Here's a post that's mostly for my own studies, but I hope others will find it useful. Today's topic is waves.
AC signals are described using a sine wave (from high school geometry). Anything above 0 on the typical graph is positive and below is negative. One full cycle of a sine pattern is called the cycle. The number of cycles per second is the frequency, which is measured in Hertz (Hz). The inverse of the frequency is the period, which is measured in seconds. For example, a wave with a frequency of 3 Hz cycles 3 times per second; it also has a period of 1/3 seconds.
The wavelength of a wave is the distance that is has traveled in one cycle. Wavelength is usually measured in meters and is represented by the Greek lambda (λ). Wavelength is the speed (usually the speed of light, c) divided by frequency. Remember that c is a constant, so we don't need to calculate for it.
λ = c / f
f = c / λ
We can use the old D=R*T equation from middle school on this one. The rate is c, which is the speed of light. The time is the period, which is the inverse of frequency, so, instead of multiplying by period, we can divide by frequency.
Since the speed of light is constant, it is common to have a wave talked about in terms of frequency or of wavelength. A 3MHz wave can be referred to as a 100m wave.
If capactive and inductive reactance cancel each other, you have resonance.
Radio frequencies: > 20kHz
Audio frequencies: <> 1GHz
A band is a range of frequencies used for a specific purpose. For example, the frequencies that ham operators use is called the amateur or ham bands.
The phase is the position with a cycle. If you are 180 degrees out of phase, you are out of phase.
Modulation is modifying a wave to by adding information to it.
In amplitude modulation (AM), the carrier wave is modified by the amplitude of the information it to create small peaks and valleys above the carrier wave. The carrier is then subtracted from the resulting wave to get the information out. This process is called demodulation. Any signal above the carrier wave is called the upper sideband (USB); any lower is the lower sideband (LSB). The sidebands contain the information!
If you had a 1MHz carrier and wanted to carry voice, what would the sidebands be? Voice goes up to about 3kHz, so, if you added and subtracted that from the 1MHz carrier, you would have a LSB of 997kHZ and a USB of 1003kHz (1.003MHz).
AM is very inefficient. Most of the power is dedicated to the carrier and two sidebands (which are mirrors of each other). A single sideband (SSB) is a signal with the carrier and one of the sidebands removed. This is much more efficient since the power is dedicated to the data and not the carrier or other sideband. UHF and VHF use the USB of the signal.
Modulation modes that change the frequency to add the information is frequency modulation (FM). When information is put on the carrier wave, the frequency deviates to include the information. Amplitude is not changed in FM transmission, making it a constant power signal. FM has many sidebands that range from 5 to 15 kHz. FM is popular because interference actually generates changes in amplitude, which can be filtered out with a limiter.
Modulation modes that change the phase of a wave when information is added is called phase modulation (PM).
Data can be transferred over the air by using data modes. A modem changes data to audible signals, and, on the other end, another modem demodulates. Protocols swch as RTTY, AX.25, B2F, PSK31, MFSK, AMTOR, and PACTOR all combine with a modulation to take care of errors and loss. A terminal node controller (TNC) is a microprocessor that processes the protocols along with a modem. A multiple protocol controller (MPC) is a TNC that does many protocols.
Saturday, July 24, 2010
Electrical Components
Here's a post that's mostly for my own studies, but I hope others will find it useful. Today, we're studying electrical components and their functions.
Resistors control the flow of electrons (current, I) through a medium. Resistors are rated in terms of resistance in Ohms. A variable resistor is called a potentiometer or pot.
Capacitors store energy. Capacitors are rated in terms of Farads (F) such as picofarads (pF) or microfarads (uF). They smooth out changes in voltage and are compared to a water tower. A water tower stores water and serves it to the community until it slowly runs out of water or until more water is pumped into it. The same goes for capacitors and electrons. Capacitors have no effect on AC current since it will be constantly filling and emptying as the current changes directions.
Inductors store magnetic energy like a capacitor stores electrical energy. Inductors are rated in terms of Henries (H) such as millihenries (mH). They smooth out changes in current (capacitors smooth voltage changes). When current is placed onto an inductor, the coil forms a magnetic field that builds until it reaches the max inductance for the inductors. The inductor then releases current at a steady rate.
Resistance to AC current is called reactance (signified by X) and is measured in Ohms. Capacitors are said to have capacitive reactance; inductors are said to have inductive reactance. The combination of capacitance and reactance is generally referred to as impendence.
Diodes allow current to flow in only one direction. If AC current is applied to a diode, the result is a DC current.
Transistors are doped so that small changes in voltage or current control larger voltages and currents. In other words, they can act as amplifiers if patterned correctly.
Integrated circuits (IC or chip) are combinations of active and passive components packaged together to do a particular task. Microprocessors are ICs.
Fuses interrupt excessive current by physically breaking the connection. Breakers do the same, but, instead of blowing up or melting, they trip and can be reset.
Ground-fault interrupters (GFIs) trip of it senses a current difference between hot and ground. If you drop the hair dyer in the tub, the ground side of the GFI will have a drop in current (since all the electrons are pouring out into the water), and the GFI will trip.
Surge protectors become resistors if the voltage gets above a certain level. This eliminated transient spikes. Lightning arrestors do the same job as surge protectors but are designed to take much higher currents and voltages.
Schematics are diagrams that describe a circuit. They use circuit symbols that represent the components and how they are connected together. Each symbol has a designator to name each component, like R1, R2, R3, RN for the resistors.
Resistors control the flow of electrons (current, I) through a medium. Resistors are rated in terms of resistance in Ohms. A variable resistor is called a potentiometer or pot.
Capacitors store energy. Capacitors are rated in terms of Farads (F) such as picofarads (pF) or microfarads (uF). They smooth out changes in voltage and are compared to a water tower. A water tower stores water and serves it to the community until it slowly runs out of water or until more water is pumped into it. The same goes for capacitors and electrons. Capacitors have no effect on AC current since it will be constantly filling and emptying as the current changes directions.
Inductors store magnetic energy like a capacitor stores electrical energy. Inductors are rated in terms of Henries (H) such as millihenries (mH). They smooth out changes in current (capacitors smooth voltage changes). When current is placed onto an inductor, the coil forms a magnetic field that builds until it reaches the max inductance for the inductors. The inductor then releases current at a steady rate.
Resistance to AC current is called reactance (signified by X) and is measured in Ohms. Capacitors are said to have capacitive reactance; inductors are said to have inductive reactance. The combination of capacitance and reactance is generally referred to as impendence.
Diodes allow current to flow in only one direction. If AC current is applied to a diode, the result is a DC current.
Transistors are doped so that small changes in voltage or current control larger voltages and currents. In other words, they can act as amplifiers if patterned correctly.
Integrated circuits (IC or chip) are combinations of active and passive components packaged together to do a particular task. Microprocessors are ICs.
Fuses interrupt excessive current by physically breaking the connection. Breakers do the same, but, instead of blowing up or melting, they trip and can be reset.
Ground-fault interrupters (GFIs) trip of it senses a current difference between hot and ground. If you drop the hair dyer in the tub, the ground side of the GFI will have a drop in current (since all the electrons are pouring out into the water), and the GFI will trip.
Surge protectors become resistors if the voltage gets above a certain level. This eliminated transient spikes. Lightning arrestors do the same job as surge protectors but are designed to take much higher currents and voltages.
Schematics are diagrams that describe a circuit. They use circuit symbols that represent the components and how they are connected together. Each symbol has a designator to name each component, like R1, R2, R3, RN for the resistors.
Thursday, July 22, 2010
Basic Electricity
Here's a post that's mostly for my own studies, but I hope others will find it useful.
Current is the flow of electrons. It is represented by the letter I. Current is measured in Amperes, which is represented by the unit A. Current is measured with an ammeter.
Voltage is the electro-motive force of electricity. It is represented by the letter E. Voltage is measured in Volts, which is represented by the unit V. Voltage is measured with a voltmeter. Voltage is measured from a reference voltage, which is usually ground. Voltage also has a polarity; positive polarity attracts electrons, while negative polarity repels them.
Resistance is the impedance of current. It is represented by the letter R. Resistance is measured in Ohms, which is represented by the unit Ω. Resistance is measured with an ohmmeter.
Ohm's Law defines the relationship among current (I), voltage (E), and resistance (R).
R = E / I
You can solve the equation for the others with some quick math.
E = R * I
I = E / R
Power is the product of voltage (E) and current (I). It is represented by the letter P. Power is measured in Watts, which is represented by the unit W. Power is not measured directly and must be calculated.
P = E * I
Again with some quick math.
E = P / I
I = P / E
Using the equations from Ohm's Law, we can substitute values for voltage (E) and current (I) in to the Power equation. Since E = R * I, we can say that P = (R * I) * I or RI^2. Also, since I = E / R, P = E * ( E / R), or E^2/R.
P = E^2 / R
P = R * I^2
Current is the flow of electrons. It is represented by the letter I. Current is measured in Amperes, which is represented by the unit A. Current is measured with an ammeter.
Voltage is the electro-motive force of electricity. It is represented by the letter E. Voltage is measured in Volts, which is represented by the unit V. Voltage is measured with a voltmeter. Voltage is measured from a reference voltage, which is usually ground. Voltage also has a polarity; positive polarity attracts electrons, while negative polarity repels them.
Resistance is the impedance of current. It is represented by the letter R. Resistance is measured in Ohms, which is represented by the unit Ω. Resistance is measured with an ohmmeter.
Ohm's Law defines the relationship among current (I), voltage (E), and resistance (R).
R = E / I
You can solve the equation for the others with some quick math.
E = R * I
I = E / R
Power is the product of voltage (E) and current (I). It is represented by the letter P. Power is measured in Watts, which is represented by the unit W. Power is not measured directly and must be calculated.
P = E * I
Again with some quick math.
E = P / I
I = P / E
Using the equations from Ohm's Law, we can substitute values for voltage (E) and current (I) in to the Power equation. Since E = R * I, we can say that P = (R * I) * I or RI^2. Also, since I = E / R, P = E * ( E / R), or E^2/R.
P = E^2 / R
P = R * I^2
Introductions
Hi. My name is Aaron, and I'm taking some time off from my career studies to get my ham radio licenses. I have a blog on networking stuff at my own place which I use to make study notes, so, as I go through my studies here, I thought I would do the same.
Naturally, I'm going to start with the technician license, so keep an eye out for the basic stuff that all you Elmers already know. For the record, I just read the term "Elmer" in a book and have no clue when to use it appropriately. :)
Talk to you guys on the air soon. I'm sure my jargon will be better in time.
Naturally, I'm going to start with the technician license, so keep an eye out for the basic stuff that all you Elmers already know. For the record, I just read the term "Elmer" in a book and have no clue when to use it appropriately. :)
Talk to you guys on the air soon. I'm sure my jargon will be better in time.
Subscribe to:
Comments (Atom)