necessary to carry out the desired communication. (T2A11) So, while you are authorized to use up to 1,500 W output power on VHF and above (200W on HF), you really should only use that much power when you really need it.

The basics of good operation include keeping your signals clean and avoid interference to other stations. When two stations transmitting on the same frequency interfere with each other, common courtesy should prevail, but no one has absolute right to an amateur frequency. (T2B08)

When identifying your station when using phone, use of a phonetic alphabet is encouraged by the FCC. (T2B09) Most hams around the world understand and use the NATO, or ITU phonetic alphabet. Learn it and use it.

2014 Tech study guide: Basic repair and testing

The addition of T7D12 is the only change to this section…Dan

The most common test instrument in an amateur radio shack is the multimeter. Multimeters combine into a single instrument the functions of a voltmeter, ohmmeter, and ammeter. Voltage and resistance are two measurements commonly made using a multimeter. (T7D07)

You use a voltmeter to measure electric potential or electromotive force. (T7D01) The correct way to connect a voltmeter to a circuit is in parallel with the circuit. (T7D02) When measuring high voltages with a voltmeter, one precaution you should take is to ensure that the voltmeter and leads are rated for use at the voltages to be measured. (T7D12)

An ohmmeter is the instrument used to measure resistance. (T7D05) When measuring circuit resistance with an ohmmeter ensure that the circuit is not powered. (T7D11) Attempting to measure voltage when using the resistance setting might damage a multimeter. (T7D06) What is probably happening when an ohmmeter, connected across a circuit, initially indicates a low resistance and then shows increasing resistance with time is that the circuit contains a large capacitor. (T7D10)

An ammeter is the instrument used to measure electric current. (T7D04) An ammeter is usually connected to a circuit in series with the circuit. (T7D03)

In addition to knowing how to make electrical measurements, knowing how to solder is an essential skill for amateur radio operators. Rosin-core solder is best for radio and electronic use. (T7D08) A grainy or dull surface is the characteristic appearance of a “cold” solder joint. (T7D09)

2014 Tech study guide: RF interference, common transmitter and receiver problems

There were some substantial changes to this section. More questions were added about how to troubleshoot RF interference problems and a couple of questions were eliminated, including one about alternator whine…Dan

Since Murphy’s Law—the law that states if anything can go wrong, it will—applies to amateur radio as much as it does to any other pursuit, at some point you will have to deal with problems. These may include overload, distortion, feedback, and interference.

Let’s first consider interference. All of these choices are correct when talking about causes of radio frequency interference (T7B03):

  • fundamental overload
  • harmonics
  • spurious emissions.

Any of these could cause interference to a TV set or radio, and you will want to take steps to find and eliminate that interference. If someone tells you that your station’s transmissions are interfering with their radio or TV reception, you should first make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel or frequency. (T7B06)

While it’s not very likely that your amateur radio station will interfere with a neighbor’s cable TV service, it can sometimes occur. The first step to resolve cable TV interference from your ham radio transmission is to be sure all TV coaxial connectors are installed properly. (T7B12)

Your amateur radio station may interfere with a nearby radio receiver if your signal is so strong that the receiver cannot reject the signal even though your signal is not on the frequency to which the receiver is tuned. When a receiver is unable to reject strong signals outside the AM or FM band, it can cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally. (T7B02) One way to reduce or eliminate the overloading of a non-amateur radio or TV receiver by an amateur signal is to block the amateur signal with a filter at the antenna input of the affected receiver. (T7B05)

Another device that often experiences interference from amateur radio stations is the telephone. The telephone wires act as antenna and the telephone itself demodulates the signal. One way to reduce or eliminate interference by an amateur transmitter to a nearby telephone is to install an RF filter at the telephone. (T7B04)

All of these choices are correct when considering what may be useful in correcting a radio frequency interference problem (T7B07):

  • Snap-on ferrite chokes
  • Low-pass and high-pass filters
  • Band-reject and band-pass filters

Interference works both ways. Your neighbors may have wireless devices, sometimes called “Part 15 devices,” that can interfere with your station. A Part 15 device is an unlicensed device that may emit low powered radio signals on frequencies used by a licensed service. (T7B09) All of these choices are correct when considering what you should do if something in a neighbor’s home is causing harmful interference to your amateur station (T7B08):

  • Work with your neighbor to identify the offending device
  • Politely inform your neighbor about the rules that require him to stop using the device if
    it causes interference
  • Check your station and make sure it meets the standards of good amateur practice

Perhaps the most common problem that amateur radio operators have is distorted or noisy audio when transmitting. There are many reasons for poor audio. All of these choices are correct if you receive a report that your audio signal through the repeater is distorted or unintelligible (T7B10):

  • Your transmitter may be slightly off frequency
  • Your batteries may be running low
  • You could be in a bad location

Reports of garbled, distorted, or unintelligible transmissions is a symptom of RF feedback in a transmitter or transceiver. (T7B11) Sometimes, garbled or distorted audio when operating FM is the result of over-deviation. Talk farther away from the microphone is one thing you can do if you are told your FM handheld or mobile transceiver is over-deviating. (T7B01)

2014 Tech study guide: receivers, transmitters, and transceivers

This section was changed quite a bit. It used to include four block diagrams, but the question pool committee eliminated all of them. Bravo! Dan

In the early days of radio, amateur radio operators used separate receivers and transmitter units. Nowadays, however, most use radios called transceivers. A  transceiver is a unit combining the functions of a transmitter and a receiver. (T7A02)

There are many different types of transceivers. A multi-mode VHF transceiver is the type of device that is most useful for VHF weak-signal communication. (T7A09) Instead of purchasing a multi-mode VHF transceiver, many amateurs use a transverter to convert the signals from their HF transceiver to the VHF, UHF, and even microwave bands. For example, a device that would take the output of a low-powered 28 MHz SSB exciter and produces a 222 MHz output signal is a transverter. (T7A06)

Many, if not most, new amateurs purchase a handheld transceiver, sometimes called a “handie-talkie,” or HT, as their first transceiver. One disadvantage of of using a handheld transceiver is that the maximum output power is generally only 5 W, and because of this, they have limited range. To increase the low-power output of a handheld transceiver, and therefore its, range, you can use an RF power amplifier. (T7A10)

When talking about a transceivers specifications, we still refer to its receiver and transmitter. The two most important specifications for a receiver are sensitivity and selectivity. Sensitivity is the term that describes the ability of a receiver to detect the presence of a signal. (T7A01) The term that describes the ability of a receiver to discriminate between multiple signals is selectivity. (T7A04)

To improve the sensitivity of a receiver, you can use an RF preamplifier. An RF preamplifier is installed between the antenna and receiver. (T7A11)

Most HF transceivers have some version of a superheterodyne receiver. In a superheterodyne receiver, we first convert an incoming radio signal from its frequency to an intermediate frequency, or IF. The circuit that does this is the mixer. A mixer is used to convert a radio signal from one frequency to another. (T7A03)

When transmitting, we want to generate an RF signal with a specific frequency. To do that, we use an oscillator. Oscillator is the name of a circuit that generates a signal of a desired frequency. (T7A05)

To transmit a voice signal we have to combine an audio frequency signal from the microphone with the RF carrier signal generated by the transmitter. Modulation is the term that describes combining speech with an RF carrier signal. (T7A08) Modulators use a type of mixer circuit to accomplish this process.

2014 Tech study guide: operating controls

Question T4B12 about the function of automatic gain control was added to this section…Dan

To properly operate a transceiver, you need to know how to use the controls. Perhaps the most important transmitter control is microphone gain. If a transmitter is operated with the microphone gain set too high, the output signal might become distorted. (T4B01)

You also need to know how to set the operating frequency of your transceiver. The keypad or VFO knob can be used to enter the operating frequency on a modern transceiver. (T4B02) A way to enable quick access to a favorite frequency on your transceiver is to store the frequency in a memory channel. (T4B04)

A common receiver control on VHF/UHF transceivers is the squelch control. The purpose of the squelch control on a transceiver is to mute receiver output noise when no signal is being received. (T4B03) If set too high, then you will not be able to hear low-level signals.

Another common setting on VHF/UHF transceivers is the offset frequency. This is especially important when operating repeaters. The common meaning of the term “repeater offset” is the difference between the repeater’s transmit and receive frequencies. (T4B11)

A common receiver control on HF transceivers is the RIT control. The term “RIT” means Receiver Incremental Tuning. (T4B07) The receiver RIT or clarifier are controls that could be used if the voice pitch of a single-sideband signal seems too high or low. (T4B06)

Another common control on a receiver is the automatic gain control, or AGC. Its function is to keep received audio relatively constant. (T4B12) This is important because HF signal strengths can vary widely. and that can cause audio levels to vary widely as well.

HF transceivers are often equipped with a variety of different filters. The advantage of having multiple receive bandwidth choices on a multimode transceiver is that it permits noise or interference reduction by selecting a bandwidth matching the mode. (T4B08) For example, 2400 Hz is an appropriate receive filter to select in order to minimize noise and interference for SSB reception. (T4B09) 500 Hz is an appropriate receive filter to select in order to minimize noise and interference for CW reception. (T4B10)

2014 Tech study guide: station setup

There were two question changes in this section. Question T4A02 was changed from a question about headphones to a question about using computers in the shack. Question T4A05 was changed from a question about band-reject filters to one about using an SWR meter. I’ve added that question to the appropriate section…Dan

When setting up an amateur radio station, choosing the radio itself is the most important consideration, but you must also choose a wide range of accessories, such as power supplies and microphones. In addition, how you set up the station is important for it to operate efficiently.

One accessory that you’ll definitely need is a power supply to provide the DC voltage and current that your radio needs. A good reason to use a regulated power supply for communications equipment is that it prevents voltage fluctuations from reaching sensitive circuits. (T4A03) When choosing a supply, check the voltage and current ratings of the supply and be sure to choose one capable of supplying a high enough voltage and enough current to power your radio.

If you are going to operate with one of the voice modes, you’ll need a microphone. When considering the microphone connectors on amateur transceivers, note that some connectors include push-to-talk and voltages for powering the microphone. (T4A01)

A computer has become a very common accessory in an amateur radio “shack.” All of these choices are correct when talking about how a computer be used as part of an amateur radio station (T4A02):

  • For logging contacts and contact information
  • For sending and/or receiving CW
  • generating and decoding digital signals

If you plan to operate packet radio, you will need a computer and a terminal controller, or TNC, in addition to the radio. A terminal node controller would be connected between a transceiver and computer in a packet radio station. (T4A06) The TNC converts the ones and zeroes sent by the computer into tones sent over the air.

A more modern way to operate digital modes, such as RTTY or PSK-31, is to use a computer equipped with a sound card. When conducting digital communications using a computer, the sound card provides audio to the microphone input and converts received audio to digital form. (T4A07) The sound card may be connected directly to the radio, but it’s usually better to connect it through a device that isolates the radio from the computer. This prevents ground loops from causing the signal to be noisy.

Audio and power supply cables in a amateur radio station sometimes pick up stray RF. At minimum, this RF can cause the audio to be noisy. At worst, it can cause a radio or accessory to malfunction. To reduce RF current flowing on the shield of an audio cable (or in a power supply cable), you would use a ferrite choke. (T4A09)

Modern radio equipment is very well-designed, and harmonic radiation is rarely a problem these days. Even so, there may be times when it does become a problem, and you’ll have to take steps to attenuate the harmonics. To reduce harmonic emissions, a filter must be installed between the transmitter and the antenna. (T4A04)

Good grounding techniques can help you avoid interference problems. When grounding your equipment, you should connect the various pieces of equipment to a single point, keep leads short, and use a heavy conductor to connect to ground. Flat strap is the type of conductor that is best to use for RF grounding. (T4A08)

If you plan to install a radio in your car and operate mobile, you have a different set of challenges. One is connecting the radio to the car’s power system. Some amateurs connect their radio with a cigarette lighter plug, but this plug is not designed for high currents. Instead, a mobile transceiver’s power negative connection should be made at the battery or engine block ground strap. (T4A11) The positive connection can also be made at the battery or through an unused position of the vehicle’s fuse block.

Another challenge is noise generated by the car itself. One thing that could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter is that noise on the vehicle’s electrical system is being transmitted along with your speech audio. (T4A12)

The alternator is often the culprit.  The alternator is the source of a high-pitched whine that varies with engine speed in a mobile transceiver’s receive audio. (T4A10) Should this be a problem, there are filters that you can install to mitigate the alternator whine. One thing that would reduce ignition interference to a receiver is to turn on the noise blanker. (T4B05)

2014 Tech study guide: electrical safety

Several changes were made to this section that I don’t like. For example, the question pool committee removed the question about 30V being the commonly accepted value for the lowest voltage that can cause a dangerous electric shock. The question about 100 mA being the lowest amount of electrical current flowing through the body that is likely to cause death was removed from the 2010 question pool, so now there are no questions at all about these values. I’m leaving them in the study guide, though, because I think they’re important.

The committee also removed the question about charging a 12 V battery by connecting it to your car battery and running the engine. I’m all for removing that question. It was replaced by a question about what might happen if you short the terminals of a 12V battery…Dan

BE SAFE!

When operating or working on amateur radio equipment, it’s possible to come into contact with dangerous voltages and currents. Because it would be a shame to lose a single person, it’s important to know how to be safe when working with electricity. Having said that, 30 volts is the commonly accepted value for the lowest voltage that can cause a dangerous electric shock, and 100 mA is the lowest amount of electrical current flowing through the body that is likely to cause death. These are not very large values.

All of these choices are correct when considering how current flowing through the body can cause a health hazard (T0A02):

  • By heating tissue
  • It disrupts the electrical functions of cells
  • It causes involuntary muscle contractions

Three-wire electrical outlets and plugs are safer than two-wire outlets and plugs, and you should use three-wire plugs for all of your amateur radio equipment. The third wire provides an independent, or safety ground. Safety ground is connected to the green wire in a three- wire electrical AC plug. (T0A03)

All of these choices are correct when choosing a good way to guard against electrical shock at your station (T0A06):

  • Use three-wire cords and plugs for all AC powered equipment
  • Connect all AC powered station equipment to a common safety ground
  • Use a circuit protected by a ground-fault interrupter

Individual pieces of equipment may have their own fuses to protect that piece of equipment should something happen that causes that equipment to draw excessive current. The purpose of a fuse in an electrical circuit is to interrupt power in case of overload. (T0A04) When replacing a fuse, always replace the blown fuse with a fuse of the same type and value. It is, for example, unwise to install a 20-ampere fuse in the place of a 5-ampere fuse because excessive current could cause a fire. (T0A05)

If you plan to build your own equipment, be sure to include fuses in your designs. A fuse or circuit breaker in series with the AC “hot” conductor should always be included in home-built equipment that is powered from 120V AC power circuits. (T0A08)

Whenever you’re working on equipment, be sure to disconnect it from the power lines, and even then be careful working around a power supply’s capacitors. If a power supply is turned off and disconnected, you might receive an electric shock from stored charge in large capacitors. (T0A11)

Finally, it’s necessary to take precautions when using batteries to power your amateur radio station. Conventional 12-volt storage batteries present several safety hazards. Shorting the terminals can cause burns, fire, or an explosion (T0A01), explosive gas can collect if not properly vented (T0A09), and, if a lead-acid storage battery is charged or discharged too quickly, the battery could overheat and give off flammable gas or explode. (T0A10)

2014 Tech study guide: modulation modes, signal bandwidth

The only change to this section i s that the answer to question T8A09 was changed from “between 5 and 10 kHz” to “between 10 and 15 kHz.”

When you get your Technician license, chances are FM is the type of modulation that you’ll use first. Frequency modulation, or FM, is the type of modulation most commonly used for VHF and UHF voice repeaters. (T8A04) FM is also the type of modulation most commonly used for VHF packet radio transmissions. (T8A02)

Single sideband, or SSB, is the type of voice modulation most often used for long-distance or weak signal contacts on the VHF and UHF bands. (T8A03) Single sideband is a form of amplitude modulation. (T8A01) A single-sideband signal may be upper- or lower-sideband. Upper sideband is normally used for 10 meter HF, VHF and UHF single-sideband communications. (T8A06)

The primary advantage of single sideband over FM for voice transmissions is that SSB signals have narrower bandwidth. (T8A07) The approximate bandwidth of a single sideband voice signal is 3 kHz. (T8A08) The approximate bandwidth of a VHF repeater FM phone signal is between 10 and 15 kHz. (T8A09)

Morse Code, or CW, is the type of emission that has the narrowest bandwidth. (T8A05) The approximate maximum bandwidth required to transmit a CW signal is 150 Hz. (T8A11) International Morse is the code used when sending CW in the amateur bands. (T8D09) All of these choices are correct when talking about instruments used to transmit CW in the amateur bands (T8D10):

  • Straight Key
  • Electronic Keyer
  • Computer Keyboard

Some modes have very wide bandwidths. The typical bandwidth of analog fast-scan TV transmissions on the 70 cm band, for example, is about 6 MHz. (T8A10) The type of transmission indicated by the term NTSC is an analog fast scan color TV signal. (T8D04)

2014 Tech study guide: SWR and antenna measurements

In the 2010 study guide, this section was part of the section on feedlines and connectors. I think it makes more sense to separate it like I have here. There is one added question in this section T7C13 asks what a dummy load consists of…Dan

Standing wave ratio is a term you’ll often hear when talking about antennas and feedlines. In general terms, standing wave ratio (SWR) is a measure of how well a load is matched to a transmission line. (T7C03) In this context, the “load” is the antenna. When we say that an antenna is matched to a transmission line, we mean that the impedance of the transmission line is equal to the impedance of the antenna.

The reason it is important to have a low SWR in an antenna system that uses coaxial cable feedline is to allow the efficient transfer of power and reduce losses. (T9B01) The bigger the mismatch is between the feedline and the load, the higher the SWR will be, and the more power you will lose in the feedline. Power lost in a feedline is converted into heat. (T7C07) Power converted into heat is not radiated by the antenna, meaning your radiated signal will be weaker.

You can measure the SWR of your antenna system with an SWR meter. You usually connect the SWR meter near the output of your transmitter because it is important to have a low SWR at that point. A directional wattmeter is an instrument other than an SWR meter that you could use to determine if a feedline and antenna are properly matched. (T7C08)

1 to 1 is the reading on an SWR meter indicates a perfect impedance match between the antenna and the feedline. (T7C04) 2 to 1 is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power. (T7C05) An SWR reading of 4:1 means that there is an impedance mismatch. (T7C06)

One way to ensure that the impedance of the antenna system matches the output impedance of transmitter is to use an antenna tuner. An antenna tuner matches the antenna system impedance to the transceiver’s output impedance. (T9B04)

In addition to the SWR meter and the directional wattmeter, there are a couple of other types of test instruments commonly found in an amateur’s “shack.” One instrument that every shack should have is the dummy load. A dummy load consists of a non-inductive resistor and a heat sink. (T7C13) The primary purpose of a dummy load is to prevent the radiation of signals when making tests. (T7C01)

Another common test instrument is the antenna analyzer. An antenna analyzer is an instrument that can be used to determine if an antenna is resonant at the desired operating frequency. (T7C02) You can also make a number of other measurements that will help you set up an antenna system, such as SWR, capacitance, and inductance.