Software Defined Radio (SDR)

January 23, 2019January 23, 2019 AF5NP Software Defined Radio (SDR)

While not really a topic important to new hams, Software Defined Radio (SDR) crops up often in amateur radio publications and advertising so we should at least introduce the idea here.

As its name suggests, SDR involves software working in radio equipment. More than just being used for operator interface and general control, SDR software specifically replaces the functions of signal processing hardware employed by traditional radio circuits.

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SDR greatly simplifies radio circuitry by replacing the functions of hardware oscillators, mixers, filters, modulators/demodulators, and detectors with software. Since software is easily changed this also means that radio functionality may easily be improved or enhanced, or allow for new modes, protocols, and interfaces to other devices by reconfiguration or reprogramming.

SDR may be used on radio transmitters but the most common implementation is with receivers. Most of the popular and available SDR products are receivers and most employ direct digital conversion techniques.

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One of the more defining characteristics of SDR is the user interface (integrated or PC display) waterfall display and menu-driven controls interface.

hdsdr

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There are various SDR interfaces out there, many (most?) are free applications. These will typically have a waterfall display showing the entire receiver passband, band/frequency controls, filtering and other features (volume, AGC, noise, mode), and display controls/customization, along with recording and playback capability.

Current SDR use in amateur radio is typically for the HF bands; stand-alone modules or dongles running on PCs are commonly found and complete transceivers are quite popular although more expensive than traditional HF rigs (see references below). As of this writing, the author is unaware of any widely-available VHF/UHF FM mobile or handheld Continue reading →

Radio Brands

January 8, 2019January 8, 2019 AF5NP Brand/Manufacturer, Quality, Radio, Reliability, Repair

A ham new or old has many choices for radios and radio gear available. We don’t want to tell radio amateurs what to buy or not to buy but will give some guidance here.

The modern natural progression is to start with a handheld VHF /UHF transceiver, then a mobile VHF /UHF unit, then a base HF rig. These have different characteristics which must be considered so the first question is what type of radio are we buying?

Beyond the basic type there are several factors in selecting a radio brand. It usually comes down to the buyer’s top three or four priorities from this list of characteristics:

Functionality
Features
Performance
Quality
Reliability
Durability
Ease of use/programmability
Memory capacity
Familiarity
Style/Appearance
Portability
Price

Unless you are looking for a specialty radio (i.e., low-power portable CW operation), size isn’t much of a factor these days as within a general family all radios have similar weights and dimensions.

From this list the top consideration should be functionality (what it does, exactly) as that is most relevant. Say you want a dual-band FM HT to work the local repeaters or for EmComm deployment. You have more than a dozen choices available.

Refining further by features for things like APRS, power levels, battery type, weather resistance, and whatnot will narrow your selection but you still have many to choose from. At this point you’re likely to think about price and here is where things get fuzzy. You could choose the nice name brand $350 radio but there’s one that does mostly the same thing for $50.

Sounds like a slam dunk decision to go with the cheaper one, but you should carefully consider this. Beyond functionality and features, important characteristics suffer. With that low price you get questionable performance, low quality, poor reliability, and lack of durability, not to mention fewer features. As the saying goes, you get what you pay for.

Now that doesn’t mean you should never buy a cheap radio, but you should really think about doing so. Some HTs are so inexpensive they can be considered disposable. If you lose or break one, you’re out only $30-50. This may be a good candidate for backup or one you might take boating or on a camping trip or loan to a prospective ham to listen on. You can find favorable reviews on some of these cheap radios (mainly HTs and mobile rigs). But you will also find many negative reviews on the same radios, mainly for reliability and durability. Some of the cheap Chinese radios also have poor RF characteristics, lack FCC certification, and are not strictly legal for use in the USA. So it’s a crap shoot if you do want to buy a cheap radio.

There are three well-known name brands that have reputations for high quality and reliability: Icom, Kenwood, and Yaesu for hand-held, mobile and base station radio equipment. These will cost more but will give many years of service and are worth repairing should one fail or be broken. All originate in Japan but have strong presence in the USA and other countries. American companies Elecraft and FlexRadio make awesome premium HF rigs but they are not competing for hand-helds or mobile units.

Alinco was another Japanese manufacturer with a good reputation, arguably up there with the Big 3 but is now developed and built in China.

Pre-owned equipment will be less expensive than new, of course, but the price between used reputable brands vs unreputable will be proportional. With used radios you also can find older HF brands with excellent reputations.

The author’s own sad experience with an off-brand mobile radio has led him to this topic and a determination to never again buy a cheap non-disposable radio. He purchased a Continue reading →

HT Antenna Improvement

December 11, 2018December 11, 2018 AF5NP Antenna, Counterpoise, HT (Handheld Transceiver), J-Pole, Rat Tail, Slim Jim, VHF/UHF

The handheld transceiver (HT) is likely a new ham’s first radio. This VHF/UHF rig is relatively inexpensive, compact and fairly useful for local communication via repeater or simplex operation.

Unfortunately, HT performance is typically limited by its low power and cheap factory antenna.

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There are three easy ways to improve the HT antenna. These ideas are from our post on Understanding Antennas but we wanted to elaborate a bit on them here.

The first improvement is to get a 2m ¼-wave or 5/8-wave whip antenna.

This 2m ¼-wave whip is much longer (~19″) compared to the factory antenna but gives dramatically better performance (roughly equivalent of 5x power):

QW whip

This telescoping 5/8-wave whip should (in theory) perform better than the ¼-wave monopole (shown with 5/8-wave mobile whip):

5_8 Whip

These two antennas can be purchased new in the $20-30 range; well worth the money.

While the antenna can be improved with a longer whip, vertical monopole performance is also limited by the HT’s indirect ground plane.

The counterpoise that makes the vertical monopole behave like a λ/2 dipole on a HT is the operator’s body. It is capacitively coupled to the ham’s body through the plastic case and metal shell around the RF circuitry.

This indirect counterpoise coupling is not only weak but also highly variable and unpredictable.

The good news is that we can improve the counterpoise simply by adding a wire to the HT antenna connection.

By connecting a ¼-wave wire (~19” for 146MHz) to the antenna connector outer terminal, we create a physical counterpoise in place of the indirect ground plane through the operator’s body.

This gives superior performance under difficult conditions and is easy to do.

These physical counterpoise wires are known as rat tails or tiger tails due to their appearance.

Rat tail counterpoise installation is quick and easy. Simply unscrew the antenna, slip the rat tail over the connector and re-attach the antenna

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tiger tail2

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The rat tail can simply hang down in a gentle arc where it won’t be much in the way of anything. Even better, you can hold the wire out in the direction of communication. Gain/directivity is achieved Continue reading →

What You Need to Know About Electrolytic Capacitors

December 4, 2018December 4, 2018 AF5NP Capacitor, Component, Electrolytic, Repair, Troubleshoot

Capacitors are a fundamental electronic component and their property of capacitance in Farads (F) are a core part of radio circuitry.

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The basic capacitor is a pair of metal plates separated by some form of dielectric insulation.

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Electrolytic capacitors are special because they have a lot of capacitance—hundreds or thousands of microfarads (µF)—in a relatively small package.

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Most big electrolytic caps are in the radial package where both leads are on one side. The axial package with one lead on each end of the cylinder are sometimes used. See axial vs radial.

Aluminum electrolytic capacitors provide the highest values while remaining relatively inexpensive so are commonly encountered in radio and electronics. This is possible because of wet chemistry; specifically, an electrolyte solution as part of the dielectric layer between metal plates. Aluminum foil is the primary conductive surface and the electrolyte is part of the separating insulator.

Aluminum electrolytic capacitors are frequently used in power supply circuits such as shown below, and are found in most every type of electronics:

Figure T-2

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OK, so this is wet chemistry but a dry topic. Why are we boring you with all this?

There is a practical point here for those of you who are handy or brave enough to tackle your own electronics repair; hams tend to be a DIY group. Be advised that many functional problems in all sorts of electronics—not just radios—can be attributed to failed aluminum electrolytic capacitors. We hope to encourage you to fix an expensive piece of equipment, not just toss it or pay someone to repair it for you.

Usually an easy fix with just two component leads to un-solder and then re-soldering the replacement. Diagnosis Continue reading →

Indirect RF Hazards

November 27, 2018November 27, 2018 AF5NP Antenna, Controlled, Duty Cycle, Environment, Evaluation, Exposure, Hazard, High Frequency (HF), Ionizing, Limits, MPE, Protection, Radiation, RF, Safety, SAR, Uncontrolled, VHF/UHF

Part 3 on Safety

Safety is an important topic in ham radio. There are 11 questions on electrical hazards in the USA Technician class license exam pool, 13 questions on tower safety and associated grounding, and 13 questions on radio frequency (RF) hazards.

Part 1 on general electrical hazards and Part 2 on contact RF hazards were posted previously. This post will address indirect RF hazards. In case you are not familiar with the specifics of RF energy, refer to our post on the subject.

Here we are concerned about non-contact RF energy. A long and involved topic (sorry about that) but full of useful detail.

While it involves radiation, RF energy radiates at lower wavelengths where it is least hazardous.

radiation spectrum.JPG

From the electromagnetic spectrum diagram above we see that radio waves are on the low end of energy levels. As the frequency increases (wavelengths decrease) the energy in electron volts increases exponentially. Energy above 250eV (or so) is ionizing, which in addition to radiation burns can cause cell damage and mutations, leading to cancer and other maladies, as would radioactive material.

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Fortunately for hams, all radio frequencies are well below the ionizing radiation energy levels.

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Ham radio operators are radio active, not radioactive. 🙂 Amateur radio active Now just because RF radiation is non-ionizing doesn’t mean it is completely safe. Besides the direct contact hazard, exposure to radio frequency energy may cause localized tissue heating, particularly in the eyes and male reproductive area (here’s where a lady ham has an advantage, hihi). Non-thermal effects of RF radiation are being studied constantly because, while compelling, they are somewhat ambiguous and unproven.

Because RF energy has this radiated exposure risk, rules and regulations have arisen to protect people from such hazards. In the USA this is done at the federal level by both the FCC (radio communications) and OSHA (occupational). There are also guidelines for RF radiation published by the ARRL and the IEEE. Internationally, most countries apart from the US have similar guidelines, as does the World Health Organization (WHO). References to some of these are given at the end of this presentation.

Specific to US radio amateurs, the FCC instituted RF field exposure limits called Maximum Permissible Exposure (MPE). Continue reading →

Silent Key (SK)

November 23, 2018November 21, 2018 AF5NP Ham-Speak, Silent Key (SK)

The term SK is another bit of ham-speak that is not obvious to new or prospective radio amateurs and you should know what it means.

While widely used in ham circles, SK has two differing meanings. Specific to CW work, SK is a Morse code procedural signal (prosign) for indicating a final transmission in a message or QSO.

More generally, SK means silent key, a term of respect for a deceased ham. It’s a classy way to denote the loss of a member from the radio amateur community. Hams will sometimes give tribute to SKs in their biographies as influencers or Elmers.

Silent Key is a dignified term going back to wired telegraphy, adopted in the early days of ham radio when only Morse code was used to honor a CW operator whose key will not be heard again. This tradition has carried over into modern times when voice, video and data have been added to the amateur radio repertoire. Considering the prosign SK as “end of transmission,” the double meaning of SK is very fitting.

The ARRL monthly magazine QST prints a list of Silent Keys reported to them.

QST SK

QRZ also has a page dedicated to listing Silent Keys….

QRZ SK

….and they will also note such on Continue reading →

Contact RF Hazards

November 20, 2018November 19, 2018 AF5NP Hazard, Protection, RF, Safety, Skin Effect

Part 2 on Safety

Part 1 on general electrical hazards was posted previously. This post will address contact RF hazards. In case you are not familiar with the specifics of RF energy, refer to our post on the subject. A future post will cover the broad context of non-contact or indirect RF (radiation) safety. Both direct and indirect RF exposure will heat living tissue.

RF burn2

Here we are concerned about direct contact with a RF signal of significant energy. This might happen if a person or animal touches a conductor carrying RF energy. This most likely happens when someone touches an antenna element while the radio is transmitting. It’s painful…..as in, full of pain.

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Another risk of RF contact is while working on live transmitter equipment or an antenna connector. It’s not hard to accidentally key the mic with your hands inside a transmitter enclosure or while touching an un-mated RF connector.

Human skin contact with live RF conductors is a painful experience above very low power levels. What makes it painful is that RF energy heats and damages tissue beneath the outer layer of skin, resulting in 2^nd and 3^rd degree burns. Not normally superficial, RF burns heal slowly.

RF BURN

Without going into physiological details, we will simply quote one person’s testimony: “For the first half-hour or so, all I could see was a tiny dot on my fingertip, and I didn’t think much of it. As the day went on, it hurt more and more, and by the end of the day there was a big, deep, dark blister that covered my entire fingertip and hurt like hell. It took weeks to heal.” There are some good references to RF burns at the end of this post, including a number of personal experiences.

There are a several factors involved in RF burns: Power level (available energy), contact surface area (more is better) , grounding/return contact (less is better) and radio frequency (the body absorbs more energy at certain frequencies).

How much power is needed to create a RF burn? Again, it varies. There are reports of people getting fingertip burns by touching the top of the antenna connector on a relatively low-power handheld VHF transceiver (5W) and keying the PTT button with no antenna screwed in. Obviously, a 100W HF transmitter can do much more damage than this. You don’t need to touch a 50kW AM broadcast antenna to get a nasty RF burn.

Treatment of RF burns are just like any other type– run cold water over it and/or ice it and seek medical attention. Avoidance is the best defense. Of course, most RF burns are unintentional so the best we can do is make you aware. Stay safe!

Direct RF burns cause more immediate tissue damage than indirect radiation but there is a hazard with both; be looking for a future posting in indirect RF hazards.

RF burn references

Ham radio school

Forum with several detailed experiences reported

eHam My Very First RF Burn! interesting with experiences of many hams

EEVblog forum how does RF feel/taste? how about rf injury?

Compilation of various research studies

Biological effects of RF energy

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