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.

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.

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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.

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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.

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

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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.

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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.

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 license 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

 

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Combining electrical and magnetic gives us the term electromagnetic.

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

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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.

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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.

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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.

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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.

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

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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.

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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.

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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.

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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.

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

Repeater Reverse

If you aren’t familiar with VHF/UHF repeater operation, now is a good time to review it here.  Repeaters are frequently used for chatting with local hams, regular nets, and EmComm use.

An occasional problem with repeater operation is when a weak transmitter doesn’t have enough power to keep the repeater’s squelch open.  That is, you can tell someone is there but hear little or no signal.  Could be that the transmitter is in a sheltered location, doesn’t have a good antenna, or using too little power.

For whatever reason, they can’t break through with a strong enough signal to be heard.  If you suspect this is happening, you can try listening to them directly instead of through the repeater.  It’s possible that you are closer to the weak transmitter than the repeater is.

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Many hand-held radios (HTs) and mobile VHF/UHF transceivers support this with a repeater reverse function, typically by pushing a button on the radio.

Kenwood Reverse

Recall that a repeater re-transmits what it hears on a different frequency.  The difference in transmit and receive frequencies is called repeater offset and this minimal difference is needed to allow for sharp filtering between them so that the strong transmit signal doesn’t damage sensitive receiver circuitry.

By selecting reverse on a transceiver you then listen to the repeater input frequency instead of its output.  In this manner you can get the weak transmitter’s true signal strength and quality, not what the repeater re-transmits.  This assumes that you are receiving better than the repeater, which is a possibility but not a certainty.

Useful when you want to see if a weak signal Continue reading

Dummy Load

Radio amateurs should be familiar with the term dummy load, which is a RF-friendly substitute for an antenna when testing a transmitter or piece of equipment such as a Watt meter.

Dummy1   Dummy2   Dummy3

A dummy load is somewhat generic, also having industrial and commercial uses.  As applied in ham radio, it electrically simulates an antenna to allow a transmitter to be tested without radiating radio waves, typically at 50Ω to match transmitter output impedance.

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Dummy loads are rather simple—  just a big resistor and some way to dissipate heat, all in a package that must be non-reactive, meaning it provides insignificant capacitance and inductance.

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Why must a dummy load be non-inductive?  Because of impedance (practically speaking, AC resistance), which increases with frequency based on the formula of inductive reactance XL=2πfL.

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Most common power resistors are wire-wound, which have significant inductance.  So RF dummy loads must use resistors with little or no inductance.

As an example, this four-resistor series combination using common Dale metal-clad resistors measures 49.4Ω at 0Hz (DC).  Sounds like a perfect dummy load, right?

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Unfortunately  it also has Continue reading