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.

2014 Tech study guide: types of feedline, connectors

In the 2010 study guide, I also included questions about SWR and antenna measurements in this section. For 2014, however, I’ve decided to make that a separate section…Dan

Feedlines connect radios to antennas. There are many different types of feedlines, but coaxial cable is used more often than any other feedline for amateur radio antenna systems because it is easy to use and requires few special installation considerations. (T9B03) A common use of coaxial cable is carrying RF signals between a radio and antenna. (T7C12) Note, however, that the loss increases as the frequency of a signal passing through coaxial cable is increased. (T9B05)

When choosing a feedline, it is important to match the impedance of the feedline to the output impedance of the transmitter and the input impedance of the antenna. Impedance is a measure of the opposition to AC current flow in a circuit. (T5C12) Ohms are the units of impedance. (T5C13)

Most amateur radio transmitters are designed to have an output impedance of 50 ohms. Because that is the case, the impedance of the most commonly used coaxial cable in typical amateur radio installations is 50 ohms. (T9B02)

RG-58 and RG-8 are two types of coaxial cable often used in amateur radio stations. Both have an impedance of 50 ohms, but there are important differences between the two. One electrical difference between the smaller RG-58 and larger RG-8 coaxial cables is that RG-8 cable has less loss at a given frequency. (T9B10) The type of coax that has the lowest loss at VHF and UHF is air-insulated hard line. (T9B11)

Moisture contamination is the most common cause for failure of coaxial cables. (T7C09) One way that moisture enters a cable is via cracks in the cable’s outer jacket. The reason that the outer jacket of coaxial cable should be resistant to ultraviolet light is that ultraviolet light can damage the jacket and allow water to enter the cable.(T7C10) A disadvantage of “air core” coaxial cable when compared to foam or solid dielectric types is that it requires special techniques to prevent water absorption. (T7C11)

PL-259 connectors are the most common type of connectors used on coaxial cables in amateur radio stations. One thing that is true of PL-259 type coax connectors is that they are commonly used at HF frequencies. (T9B07)

One problem with PL-259 connectors is that they are not the most suitable connector when operating at higher frequencies. Instead, a Type N connector is most suitable for frequencies above 400 MHz. (T9B06)

No matter what type of connector you use, coax connectors exposed to the weather should be sealed against water intrusion to prevent an increase in feedline loss. (T9B08) Also make sure to tighten connectors well. Also make sure that your antenna connections are tight and the connectors are soldered properly. A loose connection in an antenna or a feedline might cause erratic changes in SWR readings. (T9B09)

 

What’s up at KB6NU? Tech class, W1AW/x

On Saturday, I taught yet another one-day Tech class. It was supposed to be the biggest one yet. I generally like to limit the number of students to 20, so that the test session doesn’t last forever, but the response was so good that I enrolled 22, and then put several on a waiting list.

22 signed up for Saturday's one-day Tech class, but due to the weather, six were unable to attend.

22 signed up for Saturday’s one-day Tech class, but due to the weather, six were unable to attend.

Unfortunately, the weather here, like in many parts of the Midwest has just been crazy, and Friday night was no exception. We got about three or four inches of snow overnight, and six of the students were unable to make it. A couple of them tried, but I-94, the freeway they needed to take to get to Ann Arbor was closed in a couple of spots due to accidents. They got stuck in all that traffic.

One thing you might notice about this class is that the average age of the students is lower than the average age of the ham population. Most of the students in this class were in their 20s or 30s. Some were from the local hacker community. Some were college students. Who says that amateur radio doesn’t appeal to younger people?

There was a group of five or six guys who were all friends. One of their buddies who already had his ham license paid for all five of them. That was pretty cool.

When all was said and done, fifteen of the sixteen who attended passed the test. And, the one who failed missed it by only one question. So, overall, a pretty successful class this time.

After the test, three of the students went up to the shack at the museum to take pictures. Ovide, K8EV, was up there operating the station, and put them on the air. I caught up with them as we all were leaving, and they were all pretty geeked about making their first HF contact.

From left to right, the three VEs at Saturday's Tech class were George, K9TRV; Jeff, W8SGZ; and Mark, W8FSA. Thanks, guys!

From left to right, the three VEs at Saturday’s Tech class were George, K9TRV; Jeff, W8SGZ; and Mark, W8FSA. Thanks, guys!

11 Qs on a snowy Sunday

Sunday’s weather was not much better. That made it a good day to stay indoors and operate my own station. I made 11 contacts overall on Sunday, including:

  • a couple of South Americans on 10m,
  • W1AW/2 and W1AW/5, and
  • a couple more DX contacts on 40m in the evening.

The W1AW contacts were kind of amusing. I heard W1AW/2 calling CQ on 10108 kHz, listening up. Except that he wasn’t listening up. He was S9 here in Michigan, so I knew that he should be able to hear me, but after several CQs, it was apparent that he wasn’t hearing anyone. So, guessing that he wasn’t really listening up, I called him on the transmit frequency, and sure enough, he came back to me. He seemed a bit embarrassed that he had forgotten to turn on split operation.

A bit later, I ran into W1AW/5 on 30m and worked him. After tuning around a bit after that contact, I switched to 40m, and guess who was my first contact on 40? W1AW/5, of course! They’re in the log right next to one another.

2014 Tech study guide: antenna types, polarization

Three questions were added to this section, the question on antenna loading and two on mobile antenna installation. I think these are good changes…Dan

The most common, and perhaps the simplest, antenna is the half-wave dipole antenna. As the name suggests, it measures close to one half wavelength from one end of the antenna to the other. A simple dipole mounted so the conductor is parallel to the Earth’s surface is a horizontally polarized antenna. (T9A03) The direction that radiation is strongest from a half-wave dipole antenna in free space is broadside to the antenna. (T9A10)

The length of a dipole antenna is actually about 5% shorter than the value that you would calculate using the formula wavelength in meters equals 300 divided by frequency in megahertz. The reason for this is that the velocity of a radio wave through wire is lower than the velocity of the wave in free space. Consequently, the approximate length of a 6 meter 1/2-wavelength wire dipole antenna is 112 inches. (T9A09) To make a dipole antenna resonant on a higher frequency, you would shorten it. (T9A05)

Perhaps the second-most popular type of amateur radio antenna is the quarter-wave vertical antenna. For vertical antennas, the electric field is perpendicular to the Earth. (T9A02) This makes them vertically-polarized antennas. The approximate length of a quarter-wavelength vertical antenna for 146 MHz is 19 inches. (T9A08)

Because HF antennas can be very long, many amateurs use a technique called “loading” to shorten them. Loading, when referring to an antenna, means inserting an inductor in the radiating portion of the antenna to make it electrically longer. (T9A14)

Another popular type of antenna is the beam antenna. A beam antenna is an antenna that concentrates signals in one direction. (T9A01) The quad, Yagi, and dish antennas are directional antennas. (T9A06) The gain of an antenna is the increase in signal strength in a specified direction when compared to a reference antenna. (T9A11)

Most hand-held VHF and UHF transceivers come with what’s called a “rubber duck” antenna. A disadvantage of the “rubber duck” antenna supplied with most handheld radio transceivers is that it does not transmit or receive as effectively as a full-sized antenna. (T9A04) A good reason not to use a “rubber duck” antenna inside your car is that signals can be significantly weaker than when it is outside of the vehicle. (T9A07)

A better option is to use an externally-mounted antenna. VHF or UHF mobile antennas are often mounted in the center of the vehicle roof because a roof mounted antenna normally provides the most uniform radiation pattern. (T9A13) Many mobile installations use a 5/8-wavelength vertical antenna. One reason to use a properly mounted 5/8 wavelength antenna for VHF or UHF mobile service is that it offers a lower angle of radiation and more gain than a 1/4 wavelength antenna and usually provides improved coverage. (T9A12)

2014 Tech study guide: schematics and components (part 4)

My study guide covers the questions in T6C and T6D of the question pool in four separate sections. Overall, the question pool committee added several questions to T6C and T6D. In this section, T6D12 is an added question…Dan

There are many different types of components in modern radio equipment. Below, we will describe the types of components you will need to know about to pass the Technician Class license examination.

A relay is a switch controlled by an electromagnet. (T6D02)

Meters are devices used to indicate many different values. For example, a meter can be used to display signal strength on a numeric scale. (T6D04) Meters are also used to indicate the output voltage of a power supply, the output power of a transmitter, and many other parameters.

Integrated circuit is the name of a device that combines several semiconductors and other components into one package. (T6D09) Integrated circuits may perform either analog or digital functions. One type of analog integrated circuit that is very common is the voltage regulator. A regulator is the type of circuit that controls the amount of voltage from a power supply. (T6D05)

An LED is commonly used as a visual indicator. (T6D07) LED is short for light-emitting diode. They come in a variety of colors.

When connecting electronic assemblies together, we often use cables with one or more conductors. Some of those conductors may have a shield around them that is connected to ground. A common reason to use shielded wire is to prevent coupling of unwanted signals to or from the wire. (T6D12)

2014 Tech study guide: schematics and components (part 3)

T3

My study guide covers the questions in T6C and T6D of the question pool in four separate sections. Overall, the question pool committee added several questions to T6C and T6D. In this section, T6D11 is an added question…Dan

The circuit shown in Figure T3 is the output circuit of a transmitter. Component 3 in figure T3 is a variable inductor. (T6C10)

There are two variable capacitors in this circuit—component 2 and the unlabeled component. A capacitor is used together with an inductor to make a tuned circuit. (T6D08)

Component 4 in figure T3 is an antenna. (T6C11)

An inductor and a capacitor connected in series or parallel to form a filter is a simple resonant or tuned circuit. (T6D11) When the capacitor and inductor are connected in series, the circuit has a very low impedance at the resonant frequency. When the capacitor and inductor are connected in parallel, the circuit has a very high impedance at the resonant frequency.

2014 Tech study guide: schematics and components (part 2)

My study guide covers the questions in T6C and T6D of the question pool in four separate sections. Overall, the question pool committee added several questions to T6C and T6D, but in part 2 below, all of the questions and answers are the same as in the 2010 question pool…Dan

The circuit shown in Figure T2 is a simple power supply. Component 2 is a fuse.

T2

Component 3 in figure T2 represents a single-pole single-throw switch. (T6D03) It turns the power supply on and off.

Component 4 in figure T2 is a transformer. (T6C09) A transformer is commonly used to change 120V AC house current to a lower AC voltage for other uses. (T6D06)

A rectifier changes an alternating current into a varying direct current signal. (T6D01) Component 5 in Figure T2 is a rectifier diode.

Component 6 in figure T2 is a capacitor. (T6C06) It is a filter capacitor, whose function is to help filter out the 60 Hz component of the rectified AC.

Component 8 in figure T2 is a light emitting diode. (T6C07). It is a pilot light, serving to alert a user when the power supply is on.

Component 9 in figure T2  is a variable resistor. (T6C08) Its purpose is to limit the output current of the supply.

2014 Tech study guide: schematics and components (part 1)

My study guide covers the questions in T6C and T6D of the question pool in four separate sections. Overall, the question pool committee added several questions to T6C and T6D, but in part 1 below, all of the questions and answers are the same as in the 2010 question pool…Dan

Schematic symbols is the name for standardized representations of components in an electrical wiring diagram. (T6C01) The symbols on an electrical circuit schematic diagram represent electrical components. (T6C12) The way components are interconnected is accurately represented in electrical circuit schematic diagrams. (T6C13) T1 Figure T1 is a schematic diagram of a simple circuit that turns on a lamp when a positive voltage is applied to the input. Component 1 in figure T1 is a resistor. (T6C02) Its function is to limit the input current.

Component 2 in figure T1 is a transistor. (T6C03) Its function is to switch the current through the lamp on and off. The function of component 2 in Figure T1 is to control the flow of current. (T6D10)

Component 3 in figure T1 is the lamp. (T6C04) Component 4 in figure T1 is a battery. (T6C05) This battery supplies the current that lights the lamp.

2014 Tech study guide: math for electronics

Below is the “Math for electronics” section of the 2014 edition of the No-Nonsense Technician Class License Study Guide. As always, comments welcome…Dan

When dealing with electrical parameters, such as voltage, resistance, current, and power, we use a set of prefixes to denote various orders of magnitude:

  • milli- is the prefix we use to denote 1 one-thousandth of a quantity. A milliampere, for example, is 1 one-thousandth of an ampere, or .001 A. Often, the letter m is used instead of the prefix milli-. 1 milliampere is, therefore, 1 mA.
  • micro- is the prefix we use to denote 1 millionth of a quantity. A microvolt, for example, is 1 millionth of a volt, or .000001 V. Often you will see the Greek letter mu, or μ, to denote the prefix micro-. 1 microvolt is, therefore, 1 μV.
  • pico- is the prefix we use to denote 1 trillionth of a quantity. A picovolt is 1 trillionth of a volt, or .000001 μV.
  • kilo- is the prefix we use to denote 1 thousand of a quantity. A kilovolt, for example, is 1000 volts. Often, the letter k is used instead of the prefix kilo-. 1 kilovolt is, therefore, 1 kV.
  • mega- is the prefix we use to denote 1 million of a quantity. A megahertz, for example, is 1 million Hertz. The unit of frequency is the Hertz. (T5C05) It is equal to one cycle per second. Often, the letter M is used instead of the prefix mega-. 1 megahertz is, therefore, 1 MHz.

Here are some examples:

  • 1,500 milliamperes is 1.5 amperes. (T5B01)
  • Another way to specify a radio signal frequency of 1,500,000 hertz is 1500 kHz.
    (T5B02)
  • One thousand volts are equal to one kilovolt. (T5B03)
  • One one-millionth of a volt is equal to one microvolt. (T5B04)
  • If an ammeter calibrated in amperes is used to measure a 3000-milliampere current,
    the reading it would show would be 3 amperes. (T5B06)
  • If a frequency readout calibrated in megahertz shows a reading of 3.525 MHz, it would
    show 3525 kHz if it were calibrated in kilohertz. (T5B07)
  • 1 microfarad is 1,000,000 picofarads. (T5B08) (Farad is the unit for capacitance.)
  • 28.400 MHz is equal to 28,400 kHz. (T5B12)
  • If a frequency readout shows a reading of 2425 MHz, the frequency in GHz is 2.425 GHz. (T5B13)

When dealing with ratios—especially power ratios—we often use decibels (dB). The reason for this is that the decibel scale is a logarithmic scale, meaning that we can talk about large ratios with relatively small numbers. At this point, you don’t need to know the formula used to calculate the ratio in dB, but keep in mind the following values:

  • 3 dB is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts. (T5B09) This is a ratio of 2 to 1.
  • -6 dB is the approximate amount of change, measured in decibels (dB), of a power decrease from 12 watts to 3 watts. (T5B10) This is a ratio of 4 to 1.
  • 10 dB is the approximate amount of change (actually it is the EXACT amount of change), measured in decibels (dB), of a power increase from 20 watts to 200 watts. (T5B11) This is a ratio of 10 to 1.

Should amateur radio operators know how to use the Internet?

My No-Nonsense Technician Class License Study Guide is available for free here on KB6NU.Com

My No-Nonsense Technician Class License Study Guide is available for free here on KB6NU.Com

Often, I get requests from hams teaching courses to print a number of copies of my No-Nonsense Technician Class Amateur Radio License Study  Guide. I normally reply that individuals are free to download and print the study guide if they like, but that I don’t usually give permission to print out many copies. There are a couple of reasons for this, the main one being that when individuals each download their own copies, I get a better indication of how many are actually using it.

Sometimes, they’ll come back and say that the reason they’re asking for permission to print copies is that some of the students aren’t very Internet-savvy, and that they may not know how to get on my website and download the study guide. That, of course, begs the question, “Should amateur radio operators know how to use the Internet?”

The NCVEC question pool committee obviously thinks so. There are a number of questions on the test about IRLP and EchoLink, both of which use the Voice Over Internet Protocol (VOIP) to allow communications over the Internet.

Don’t get me wrong. I love it that folks want to use my study guide, and I will continue to make it free for as long as I continue to produce it. It seems to me, however, that knowing how to use the Internet is now a basic skill that every ham should have. That being the case, I’m going to continue to ask that teachers that want to use my study have their students download it from my website and not print copies for them.