DIY Engineering @DIYEngineering
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DIY Engineering @DIYEngineering
Mike Comer @mike_n8wc
@kb6nu great info! Back to radio after several years. Enjoy how the internet has enhanced enjoyment of a great radio hobby.
I recently bought an LC100A LC meter from eBay, like the one shown below. If you search eBay, you’ll find them on sale anywhere from $20 to $40. Yesterday, I finally got around to playing with it a little.
To power the device, you need to supply +5V. It comes with a cable that has a USB connector on one side and a power connector on the other. Obviously, it’s meant to be powered by a USB port. I used a power adapter that I purchased to charge an iPod. It worked great.
As a quick test, I measured the capacitance of ten 0.33 uF caps that I purchased for a project. I first measured the capacitance with the LC100A and then with the fancy-schmancy Keithley 2110 that I purchased about a year ago. Below are the results:
Now, this wasn’t a very scientific test, but I am pleased with the results. I also measured the value of some 330 uH chokes that I had. They all measured between 315 and 320 uH.
So, all in all, I think this is a good deal for the money. I’m looking forward to using it on some of my projects. The next step is to find a box to put this in. I’m surprised that no one seems to have found one yet.
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)
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.
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)
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)
Three questions in this section were updated. The answer to TD802 was changed from “Automatic Position Reporting System” to “Automatic Packet Reporting System.” T8D05 was changed from a kind of irrelevant question about Techs being able to use data in the 219 to 220 MHz range to one about an application of APRS. T8D11 was changed from a question about the parity bit to one about ARQ transmission….Dan
When hams talk about “digital modes,” we are talking about the ways in which we use a computer in conjunction with a radio to communicate with one another. They all involve sending digital data back and forth to one another. All of these choices are correct (examples of a digital communications method) (T8D01):
Packet radio was one of the first digital modes. It is called packet radio because the data to be sent from station to station is separated into a number of packets which are then sent separately by the transmitting station and received and re-assembled by the receiving station. All of these choices are correct when talking about what may be included in a packet transmission (T8D08):
- A check sum which permits error detection
- A header which contains the call sign of the station to which the information is being sent
- Automatic repeat request in case of error
Some amateur radio digital communications systems use protocols which ensure error-free communications. One such system is called an automatic repeat request, or ARQ, transmission system. An ARQ transmission system is a digital scheme whereby the receiving station detects errors and sends a request to the sending station to retransmit the information. (T8D11)
APRS is one service that uses packet radio. The term APRS means Automatic Packet Reporting System. (T8D02) A Global Positioning System receiver is normally used when sending automatic location reports via amateur radio. (T8D03) Providing real time tactical digital communications in conjunction with a map showing the locations of stations is an application of APRS (Automatic Packet Reporting System). (T8D05)
A popular digital mode on the HF bands is PSK. The abbreviation PSK means Phase Shift Keying. (T8D06) PSK31 is a low-rate data transmission mode. (T8D07)
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.