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Trade magazine articles: home lab equipment, antennas 101, AC grounding

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Here are some articles from the electronics trade magazines (well, online “magazines,” anyway) that I found interesting:

Equipment Recommendations for a Home Electronics Lab

Some of the author’s suggestions may seem a bit pricey for a radio amateur’s home lab, but good test equipment will yield good results. He writes:

With one exception, I like test equipment with knobs. That refers to scopes, signal sources, and power supplies. Siglent makes a nice, economical line of these kinds of instruments and they’re all available tomorrow via Amazon. You will probably need multiple power supplies, and you’ll want an old-school linear supply for audio work. Once upon a time, I’d have said buy only HP T&M gear (because I worked there, so I have a preference), and older HP gear from eBay can be nice, but the Siglent stuff comes with a warranty.”

Welcome to Antennas 101

In a very short space, the author does a pretty good job of explaining antennas and some of their parameters. For example, here’s how he explains antenna efficiency:

Antenna efficiency is like efficiency in general—the ratio of power out to power in. However, it’s designated in several different ways. In most cases, efficiencies account for the I2R losses, losses in any dielectric, and losses based on coupling to other devices. What may not be included is any loss related to antenna and transmission- line mismatch losses, resulting in reflected power and a higher SWR.

However, some measures of efficiency factor in any change in antenna radiation resistance variation. Most small antennas aren’t that efficient. Anything better than 50% to 60% is usually good, but always seek to improve it if you can.

AC grounding: essential, dangerous or both?

The first thing that the author of this piece does is to explain that, “A large part of the confusion comes from the ambiguous and this sloppy terminology associated with that innocent-sounding seven-letter word.” He then explains that the word ground can refer to any one of three types of circuit connections:

  • Earth ground where the circuit is actually connected to Earth, which acts as an infinite source and sink for electrons;
  • Common (may also be called signal ground), which establishes a 0-V point in a circuit (and there is often more than one of these in the circuit). It’s usually very misleading to even use the word ground with this one.
  • Chassis ground, which connects all nominally zero-volt potential points in a circuit; it may be connected to Earth ground, but often cannot be as there is no Earth ground for many devices such as most portable, battery-operated ones; here, it may be misleading to use the word ground if it is not connected to a real Earth ground.

The rest of the article is equally enlightening.

From the trade magazines: Automatic impedance matching, AC grounding, rechargeable batteries

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Automatic impedance matching in RF design

Impedance (Z) matching is an essential part of most RF circuit design. Regardless of what you’re designing, getting as much power to a load is a top target. Impedances must be matched to transfer the maximum amount of signal power between stages. And in power amplifiers (PAs), impedance matching is critical to getting the maximum power to the final load and maintaining PA linearity. Impedance matching to an antenna in a receiver or transmitter is an essential process.

Some loads are constant; thus, a single fixed Z-matching circuit can be used. But in other applications, that final load may change, or the frequency of operation will change, meaning that a fixed Z-match circuit will not produce the desired results. For these applications, a variable matching network that you can adjust is needed. Better still is a variable and automatic Z-match circuit that adjusts itself to the immediate load or frequency conditions.

Auto Z matching is more common than you think. If you own a recent smartphone, you’re probably using an auto Z-match antenna tuner. However, there are other applications. Here’s a primer on this topic for your elucidation and cogitation.

…read more

AC grounding: essential, dangerous, or both?

Most electrical engineers learn early-on about the importance of what are referred to as circuit grounds. In many cases, whatever your problem, adding a ground or improving the one you have (meaning lower impedance) is a good thing that can’t hurt. That’s what circuit EEs have drilled into them as they work and debug bench circuits prototypes, and more, and learn to connect the analog ground to the digital ground at one point only to minimize unwanted ground-current flow and associated noise.

In most cases, such grounding does improve circuit performance, but as every experienced engineer knows, every rule has legitimate exceptions, and grounding is one of them. A large part of the confusion comes from the ambiguous and this sloppy terminology associated with that innocent-sounding seven-letter word.

…read more

Rechargeable batteries enable greener electronics

While batteries provide untethered power, enabling convenience, dependability, and mobility, environmental responsibility suggests that rechargeable batteries have the same benefits, but can save money while reducing the amount of waste. This article examines the benefits offered by rechargeable battery technology, enabling us to make life better.

…read more

2020 Extra Class study guide: E4E – Noise suppression and interference: system noise; electrical appliance noise; line noise; locating noise sources; DSP noise reduction; noise blankers; grounding for signals; common mode currents

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Noise is often a real problem for radio amateurs. Fortunately, by understanding how noise is generated and how to reduce or eliminate it, noise can be tamed.

Atmospheric noise is naturally-occurring noise that appears across a wide bandwidth. To help you copy signals when there’s a lot of atmospheric noise, or any wide bandwidth noise, you can often use a receiver’s noise blanker. One undesirable effect that can occur when using a receiver’s IF noise blanker is that nearby signals may appear to be excessively wide even if they meet emission standards.

QUESTION: Which of the following signals might a receiver noise blanker be able to remove from desired signals? (E4E03)
ANSWER: Signals that appear across a wide bandwidth

QUESTION: What undesirable effect can occur when using an IF noise blanker? (E4E09)
ANSWER: Nearby signals may appear to be excessively wide even if they meet emission standards

Many modern receivers now use digital signal processing (DSP) filters to eliminate noise. The types of receiver noise that can often be reduced with a DSP noise filter, include broadband white noise, ignition noise, and power line noise.

QUESTION: Which of the following types of noise can often be reduced with a digital signal processing noise filter? (E4E02)
ANSWER: All these choices are correct

    • Broadband white noise
    • Ignition noise
    • Power line noise

Some receivers with DSP filter have an automatic notch filter, or ANF. An automatic notch filter recognizes interfering signals in the passband and attempts to set the notch to filter out that signal. When receiving CW signals, however, the filter may remove the CW signal as well as the interfering carrier.

QUESTION: What problem can occur when using an automatic notch filter (ANF) to remove interfering carriers while receiving CW signals? (E4E01)
ANSWER: Removal of the CW signal as well as the interfering carrier

While filters can be very effective at reducing noise, it is often better to figure out what is generating the noise and take steps to reduce or eliminate the amount of noise generated in the first place. Loud roaring or buzzing AC line interference that comes and goes at intervals could be caused by arcing contacts in a thermostatically controlled device, a defective doorbell or doorbell transformer inside a nearby residence, or a malfunctioning illuminated advertising display. To determine if the AC line noise interference is being generated within your home turn off the AC power line main circuit breaker and listening on a battery operated radio to see if the noise goes away. If by doing this you determine that an electric motor is a problem, noise from an electric motor can be suppressed by installing a bypass capacitor across the motor leads.

QUESTION: What might be the cause of a loud roaring or buzzing AC line interference that comes and goes at intervals? (E4E10)
ANSWER: All these choices are correct

    • Arcing contacts in a thermostatically controlled device
    • A defective doorbell or doorbell transformer inside a nearby residence
    • A malfunctioning illuminated advertising display

QUESTION: How can radio frequency interference from an AC motor be suppressed? (E4E05)
ANSWER: By installing a bypass capacitor in series with the motor leads

Sometimes your own equipment may be the cause of received noise. Cables in an amateur radio station, for example, can radiate or pick up interference. Common mode currents are the culprits. Common mode current is current that flows equally on all conductors of an unshielded multi-conductor cable. Common mode current on the shield and conductors can can also cause shielded cables to radiate or receive interference. To eliminate this interference, make sure to ground the shield at one end of the cable.

QUESTION: Which of the following can cause shielded cables to radiate or receive interference? (E4E07)
ANSWER: Common-mode currents on the shield and conductors

QUESTION: What current flows equally on all conductors of an unshielded multi-conductor cable? (E4E08)
ANSWER: Common-mode current

The main source of noise in an automobile is the alternator. Conducted and radiated noise caused by an automobile alternator can be suppressed by connecting the radio’s power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads. The capacitors help filter out the noise, and short, direct leads to the battery help prevent noise pickup.

QUESTION: How can conducted and radiated noise caused by an automobile alternator be suppressed? (E4E04)
ANSWER: By connecting the radio’s power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads

Personal computers and other digital devices can also generate noise. One type of electrical interference that might be caused by the operation of a nearby personal computer is the appearance of unstable modulated or unmodulated signals at specific frequencies.

QUESTION: What is one type of electrical interference that might be caused by a nearby personal computer? (E4E06)
ANSWER: The appearance of unstable modulated or unmodulated signals at specific frequencies

Noise can even be generated by the most unlikely things. For example, if you are hearing local AM broadcast band signals on one or more of the MF or HF ham bands it’s possible that nearby corroded metal joints are mixing and re-radiating the broadcast signals.

QUESTION: What could cause local AM broadcast band signals to combine to generate spurious signals in the MF or HF bands? (E4E11)
ANSWER: Nearby corroded metal joints are mixing and re-radiating the broadcast signals

2015 General Class study guide: Section G4C – Interference with consumer electronics, grounding, DSP

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In this section, question G4C11 was changed slightly, and the answer to question G4C08 was changed slightly.

At some point or another, your amateur radio station will interfere with a radio, television set, or telephone. Sometimes this may be your fault, other times it may be the fault of the device. In either case, you should do everything you can to eliminate this interference.

Public-address (PA) systems and telephones are often targets of interference. Distorted speech is heard from an audio device or telephone if there is interference from a nearby single-sideband phone transmitter. (G4C03) On-and-off humming or clicking is the effect that a nearby CW transmitter may have on an audio device or telephone system. (G4C04)

Fortunately, there are many things you can do to reduce or eliminate the interference. For example, a bypass capacitor might be useful in reducing RF interference to audio-frequency devices. (G4C01) You can also use ferrite beads. Placing a ferrite choke around the cable would reduce RF interference caused by common-mode current on an audio cable. (G4C08)

Proper grounding is also important. One good way to avoid unwanted effects of stray RF energy in an amateur station is to connect all equipment grounds together. (G4C07)

Rather than connecting them in a daisy-chain fashion, you should connect them all to a single point. Connect all ground conductors to a single point to avoid a ground loop. (G4C09) If you receive reports of “hum” on your station’s transmitted signal, this could be a symptom of a ground loop somewhere in your station. (G4C10)

A long ground wire will act more like an antenna at high frequencies than it will at DC or low frequencies. As a result, it is important to keep ground connections as short as possible to prevent high-impedance or resonant ground connections.

One effect that can be caused by a resonant ground connection is high RF voltages on the enclosures of station equipment. (G4C06) If you receive an RF burn when touching your equipment while transmitting on an HF band, assuming the equipment is connected to a ground rod, the ground wire has high impedance on that frequency. (G4C05)

A common complaint of amateur radio operators is electrical noise that seems to be on every band. This may be caused by arcing in a power line transformer or at some other connection. Arcing at a poor electrical connection could be a cause of interference covering a wide range of frequencies. (G4C02)

One thing you might do to reduce or eliminate this interference is use a digital signal processor, or DSP. One function of a digital signal processor in an amateur station is to remove noise from received signals. (G4C11)

You can also use DSPs to eliminate interference from amateur radio signals that are close to the frequency you are operating on. A Digital Signal Processor (DSP) filter can perform automatic notching of interfering carriers. (G4C13)

Many modern amateur radio transceivers have built-in DSPs that operate at IF frequencies, or you can purchase speakers designed for communications use that have audio DSPs. An advantage of a receiver DSP IF filter as compared to an analog filter is that a wide range of filter bandwidths and shapes can be created. (G4C12)