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.

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 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

RF burn3.jpg

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.

T1D03-2018.png

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.

G1B06-2015.png

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

T1D11-2018.png

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.

T3B01-2018.png

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).

T3B11-2018.png

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

300m.JPG

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.

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:

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.

Control Operator

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.

T1E01-2018.png

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.

T1E10-2018.png

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

T1E09-2018.png

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)

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

 

T3B03-2018.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.

T5A12-2018.png

ewaves.gifThis vibration frequency is normally measured in cycles per second and its units are Hertz.  T5C05-2018.pngRates 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.

 

License Expiration and Renewal

Relevant to American hams only:  US amateur radio licenses are valid for ten years (10 year grant term).  License term or renewal rules are likely different in other countries.

T1C08-2018

So a newly-licensed ham doesn’t have to worry about renewal for a long time to come. Various organizations will nag you via email, postal mail, and on QRZ when your license expiration is on the horizon (“This license expires soon.  Renew Now!”).  So if you intend to keep your license you should have plenty of warning and opportunity to renew.   You can renew within 90 days of expiration but no sooner.

If, for any reason, you let your license expire, you have a two year grace period during which you may file for reinstatement.

T1C09-2018

However, you may not operate (transmit) whatsoever once your license has expired.

T1C11-2018

Renewal or re-instatement (within the grace period) is simple and straight-forward.  No cost and no re-testing required.  Unlike the old days, you do not need to prove activity for renewal (showing log entries).  Make renewal application on the FCC ULS website.  If you have trouble navigating the process, there are renewal services eager to do the work for you (for a reasonable fee).

Direct renewal via ULS should be very fast.  Your status with new expiration date should show up on the ULS database shortly after processing.  If previously expired, do not transmit until you see a new expiration date a decade away (much like your original license experience).

After the 2 year grace period has passed, the FCC will cancel your license and make it available for reissue. If your license gets canceled, your call sign is lost and you must pass an exam again to get re-licensed. After you have obtained a new license and call sign, you may apply for your old call sign as a vanity call, if it is still available.

Not all new hams are brand new to the game.  Sometimes hams let their license expire due to neglect or lack of interest.  More commonly a ham will find that a career and family interrupt their interest in amateur radio and they just let it slide.  Then years— perhaps decades—later they catch the bug again and want to get back into ham radio.  In some ways they are a new ham because many things have changed (rules&regs, technology).  On the other hand, the basics are familiar so they aren’t totally green.

There is good news for previous holders of General, Advanced or Extra Class licenses.  If you can show Continue reading

Electrical Hazards

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.

Several of these have been used by us previously but in retrospect we should have given the safety topic more airtime, pun intended.  New hams are unlikely to have antenna towers so we don’t plan to discuss tower safety much.  That leaves electrical and RF hazards to cover.

This post will address general electrical hazards and related safety; a future post will focus on RF hazards.

Radios and accessories are electrical devices so let’s start with the most obvious hazard: electric shock, which is caused by current flowing through a human body.  Current is useful in electronics but harmful when flowing through a person.  Current can disrupt heart and lung function at even low levels.  It can also cause unwanted muscle movement, or prevent it (can’t let go).  At higher levels, electric current will damage skin and internal organs.

T0A02-2018

There are many factors in electric shock and there are other electrical hazards.  But this is a big one and you should avoid touching live circuits.

Fire is another electrical hazard.  When too much current flows in conductors, the wires can get very hot and ignite combustible material.  In fact, the US National Electrical Code is actually a document of the National Fire Protection Association (NFPA), not a government agency.

To limit the risk of fire and other damage, every power circuit needs some form of  protection.  Fuses are quite common; their internal metal melts at a pre-determined current to disconnect power.

T0A04-2018

Also, a smaller (amp rating) fuse can safely be inserted in a protective circuit but one should never put in a larger one.  A fuse is sized to the circuit requirements and wiring  is sized to the fuse.  So a higher-ampacity fuse will not properly protect the wires or the circuit and serious overheating may occur in both AC and DC power circuits.

T0A05-2018

In addition to one-time use fuses, circuit breakers are another popular form of circuit protection; these may be reset and are often used as an on/off switch.

T0A08-2018

While fuses and circuit breakers do not directly provide shock protection, they may do so Continue reading