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: semiconductors

The Question Pool committee made several changes to the questions in this chapter. I like the changes. They make it easier to understand the idea of a transistor, I think…Dan

A diode is an electronic component that allows current to flow in only one direction. (T6B02) Diodes have only two electrodes. Anode and cathode are the names of the two electrodes of a diode. (T6B09) A semiconductor diode’s cathode lead is usually identified with a stripe. (T6B06)

Light-emitting diodes are a particular type of diode. When current flows through them, they emit visible light, making them useful as indicators and as part of digital readouts. The abbreviation “LED” stands for Light Emitting Diode. (T6B07)

Transistors are electronic components capable of using a voltage or current signal to control current flow. (T6B01) The transistor is a component that can be used as either an electronic switch or amplifier. (T6B03) Gain is the term that describes a transistor’s ability to amplify a signal. (T6B12) The transistor is an electronic component that can amplify signals. (T6B05)

A transistor is a component made of three layers of semiconductor material. (T6B04) Bipolar junction transistors have layers that are either P-type, which means that it has a positive net charge, or N-type, which means it has a net negative charge. Each layer has an electrode, making the transistor a device with three leads.

There are two types of bipolar junction transistors: PNP or NPN. A PNP transistor has two P layers, with an N layer sandwiched between them. An NPN transistor has two N layers, with a P layer sandwiched between them. The three electrodes of a PNP or NPN transistor are the emitter, base, and collector. (T6B10)

Another type of transistor often found in amateur radio equipment is the field-effect transistor. The abbreviation “FET” stands for Field Effect Transistor. (T6B08) FETs, like NPN and PNP transistors have three leads. Source, gate, and drain are the three electrodes of a field effect transistor. (T6B11)

2014 Tech study guide: resistors, capacitors and capacitance, inductors and inductance, batteries

Below is the “Electronics principles and components: resistors and resistance, capacitors and capacitance, inductors and inductance, batteries” section of the 2014 edition of the No-Nonsense Technician Class License Study Guide. As always, comments welcome…Dan

A resistor is the electrical component used to oppose the flow of current in a DC circuit. (T6A01) Most resistors have a fixed value, which is specified in ohms.

Some resistors are variable, that is you can change the resistance of the resistor by turning a shaft or sliding a control back and forth. These variable resistors are called potentiometers. A potentiometer is the type of component that is often used as an adjustable volume control. (T6A02) Resistance is the electrical parameter that is controlled by a potentiometer. (T6A03)

The type of electrical component that consists of two or more conductive surfaces separated by an insulator is a capacitor. (T6A05) A capacitor is the electrical component that stores energy in an electric field. (T6A04) Capacitance is the ability to store energy in an electric field. (T5C01) The farad is the basic unit of capacitance. (T5C02)

The type of electrical component that stores energy in a magnetic field is an inductor. (T6A06) The electrical component that is usually composed of a coil of wire is an inductor. (T6A07) The ability to store energy in a magnetic field is called inductance. (T5C03) The henry is the basic unit of inductance. (T5C04)

A switch is the electrical component used to connect or disconnect electrical circuits. (T6A08)

A fuse is the electrical component used to protect other circuit components from current overloads. (T6A09)

As amateur radio operators, we often use batteries to power our radio equipment. Some types of batteries are rechargeable, while others are not. The battery type that is not rechargeable is the carbon-zinc battery. (T6A11) All of these choices are correct when talking about battery types that are rechargeable (T6A10):

  • Nickel-metal hydride
  • Lithium-ion
  • Lead-acid gel-cell

From my Twitter feed: space weather, SDR, trigonometry?

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Everything you ever wanted to know about #space #weather in 1 great guide (pdf) 1.usa.gov/19VPZMF via @NWS #SWPC pic.twitter.com/GBsY52qqCE
 

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RTL-SDR Now Supported by MATLAB rtl-sdr.com/rtl-sdr-now-su…

 

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What do farmers use when calculating trig equations? Swine and Coswine

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.

2014 Tech study guide: DC power calculation

Below is the “DC power calculation” section of the 2014 edition of the No-Nonsense Technician Class License Study Guide. This section is mostly unchanged from the last edition. As always, comments welcome…Dan

Power is the rate at which electrical energy is generated or consumed. The formula used to calculate electrical power in a DC circuit is power (P) equals voltage (E) multiplied by current (I). (T5C08)

P= E × I

138 watts is the power being used in a circuit when the applied voltage is 13.8 volts DC and the current is 10 amperes. (T5C09)

P = E × I = 13.8 V × 10 A = 138 W

When the applied voltage in a circuit is 12 volts DC and the current is 2.5 amperes, the power being used is 30 watts. (T5C10)

P = E × I = 12 V × 2.5 A = 30 W

Just as with Ohm’s Law, you can use algebra to come up with other forms of this equation to calculate the voltage if you know the power and the current, or to calculate the current if you know the power and the voltage. The formula to calculate the current, if you know the power and the voltage is

I = P / E

For example, 10 amperes are flowing in a circuit when the applied voltage is 12 volts DC and the load is 120 watts. (T5C11)

I = P / E = 120 W / 12 V = 10 A

2014 Tech study guide: electrical principles, Ohm’s Law

As some of you may know, the Tech question pool is being updated this year. That means, of course, that I’ll have to update my study guide. 

Below are the first two sections. These are basically unchanged from the last edition, except that I removed the questions about voltmeter and ammeter from the first section and questions about calculating power from the second. This allows readers to focus on the electrical concepts. We’ll cover the voltmeter and ammeter questions, and the power calculation questions later.

pier-chartsI am considering adding the charts shown at right to aid people in remembering what formulas to use when calculating the various parmaters. What do you think? Should I add them, or would that just muddy the waters?

The study guide will show the correct answers in bold. I don’t know what the deal is, but for some odd reason, the bold text doesn’t really show as bold here on the website.

Electrical principles, units, and terms: current and voltage; conductors and insulators; alternating and direct current; resistance; power

You don’t have to be an electronics engineer to get a Technician Class license, but it does help to know the basics of electricity and some of the units we use in electronics. The most important concepts are current, voltage, resistance, power, and frequency.

Voltage is the force that causes electrons to flow in a circuit. Voltage is sometimes called electromotive force, or EMF. Voltage is the electrical term for the electromotive force (EMF) that causes electron flow. (T5A05) The volt is the basic unit of electromotive force. (T5A11)

The letter V is shorthand for volts. About 12 volts is the amount of voltage that a mobile transceiver usually requires. (T5A06)

Current is the name for the flow of electrons in an electric circuit. (T5A03) Electrical current is measured in amperes. (T5A01) Direct current is the name for a current that flows only in one direction. (T5A04) Batteries supply direct current, or simply DC.

Alternating current is the name for a current that reverses direction on a regular basis. (T5A09) Frequency is the term that describes the number of times per second that an alternating current reverses direction. (T5A12) Alternating current, or AC, is what is available from your home’s wall sockets. Power supplies convert the AC into DC, which is required for most modern amateur radio equipment.

Resistance is the term used to describe opposition to current flow in a circuit. The basic unit of resistance is the ohm. The Greek letter omega (?) is shorthand for ohms.

Conductors are materials that conduct electrical current well, or, in other words, have a low resistance. The copper wires that we use to connect a power supply to a radio are good conductors because copper is a good electrical conductor. (T5A07)

Insulators are materials that that have a high resistance. They do not conduct electrical current very well. Plastics and glass, for example, are good electrical insulators. (T5A08)

The term that describes the rate at which electrical energy is used (or generated) is power. (T5A10) Electrical power is measured in watts. (T5A02)

Ohm’s Law: formulas and usage 

Hams obey Ohm’s Law!

Ohm’s Law is the relationship between voltage, current, and the resistance in a DC circuit. When you know any two of these values, you can calculate the third.

The most basic equation for Ohm’s Law is

E = I × R

In other words, when you know the current going into a circuit and the resistance of the circuit, the formula used to calculate voltage across the circuit is voltage (E) equals current (I) multiplied by resistance (R). (T5D02)

When you know the voltage across a circuit and the resistance of a circuit, the formula used to calculate resistance in a circuit is resistance (R) equals voltage (E) divided by current (I). (T5D03) We can also write this formula as

R = E / I

When you know the voltage across a circuit and the resistance of a circuit, the formula used to calculate current in the circuit is current (I) equals voltage (E) divided by resistance (R). (T5D01) This formula is written

I = E / R

Examples
The resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts is 30 ohms. (T5D04)

R = E / I = 90 V / 3 A = 30 ?

The resistance in a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes is 8 ohms.(T5D05)

R = E / I = 12 V / 1.5 A = 8 ?

The resistance of a circuit that draws 4 amperes from a 12-volt source is 3 ohms. (T5D06)

R = E / I = 12 V / 4 A = 3 ?

The current flow in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms is 1.5 amperes. (T5D07)

I = E / R = 120 V / 80 ? = 1.5 A

The current flowing through a 100-ohm resistor connected across 200 volts is 2 amperes. (T5D08)

I = E / R = 200 V / 100 ? = 2 A

The current flowing through a 24-ohm resistor connected across 240 volts is 10 amperes. (T5D09)

I = E / R = 240 V / 24 ? = 10 A

The voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it is 1 volt. (T5D10)

E = I × R = 0.5 A × 2 ? = 1 V

The voltage across a 10-ohm resistor if a current of 1 ampere flows through it is 10 volts. (T5D11)

E = I × R = 1 A × 10 ? = 10 V

The voltage across a 10-ohm resistor if a current of 2 amperes flows through it is 20 volts. (T5D12)

E = I × R = 2 A × 10 ? = 20 V

SDR: Success this time

Back in May, I purchased a DVB-T mini-dongle to play around with software-defined radio (SDR). Unfortunately, I purchased the wrong type of dongle, and I couldn’t get it to work with any of the SDR software packages out there. The reason for this is that it the dongle did not use the Realtek RTL2832U.

A couple of months ago, I purchased another dongle, this time making sure to purchase the correct one. As you can see from the Amazon ad at right, this dongle cost less than 15 bucks. When I first got it, I was able to get it to run with the Windows laptop I was using down in the shack, but wasn’t able to get it to work with the Mac I use in my office. So, I put it aside, meaning to get back to it sooner or later.

Well, later came on Sunday, as about a foot of snow fell on outside. I downloaded an OSX port of the SDR program gqrx, and in short order, I was actually up and running, and listening to FM broadcast stations here in Ann Arbor. Very cool! I have since used it to listen to not only FM broadcasts, but also the local repeaters and the NOAA weather station on 162.55 MHz.

At first, I was pretty disappointed with the performance. That was the fault of the antenna, though. The antenna that came with the dongle is pretty much useless. What I did was to cut off the whip, solder on a couple of alligator clips and clip the coax to an FM broadcast dipole that came with a stereo I bought ages ago. If you don’t want to do this, you can purchase adapters cable, like the one shown at right, which have an SO-239 on one end and the MCX right angle connector, which plugs into the dongle on the other end.

That greatly improved the performance on FM broadcast as well as on 2m. I had planned on clipping to the 450-ohm ladder line J-pole that I have to see how it improves reception on 2m, but haven’t gotten around to that yet.

While gqrx is a nice program, it does have some limitations. For example, you cannot set up “memories” and switch between them. So, switching frequencies can be somewhat of a hassle. It would also be nice to have a scan feature, so that I could set it up just like I do my handheld and scan all the local repeater frequencies. The good thing is that this program is still very much under development.

The support is really good, too. There is a  gqrx Google Group where I got a very quick answer to  a newbie question.

What else can you do with this dongle? Quite a bit as it turns out. Yesterday, while composing another blog post, I learned about an RTL-SDR spectrum analyzer using a BeagleBone Black, which I already happen to have, and its 7? Touchscreen cape. Again, very cool.

You need a blivet

Brad, AA1IP, wrote to the Glowbugs group:

Disappointed and grumpy because ol’ Sanitary Claus didn’t being you any radio-related presents? Put on your 22, get on your toes and tapdance out an order for a Blivet or Blivette to restore your holiday cheer!

For $9.87, you receive a small USPS Priority flat-rate mail carton– a Blivette– stuffed with miscellaneous electronic parts: some are old, some are new, some are used and removed from equipment, and some are blew, er, blue.

For $23.23, you receive a medium USPS Priority flat-rate mail carton– a Blivet– stuffed with the same contents as above, only more so.

Note that the price of a Blivet or Blivette includes  postage to U.S. addresses only. Overseas postage charges are steep.

Questions welcomed, PayPal honored. Please make sure that your PayPal invoice includes your preferred USPS delivery address.

Now go build a radio!

I just sent off for a Blivette. I’ll let you know what I get.

From my Twitter feed: Santa, kits, PCB design

HamHijinks's avatarHam Hijinks @HamHijinks
Trying a new mode tonight: Santa Scatter! #hamr #hamradio

 

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Chris Armstrong @RigolTechUSA
The Rise, Fall, and Rise of Electronics Kits | @IEEESpectrum #IEEE goo.gl/wzTuv1

ke9v's avatar
Jeff Davis @ke9v
Design it. Order it. Build it. Very cool. fplus.me/p/4wc8