HT Antenna Improvement

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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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

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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Electrolytic Cap
Electrolytic capacitor assortment

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.

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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

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.

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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 activeNow 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)

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

Part 2 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 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.

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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 2nd and 3rd 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

Reddit

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No Privacy

New or prospective hams should know that there is no expectation of privacy in amateur radio.  Anything that you communicate legally can be received by other people.

Ham radio involves transmitting intelligence (voice, Morse code, text data, pictures) to be received and understood somewhere else.  By its nature when you transmit a RF signal it goes out into the world (maybe beyond) where anybody with the proper equipment can receive it.

If you are transmitting on a repeater or other well-used frequency someone else is likely to copy you.    However, the chances of someone monitoring a random frequency and mode is rather slim.  People scanning repeaters or tuning around the HF bands may listen but if what they hear isn’t interesting they may move on.  So the likelihood of your QSO being listened to depends on frequency, mode, and content.  Basically, others can listen but this doesn’t necessarily mean that they are doing so.

Hams cannot legally encrypt or disguise their messages for privacy as this violates rules against secretive transmissions.

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The two reasonable exceptions are when sending control commands to orbiting amateur satellite repeaters and when operating a hobby model such as a RC airplane.

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Digital (RTTY, PSK, JT, FT, Olivia and the like) and video (ATV, SSTV) signals cannot be interpreted by ear so there is some privacy from the general public listening in.  But anyone with the right equipment can decode these and follow along.  While these modes are technically encoded, they are not secretive because they are commonly used.

You also cannot secure privacy via anonymity.  Stations at both ends of a message must legally identify themselves

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Of course, if someone really wants to be secretive and violate US amateur radio Part 97 rules by encrypting their transmissions or not identifying, that is a possibility.  We hope that all hams choose to play it straight and follow the rules, in which case anything that you say over the air can be picked up.

Our best advice is to not worry about privacy.  Don’t say anything over the air that you don’t want others to hear.  If you must do so, use a different means of communication.

Wavelength

We recently discussed radio frequency (RF) signals and radio waves.  Now let’s review the related concept of wavelength because it is often used in ham radio.

At any frequency it takes a certain amount of time for a wave to complete one cycle.  A cycle is any repeating feature of the waveform.  Radio waves have sinusoidal form.

Wavelength cycles

Because the wave moves over time, it travels a certain distance in any given period.

Wavelength distance

Wavelength is the distance a wave travels in one complete cycle.  We measure this in meters.

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Viewed in 3D animation, it’s not only cool to look at, but may help us understand it a little better.Wave animationThe red and blue sine waves are the electric and magnetic fields oscillating at right angles to each other at the radio frequency.  The constant wavelength (λ) follows E field peaks between the X and Z axes. The radio wave is moving along the Y axis (lower right).

Radio waves are typically oscillating millions of times per second (MHz).  They are traveling near the speed of light (300 million meters per second).

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The time it takes for a radio wave to complete one cycle equals the speed of light (approximately) divided by the radio frequency:

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Simplifying the math shows us that to calculate wavelength, we simply divide 300 by the frequency in MHz.  The millions (Megas) cancel each other out.  The resultant wavelength is in meters.

T3B06-2018For the center of one popular HF band the wavelength would be:  300/14.2=21m  See how it works?

The wavelength at the center of our most common VHF radio band would be:  300/146=2.05m   

Logically, higher frequencies complete one cycle in less time than lower frequencies.

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This means that the wavelength of higher frequencies is shorter than that of lower frequencies.  Frequency and wavelength are inversely proportional.

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Wavelength is simply an inverted way of thinking about radio frequency; they are mathematically related.

It helps to visualize the two overlaid on a RF spectrum chart:

RF-spectrum-RF-Page.jpgYou can see how the yellow wavelength values above the blue frequencies increase in opposite directions.  Note also how the values line up in 1/10/100s and 3/30/300s per the speed of light relationship.

Wavelength becomes practical when dealing with antennas where element lengths need to be some fraction of a particular RF wavelength.

Wavelength is also the most common descriptor of radio frequency bands.  We will follow up with this in a future topic.

Wavelength is not terribly mystifying but it isn’t very obvious either.  Hopefully this gives you a better grasp of this important subject.


A fairly technical yet easily understood video relating frequency, wavelength and the speed of light is worth watching here.