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Episode 56 -- March 13th, 2017 -- Technician Class Ham License Exam prep, 2 of 3
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Metric System prefix review
Terra — one trillion
Giga — one billion
Mega — one million
Kilo — one thousand times
Milli — one thousandth of
Micro — one millionth of
Nano — one billionth of
Pico — one trillionth of
Higher Frequency = higher loss
Easy to use
not acceptable to interference from close metal objects
More expensive, especially for higher power handling
RG-8, RG-8X, RG-214
LMR 400, LMR 600
9913 or Hardline
Twinlead or ladder line
lower loss, if it is strung right
has to be looped if excess, can’t be near metal
Why is Low SWR important?
Protect the transmitter
Avoid stray RF energy around the ham shack — sometimes it can get into microphone and speaker wires and cause interference, even with good SWR. To avoid it getting into a Microphone, install one or more Ferrite chokes as a low pass filter on the mic cable.
Get the most of your signal out the antenna as possible
Common impedance is 50 ohms; “Characteristic Impedance”
How to measure
If you’re getting erratic readings, maybe a bad connector or water in the feed line
Sealed to prevent water from entering the feed line
PL-259 / SO-239 or UHF
commonly used at HF frequencies
Used by almost all ham radios
Different radios use different connectors for Power and Microphone. Most radios use the same connectors for external speakers and antennas
Preferred for microwave operation
Polarization matters around 20 DB Electric field = polarization. Magnetic field = perpendicular to polarization
Frequency and Wavelength
468 / freq in Mhz = total length in feet for a half wave dipole
Strongest Broadside to the antenna, weakest off the ends
Loading Coils to electrically lengthen an antenna
Traps on a dipole
Loading coil at the base of a vertical
Gain in reference to an isotropic antenna
You can either point an antenna directly at what you’re trying to reach or at an angle to bounce the signal off a mountain to reach your intended communication location
Beam or Yagi
Horizontal Polarization creates a tighter beam width so is used for SSB and long range whereas if you’re communicating with mobile stations such as on FM, Vertical polarization works better because that’s what they’re using
Angle of radiation is lower for ⅝ than a 1/4
Horizontal Radiation Pattern against grondplane
Magnetic field is parallel to the earth and the Electric field is perpendicular
Radio Wave Characteristics
Radio Waves are electromagnetic waves that travel through space. They contain an electric field and a magnetic field. This is Non-ionizing radiation as opposed to ionizing radiation, that you’d get from plutonium. RF radiation does not have sufficient energy to cause genetic damage
They bounce off the ionosphere
Radio waves travel at the speed of light
300 million meters per second = 5280 ft/sec
Wavelength x Frequency = speed of Radio Waves
So, 300 divided by frequency in MHz = # of meters wavelength
We use # of meters to identify radio bands
HF 3 - 30 MHz
VHF 30 - 300 MHz
UHF 300 - 3,000 MHz or .3 - 3 GHz
Reflections cause multipath distortion. Sometimes you get the signal bounced off one mountain and onother at the same time and since they’re different dx apart, they’ll heterodyne out of phase and distort — move a few quarter wavelengths left or right. When you’re driving through a rough patch, the fluttering is called, “Picket Fencing”
If you have a digital signal, distortion causes errors
Shorter wavelengths penetrate buildings better than longer ones
The FCC specifies a Maximum Permissible Exposure limit for radio waves being close to where people live. It depends on how big the antenna, how much power output from the transmitter and at what frequency you’re transmitting. Below 50 MHz they mostly don’t care so much
On the other hand, on 2m you need RF exposure evaluation if you’re sending more than 50 watts Peak Envelope Power to the antenna
Frequency and power level of the RF field, Distance from the antenna to a person and Radiation pattern of the antenna all contribute to the RF exposure evaluation.
The human body absorbs more RF energy at some frequencies than at others, particularly higher frequencies
You can determine that your station complies with FCC RF exposure regulations either By calculation based on FCC OET Bulletin 65 or By calculation based on computer or By measurement of field strength using calibrated equipment
If the distance between your antenna and a person became very small while you were transmitting, say, if they touched it, they might get a painful RF burn
If you think you might have a problem with RF exposure limits, the easiest first step is to Relocate antennas
If you make a change to your station, re-evaluate
Since the FCC guidelines for RF exposure limits are primarily concerned with average exposure of people to radiation you must try to factor in duty cycle or what % of the time you’re transmitting
The Ionosphere reflects waves below around 30 MHz most of the time
Radio waves travel along the ground, also, just about 15% further than how far you can see around the curvature of the earth. In fact, we use the term, “Radio Horizon” to refer to The distance over which two stations can communicate by direct path. Dust is irrelevant. Moisture helps a tiny bit.
It has up to 4 layers called, D, E F1 and F2
The E layer occasionally refracts VHF signals. Whenever you experience strong, over the horizon signals on 10, 6 and 2, chances are, it’s Sporadic E propagation.
auroral reflection happens sometimes. Signals vary rapidly and are usually distorted
Occasionally ground waves will refract around a mountain or other large obstruction. When this occurs, we call it Knife-edge diffraction.
Sometimes you can get over the horizon using VHF or even UHF around 300 miles. This is Tropospheric scatter or troposcatter up to 300 miles or so
When small rocks hit the earth and burn up, as they’re burning, they reflect radio waves. This happens most often on 6 meters. This is called, “Meteor Scatter”. Usually, one must use special digital modes to take advantage of the very short bursts of available path
Temperature inversions in the atmosphere cause Troposheric ducting. Radio waves get trapped between layers of the ionosphere. Discovered during WWII, they thought those super incredible frequencies up there at 144 MHz would just punch right through and would never be intercepted. They were wrong, it turns out. Relatively common in the summer, allows reception of signals up to 800 or 1000 or even 3000 miles away. Above 90 MHz happens more often. Works well over oceans.
During auroral reflection, VHF signals exhibit rapid fluctuations of strength and often sound distorted
The ionosphere fluctuates influence based on the 11 year sunspot cycle. When there’s a lot of sunspots, the ionosphere works better for hams and you can hear more signals. This is especially true on higher HF frequencies such as 6 and 10 meters at night, shortly before dawn is best.
If an FM receiver (such as the one in a Handitalkie) is just listening to a frequency, we don’t hear any hissing sound because of a radio feature called, “Squelch”. This mutes the speaker until an actual signal is heard, making our hobby more enjoyable. This is called, “Carrier squelch” meaning that a carrier or signal is required to open the receiver’s squelch so you can hear a transmission. The alternative is called “Tone Squelch” where a subaudible tone is inserted along side your voice while you transmit (nobody can hear it except the electronics) so that the receiver listens for that instead. This is called, Continuous Tone Coded Squelch System or CTCSS or sometimes just PL (an old trademark, “Private Line”) or “Buzz”.
Most VHF and UHF operation is on FM (instead of SSB or CW) through repeaters. A repeater listens on one channel and retransmits everything it hears on another channel. We say that it listens on it’s input frequency (the frequency on which you must transmit to use it) and it transmits on it’s output frequency or your receive frequency. Since it is a transmitter, we normally talk about a repeater’s “frequency” (just one) in terms of it’s transmit or your receive frequency.
Nobody can transmit and receive on the same frequency at the same time -they’d just hear themselves. So there are standard offsets in use for each band. The standard offset on 2m isPlus or minus 600 kHz. The standard offseton 70cm is 5 MHz. This is called, “Duplex” operation.
If you are so close to somebody that you can communicate with them directly without using the repeater, normally you would just use a single frequency upon which both of you would exchange transmissions. If you are communicating with somebody else using just 1 frequency for the two of you without a repeater, that is called, “Simplex” operation. The national simplex calling frequency on 2m is 146.52 MHz.
Since a repeater is an automatic system, if it accidentally transmits something which is against FCC rules, the responsible party is whoever made that transmission (assuming they did it on the input frequency). Otherwise, the repeater’s control operator is at fault.
Each repeater is licensed to a control operator whose callsign is sent (usually in morse code) periodically during transmissions through that repeater and that person is responsible for its operation.
Since anybody listening to a repeater can hear everybody who can talk on it easily (unlike on the HF bands where you don’t know if you can hear the other end or not) instead of calling CQ, you can just announce your callsign. Or say, “WB5QAL Listening”.
Since there are many more repeaters than there are frequencies on which to put them, sometimes, more than one repeater might share the same frequency. Hopefully, this only happens whey they are so far away that nobody can hear both. To choose which one you want to use, a so that you can use 1 tone for 1 repeater and a different CTCSS tone for another repeater and they (hopefully) won’t interfere with one another, even though they’re using the same frequency.
Some older repeaters just require an audio tone burst at the beginning of each transmission. Usually 1750 Hz is the frequency of the tone.
Some newer repeaters use a digital data packet at the beginning of each transmission to allow you to use their repeater, this is called, “Digital Coded Squelch” or DCS. There are a lot more DCS tones than CTCSS tones.
Talking through repeaters is an extremely reliable form of communication but it isn’t perfect.
If you’re driving, you might be right at the edge of a coverage area and you may start Picket Fencing. Wait and try again when you’re in a better location
Occasionally a radio transmitter can become out of adjustment if you bang it hard enough or change temperature too fast it it might be off frequency a little bit and require adjustment.
If your batteries get low, your signal might become distorted, but more than likely, people will hear the first half sentence of everything you say and then nothing afterwards. Charge your batteries.
There is often a 12 or 16 digit keypad on a radio or microphone for sending touch-tones or dual tone multifrequency (DTMF) tones. This is the old standard from AT&T in the 1970s by which phone calls were made from wired telephones after dials became obsolete. Hams use these tones for controlling repeaters, making phone calls over the radio (“Autopatch”) or setting up and taking down links (“IRLP”).
Because it is so reliable, it has been augmented using the internet in various ways. For example, we can use Voice Over IP Protocols (VOIP) to send voice signals received by a repeater to be sent using digital techniques over the internet to another repeater elsewhere. The most common are IRLP and Echolink
Echolink is a way for licensed hams to talk to a particular repeater using a website over the internet.
IRLP or Internet Relay Link Protocal is a system whereby repeaters are connected to the internet and you can use the 12 button keypad on your radio or microphone to “dial” a 4 or 5 digit “node ID” of another specific repeater to which you’d like to be linked and then carry on a conversation on your repeater with somebody on the other repeater. Everyone on both repeaters will overhear, but you’ll be able to converse and, when you’re done, “Hang up” and disconnect the two repeaters. Like a telephone system only your handitalkie is a handset.
Repeater Directories online and on paper list which IRLP nodes are active and working
An amateur radio station, such as an IRLLP capable repeater if it is connected to the internet is called a gateway.
Hams have a few satellites. Ham satellites have Transponders. A Transponder is like a repeater but instead of listening on just one frequency, it listens on a portion of a whole band and repeats the whole band portion on another band. If you have the license privilege to talk on the satellite’s input band, you can use one.
We use satellite tracking programs to see Maps showing the real-time position of the satellite track over the earth and The time, azimuth, and elevation of the start, maximum altitude, and end of a pass and The apparent frequency of the satellite transmission, including effects of Doppler shift.
time, azimuth and elevation
pass, LEO, geostationary
Doppler shift is An observed change in signal frequency caused by a change in distance between the satellite and the earth station. Think of a train whistle, changing its pitch as it comes closer and then goes farther away.
You should only use enough power to complete the contact
The ISS often has hams abord. If you have a technician license, and they’re available, you can talk with them.
Satellites often transmit information about themselves using a beacon.
Most satellites have more than one transponder. We talk about them by using terminology such as U/V to mean a UHF uplink and a VHF downlink. That is, in order for you to talk though a satellite transponder operating in U/V mode, you must transmit your SSB or CW or FM or FM packet digital signal on UHF (70cm) and receive the satellite’s transmissions of your signal and that of whoever responds to you on VHF, or 2 meters.
Satellites have a different kind of noise than normal radio communications. Rotation of the satellite and its antennas causes spin fading.
There are digital satellites which only work for FM Packet Radio
Some hams use computers
For logging contacts and contact information
For sending and/or receiving CW
encoding and decoding digital signals using a Terminal node controller or a sound card to the mic and speaker jacks of the radio
Seeing a graph in real time of the conditions of the band
Programming VHF and UHF radio frequencies from a spreadsheet like application
Seeing a map of APRS stations
In the car
Since most ham equipment runs off of 12vdc and most ham homes have 120vac, it stands to reason that most hams use regulated power supplies. The regulation prevents voltage fluctuations from reaching sensitive circuits which might otherwise make objectionable hum along with your transmissions
The alternator in your car produces square waves as it turns on and off as it rotates so it produces a lot of RF noise. On the radio, this sounds like high-pitched whine that varies with engine speed
When wiring a rig in the car, try to attach the ground wire At the battery or engine block ground strap
Just as you can adjust the volume control on your receiver so that it doesn’t distort the sound coming through your speaker, there is also a microphone gain control to adjust the level for different people to be able to talk clearly, some loud, some soft. If it’s turned up too loud, the sound might become distorted on transmit, too.
So you have a power supply and radio and mic and key connected perhaps through an amplifier and then an SWR meter and then perhaps through an antenna tuner and finally you’ll want to connect a filter to reduce harmonic emissionsBetween the transmitter and the antenna
Best to use a solid Flat strap for grounding the station to a ground rod
Another popular source of distortion while your listening to an AM or single sideband receiver is hash from power lines. Noise Blanker circuits are designed to mitigate this.
Automatic Gain Control is like an automatic volume control that keeps the signal the same loudness while you’re listening, even as it fades up and down in strength
The best way to hear signals on HF is to set your receiver bandwidth so that it only picks up a big enough chunk of the band to hear the signals you’re looking for. If that’s CW, then 250 or 500 Hz is plenty. For USB and LSB, you can get by with as little as 1.6 kHz, but normally 2400 Hz is considered optimal.
Nowadays, all HF radios have receive and transmit VFO and all VHF and UHF radios have computers controlling a frequency synthesizer so that you can use a keypad or knob to tune any channel and then store it in a memory channel for quick access
When you listen to a single sideband signal, as you turn your VHF knob, you’ll hear part of it then the center (where you’ll hear all of it) and then the other side. Because of this, all modern radios have RIT or Receiver Incremental Tuningto allow you to change your receive frequency but stay transmitting on the same frequency so the person with whom you’re conversing doesn’t chase you down or up the band.
In the old days, you’d have a receiver and a transmitter and they would each have a crystal to specify precisely what frequency upon which you could listen and talk. Later, everybody changed their receivers so that instead of a single crystal controlling a single local oscillator, there would be a variable capacitor to adjust a tuned circuit to change the frequency so that you could turn the VFO knob to hear stations on different frequencies.
If you charge or use up a lead-acid storage battery too fast, it can overheat and give off flammable gas or explode
If you Short the terminals, it can cause burns, fire, or an explosion
Electrical current flowing through a human body
physically heats tissue, like a microwave oven heats meat
disrupts the electrical functioning of cells
causes involuntary muscle contractions
The electricity coming into your home starts out as 3 phase 240 volt 60 cycle AC
Red and Black are hot
White is neutral - white to red and white to black are 120 vac
Green is ground
Fuses and circuit breakers exist to break a circuit rather than heat up wires beyond their capacity.
For example, if you have a circuit which requires a 5 amp fuse, that means that the wires in that circuit and other components can only accommodate up to 5 (or, more likely, 4 or less) amps. If you change that 5 amp fuse for a 20 amp fuse, that means that if a component fails and you accidentally end up with 19 amps flowing through the circuit, then those components the fuses is there to protect will fail instead of the fuse. If one of those components is a wire passing too close to something flammable, than that wire will heat up and possibly start a fire.
Guard against electrical shocks at your ham station:
Use 3 wire cords and plugs for all AC equipment and connect the ground wire to chassis ground
Connect all AC powered equipment in your station to a common ground
Plug it all into a GFCI outlet. “A GFCI is much more subtle. When you look at a normal 120-volt outlet in the United States, there are two vertical slots and then a round hole centered below them. The left slot is slightly larger than the right. The left slot is called "neutral," the right slot is called "hot" and the hole below them is called "ground." If an appliance is working properly, all electricity that the appliance uses will flow from hot to neutral. A GFCI monitors the amount of current flowing from hot to neutral. If there is any imbalance, it trips the circuit. It is able to sense a mismatch as small as 4 or 5 milliamps, and it can react as quickly as one-thirtieth of a second. So let's say you are outside with your power drill and it is raining. You are standing on the ground, and since the drill is wet there is a path from the hot wire inside the drill through you to ground (see How Power Distribution Grids Work for details on grounding). If electricity flows from hot to ground through you, it could be fatal. The GFCI can sense the current flowing through you because not all of the current is flowing from hot to neutral as it expects -- some of it is flowing through you to ground. As soon as the GFCI senses that, it trips the circuit and cuts off the electricity.” http://home.howstuffworks.com/question117.htm
According to a 1999 study by the American Society of Home Inspectors, 21% of GFCI circuit breakers and 19% of GFCI receptacles inspected didn't provide protection, leaving the energized circuit unprotected. In most cases, damage to the internal transient voltage surge protectors (metal-oxide varistors) that protect the GFCI sensing circuit were responsible for the failures of the protection devices. In areas of high lightning activity, such as southwest Florida, the failure rate for GFCI circuit breakers and receptacles was over 50%!
GFCIs will also fail if you wire them improperly. The most important thing to remember when wiring them is to connect the wire originating at the breaker to the line side of the GFCI and the wire connecting downstream to the load side of the device. The GFCI terminals are clearly marked “Line” and “Load.”.http://ecmweb.com/basics/how-gfcis-work
Mitigate lightning strikes on your antennas by grounding through lightning protectors such as gas-discharge type and ground all of them to the earth and each other.
When you build equipment which plugs into the wall (such as a power supply) always include a fuse or circuit breaker in series with the AC hot conductor
Remember that, if you build a power supply, it might have very big capacitors which store electrical energy, even when the power is removed it can shock you.
When working on a tower with others, always wear a hard hat and safety glasses because the FCC rules say you should. Safety glasses around a tower might be useful if you’re welding or looking up when somebody drops a screw, …ditto hard hat
Even climbing a tower, the FCC wants you to wear safety glasses with your climbing harness.
They also insist that you never do it alone, even if it’s just 20 feet up.
DO identify all the overhead electrical wires and place your mast or tower and antenna system so that, if it fell, it wouldn’t fall within 10 feet of the wires. Duh.
DO use a gin pole to lift tower sections because it is the easiest way to put up a tower if you don’t own a giant crane
DO NOT climb a telescoping or crank-up tower unless it is all the way retracted.
DO use a separate 8 ft ground rod for each leg of the tower and bond them to each other also. DON’T make sharp bends in the wires. DO Ensure that connections are short and direct
DO NOT use a utility pole to hold up your antenna because you might be a moron and place it in such a fashion as to accidentally touch high voltage wires if it were to blow away or break or fall.
Tower Grounding requirements are specified by local electrical codes