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.

T0C12-2018

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

T0C01-2018

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.

T0C07-2018

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

RF burn3.jpg

No Privacy

November 16, 2018November 16, 2018 AF5NP Encode/Encrypt, ID, 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.

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.

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

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

November 14, 2018November 14, 2018 AF5NP RF, 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.

Viewed in 3D animation, it’s not only cool to look at, but may help us understand it a little better. Wave animation The 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).

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

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.

T3B06-2018 For 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.

Wavelength long short.png

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

T3B05-2018

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:

You 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.

Control Operator

November 13, 2018February 27, 2019 AF5NP Control, License, Operator, Station

The control operator is an important concept in ham radio. There are many license exam questions involving the control operator so we want to spend a bit of time on the subject. While legally specific to USA radio amateurs, some of these rules may apply in other countries as well.

A ham radio station control operator is the licensed amateur who is operating a station’s transmit function. Any unlicensed person or even your cat can manipulate station controls with respect to receiving but when it comes to transmission of any signals, there must be a licensed operator in control of the transmitter. This is a fundamental rule of the FCC to regulate ham radio transmissions in the US.

Savvy readers might wonder how this applies to repeaters and more sophisticated stations operated remotely. Control operators are still required for all amateur transmissions. Always a control operator.

With repeaters it is done automatically through a sophisticated repeater controller that follows the rules. However, the repeater station licensee is still responsible and is considered the control operator while using automatic control.

T1E08-2018

With remote control the control operator is simply using some method to indirectly control radio settings, including the transmit function. They are still responsible for transmitter operation even if they are not physically near the radio.

Even if the radio control point is remote from the transmitter, a licensed control operator must be present.

The control operator need not be the one speaking into the mic, using a Morse key or typing a digital message; as long as they are in direct control of the transmitter, someone else can be doing the communicating. That means your friend or relative can do the talking as long as you, the control operator, can intervene if something goes wrong.

Guest under supervision.jpg

When you get an amateur radio grant in the US, you actually receive two licenses: One is your operator license and the other is the station license. Both are associated with your unique call sign.

License example

More commonly, when a ham is transmitting, the operator and station are one and the same, as when KF5ZFD makes a 20m SSB contact in another state from their home location using their own transceiver and antenna.

So why do American hams have two separate licenses? We’ll try to explain here.

Firstly, there are three basic types of FCC-issued Amateur station licenses. Only the familiar operator/primary station license is for individuals. The other two—club and military recreation licenses—are stations intended to be used by licensed individuals.

This means that a ham would use their operator privileges to be a legitimate control operator of a club or military recreation station. In this case the applicable call sign would normally be the station’s, not the operator’s.

Secondly, hams are not restricted to their own station equipment (radio, antenna, accessories). You might visit another ham’s shack and operate their transceiver. In this case, the applicable call sign could be Continue reading →

Radio Frequency (RF)

November 12, 2018November 13, 2018 AF5NP High Frequency (HF), RF, VHF/UHF

Radio signals are sent via radio waves, which are a form of electromagnetic energy or radiation. T3A07-2018

Recall that a radio wave consists of both electric and magnetic fields oscillating at right angles to each other. EM Fields.png

Combining electrical and magnetic gives us the term electromagnetic.

T5C07-2018

Like all waves, radio waves vibrate or oscillate at a specific rate or frequency.

This vibration frequency is normally measured in cycles per second and its units are Hertz. Rates of oscillation in radio work are thousands and millions of Hertz (Hz). With standardized metric prefixes for SI units , this means practical radio frequencies are in kHz, MHz, and GHz.

The common and familiar term RF is short for radio frequency. It’s really an adjective, not a noun. While we may say just RF (“You have a big RF leak, there, Fred”), we really mean radio frequency energy or signals. RF is not a thing in and of itself.

T5C06-2018

So what is a radio frequency , then? They are a large chunk of frequencies in the middle of the electromagnetic spectrum (the range of possible frequencies from 0 to measurably high). Technically radio frequencies start at low audio frequencies and run up to just below infrared light, basically 30Hz-300GHz. Different sources specify other upper/lower boundaries because a more practical range is the low frequency band up through microwaves. However you define it, this range of frequencies is known as the radio spectrum.

RF Spectrum.gif

While hams can use very low frequencies on one end and go up to microwave frequencies at the high end, the more common radio amateur frequencies are in the shortwave, VHF, and UHF range.

We will follow up with detailed posts on the important topics of RF wavelength and amateur radio bands, along with RF safety. Coming soon to Newhams.info; stay tuned.

NewHams.info

Training, information, and encouragement for new amateur radio operators.