GMRS and Amateur Radio Basic 101

Lesson 1

What is the difference between a “channel” and a “frequency?” 

Frequency is expressed in hertz (hz), or megahertz (mhz) for 1,000,000 hertz.

To receive a signal that is transmitted, both radios must be on the same frequency.  The FM broadcast radio in your car is a good example.  If you want to listen to a radio station that broadcasts on 105.5 Mhz, then you tune to that frequency.  If you do it a lot, then you might use the preset, so you only have to push one button. Essentially, you have programmed a “channel” in your radio.  On your television, the manufacturer has programmed the “channels” for you.  On your cable TV box, the cable company programs and reprograms your channels on the box through the cable.  (Don’t you just love it when you like to watch a program on a cable channel, then you turn it on the next day to find its now the “golf channel.”)

The “FRS (Family Radio Service)” walkie-talkies you usually see for sale in Home Depot or Walmart have pre-programmed channels.  These are short range only.  (2-4 miles).  They don’t require a license, AS LONG AS they are used within the rules. They will not have the ability to attach an external antenna.

We can program ham radios and most “GMRS” radios from the keyboard or with a computer.  These can be hand held radios, mobile radios, or base station radios.  In other words, its like setting up “speed dial” on your telephone.

Radios that can transmit on Ham AND GMRS or FRS (on the same radio) are/were usually sold on the internet. The FCC has stopped importation of these to some extent.

Why do we need two different frequencies on one channel?

To use a REPEATER we have to transmit on one frequency and listen on another aka “duplex”.  This is called an offset.  For UHF, its traditionally 5 Mhz.  This is because most repeaters must transmit and receive AT THE SAME TIME.  Frequency separation is necessary to prevent feedback and burning out the receiver.  The good news is that ham radios have this offset preset in the menu for us, so it’s automatic.  Our programming software usually fills in that blank for us.  If we program a channel from the buttons on the radio, we usually don’t have to worry with it.  We don’t need an offset to talk “simplex,” meaning direct (no repeater).  With GMRS radios, this may be pre-set or may require you to go into a menu to set. 

Since the Chinese have been marketing radios that may be programmed for ham or GMRS, much of it is not automatic.  These radios are more difficult to set up and there are legal issues.   UHF Ham (only) radios usually can be modified for GMRS, but there are still legal issues.  (Kinda like the CB radio issues.)  Newer Chinese radios (Baofeng) are less likely to work on both, depending on the company importing them.  U.S. Customs apparently has cracked down on the larger importers.  You may hear that this is all in the “no-one-cares” category, but when I fly, I would not carry a Chinese radio through TSA or Customs.  The Japanese brands do not have import issues.  Baofeng is becoming more compliant with FCC rules. 

Lesson 2

What is “tone” with respect to ham or GMRS radio?

On most ham, GMRS, commercial, or public safety repeaters a subaudible tone must be transmitted with the signal to trigger the repeater.  There are specific tones (outside of the ability to hear) that can be programmed into the channel you enter the repeater frequencies in.  When you see the term “memory” in a manual or radio menu, they are referring to the frequencies, tone, etc. that you have programmed into that “channel.”

The purpose of the tones is to keep interference from keying up the repeater.  (Some repeaters are just two radios tied together with special circuits.)

A company called RT Systems sells software and cables for programming MOST ham and some GMRS radios.  It’s always best to learn how to program from the keypad first, but if you reprogram numerous channels or do it often, the software is the way to go.  On a computer, the software opens something like a spreadsheet to load the data into. 

Remember you can always listen by just entering the listed frequency.  You don’t need to deal with the offset or tone for that. 

Other types of tones can be used, such as digital tones, or tones for the receive AND transmit, but that’s when your further along. 

If you hear a constant noise instead of people talking on a frequency, that’s usually because they are in a digital mode.  You won’t be able to listen on regular FM.  Our local repeaters automatically work on either, but if someone enters the conversation in regular FM, everything will switch to FM automatically.  In some areas you may find repeaters that are NOT automatic and only operate digital.  Only ham repeaters do this.  GMRS repeaters can not operate in digital modes.  There are no FRS repeaters, however both systems share a few frequencies. 

There is a simplex repeater in the area on VHF at 147.420, but you will likely only hear it south of SR44.  You will hear world-wide radio traffic on it.  It is fed into the system from an internet connection to the repeater. 

You CAN listen in on 443.375 Mhz right now.  The local ARES UHF repeater is also connected.  Once you get a ham license, you will be able to transmit on it.  The British Girl Scouts were connected from Wales this morning.  They were talking to Bud (W4YEE) in Beverly Hills. 

Internet connections are fed into some repeaters from servers that are called “Reflectors.”  443.375 is on the “East Coast Reflector.” The connection system between radio and internet is called “Allstar” if it has the ability to mix different modes.

Lesson 3

AMATEUR RADIO FREQUENCY CHARTS

To learn about the frequency and modes of operation for each license class, we typically refer to one of the frequency charts published by the ARRL on their website at: https://www.arrl.org/graphical-frequency-allocations. The charts can be downloaded from the webpage in various formats to suit your needs. You will want to print one of these for your radio area. We typically memorize some of it by using it so often. There is usually a test question or two related to frequency information on the charts.

FREQUENCY vs. WAVE LENGTH

Since this section involves metric units of measure, you might want to take a quick look at this quick reference on metric measures.

When talking radios, we use the terms frequency and wavelength often. The terms are NOT the same, but they are mathematically related. Radio waves are electromagnetic and radiate back and forth between negative and positive voltage, just like the power you get from an electrical outlet at home (alternating current or “A/C”). This type of wave form is a sinusoidal wave, or sinusoid (symbol: ∿). We usually just call it a “sine wave,” for short. (Sine is also a trigonometry function. They are related, but you won’t need that information for this license.)

When we graph a sine wave it looks like an “S” on its side.

Frequency is the number of waves in one second.

In radio, we use the term megahertz (Mhz) or kilohertz (Khz) to describe a radio frequency. It means one million or one thousand hertz. (Hertz was the name of the scientist that studied this principle.) Hertz may also be called cycles. Old radios may have “Mc” or “Kc” on the dial.

Wavelength is the measure of the length of the wave in meters. (Everything is metric in science.) To determine wavelength from the frequency, we use the formula:

300 / frequency in mhz = wavelength in meters

For instance, our local VHF repeater transmits on 146.955 Mhz.

To convert to wavelength: 300 /146.955 = 2.04144126 We just round this off to 2.

In amateur radio we call our VHF band “2 meter.” It ranges from 144-148 Mhz. The amateur band in the 420-450 Mhz range works out to about .7 meters. Since .7 meters equals 70 centimeters we usually call it the 70 cm band for convenience. This is very close to the GMRS band. When describing a particular band, we usually calculate from the middle frequency in the band, then round off.

By the way, wavelength tells us how long our antennas need to be to work properly. (There is a simple formula for this using inches.)

MODES

When we refer to “mode” in radio, we are referring to AM or FM, and others, much like AM and FM on your car stereo. AM is the acronym for amplitude modulation and FM is the acronym for frequency modulation. The Amateur Radio Technician license allows the use of amateur radio bands in the VHF (144-148 Mhz) and UHF 420-450 Mhz range). FM is the usual mode for VHF and UHF. FM is the only allowable mode for GMRS.

Please watch this video: https://www.youtube.com/watch?v=QEubAxBfqKU

Other modes a Technician may use include digital, continuous wave (cw), or single sideband (SSB) on ham radio. AM is still used but rarely. There are AM groups that meet on the air in the shortwave bands weekly.

The CW mode is the first mode ever developed for telegraph and early radio. You may know it as “morse code.” Turn on your sound, and CLICK FOR CW MESSAGE. There are frequencies in most of the authorized amateur radio bands reserved for cw use. Morse code is no longer required for any level of amateur license, but many still enjoy using it. It is advantageous for low power and weak signal use. It is popular for radio contesting in the shortwave bands.

There are a variety of digital modes. Some are proprietary and are found as an option on certain brands and models of radios. Digital modes work like a computer or fax machine - just a combination of off-and-on at really high speed. CW is very similar, but can be decoded by just listening. Email and low-resolution photos can be sent over radio using digital formats. Live television signal may also be transmitted, however is more of a novelty.

Single sideband (SSB) is the predominant mode used for voice communications over shortwave bands (3-30 Mhz). It is sometimes used on VHF or UHF when band conditions meet certain criteria. SSB is like using half of an AM signal. Its either lower sideband or upper sideband. It draws less power than AM, which helps save battery power when portable. A smaller portion of the band is used, so more operators can operate within the band. There is less noise on SSB than am, but more than FM.

Lesson 4

How many miles can I transmit with my radio? Or What’s my range?

Well……... this is going to take a while to explain.

Radio frequencies are usually grouped in “bands.” This is just a convenient way of grouping frequencies for regulatory, technical, and practical reasons. We will refer to “bands” a lot from now on. Amateur Radio (aka “Ham”)

When we talk about most radio bands, we find the frequency range within a particular band has similar characteristics with respect to distance, penetration of objects, and propagation. Ok, here is a new term – propagation. Some radio signals will refract when they enter the ionosphere. Refraction is not the same as reflection, but the end result is much the same. This is often called “signal bounce.” The degree to which this works varies by the frequency, time of day, and space conditions. Radiation from space, like sun light, alters the degree of ionization of various levels of the atmosphere. As a result, some frequencies refract better at night than in the daytime and vice versa. This is why CB radio is so noisy most of the time, especially at night. If you are old enough, you may remember listening to the Grand Ole Opry in Nashville on AM broadcast radio at night. “Shortwave” radio depends on propagation. “Shortwave” covers frequencies below 30 mhz to one mhz. Because of propagation, we can usually communicate around North America during the daytime in the 14.1-14.4 mhz range. It fades a little after sundown most of the time, and 3.8 – 4 mhz begins to propagate until daylight and early morning. Lower frequencies tend to curve with the earth a little. Since we may be communicating beyond our time zone, it may be good here, but not there, or vice versa. Like Jimmy Buffett said, “its 5:00 somewhere.”

As it turns out, radio frequencies above 30 megahertz don’t refract often. The higher the frequency, the less likely it will ever refract, however during foggy conditions we occasionally experience temporary “tropospheric ducting” on VHF or even UHF. (Think Star Trek “worm holes.”)

Ham radio uses VHF (144 -148 mhz) and UHF (420 - 450 mhz) for local use. FRS operates around 462 mhz and GMRS operates around 462 and 467 mhz. The Marine VHF band is 156 -174 mhz. VHF has been known to travel hundreds of miles. UHF may reach 200 miles with normal antennas. VHF and frequencies above are considered pretty much “line-of-sight” because they rarely refract or reflect. As a result of the line-of-sight limitation, the height of your antenna will usually determine your maximum range for VHF and especially UHF. The line-of-sight will vary a bit from the radio signal path due to various factors. Lower frequencies tend to curve a little with the earth, but higher frequencies curve less.

Higher frequencies will usually penetrate objects and materials better than low frequencies. For this reason, VHF works well outside and to a lesser degree inside homes and buildings. Buildings will block VHF signal depending on the materials. Density, molecular structure, and moisture content are factors. Metal roofs are difficult to penetrate, period. Hotel windows and glass doors are often tinted with metallic substances that block signal to some degree. More power output usually helps. UHF penetrates buildings much better, but is still limited. This is particularly an issue when using hand held radios. We measure output power in “watts.” For these reasons, you will find more UHF repeaters in cities with high-rise buildings.

A “base station” or “mobile” radio will usually have an external antenna, so it will do better and need less power. The higher the antenna, the more range you will have. This is why radio repeaters are usually mounted as high as we can get them. In Florida an antenna at 300 feet on the UHF band can usually cover a 40-mile radius with 50 watts of power output. The ground elevation is part of that height. It is usually not possible to penetrate hills and mountains. Trees affect VHF depending upon their moisture content. When there are no obstacles or hills UHF will travel a little further on lower power outputs than VHF.

Since the Technician radio license enables a new ham to operate on VHF and UHF, a handheld radio is often a new ham’s first radio. You can usually expect a four-mile range at best on flat ground between two hand held radios. Being on top of a hill will extend that. Plugging into an external antenna will help a lot. Since hand held radios rarely emit more than five watts, a mobile radio is much more useful. They are usually 50-100 watts and an antenna on a vehicle is a better radiator of signal. “Rubber ducky” antennas don’t have the benefits of a good ground or “counterpoise”. Despite the advantages of installing a radio in your vehicle, the range can be expected to be only four to 10 miles on flat ground without major obstacles. When contacting a base station radio or repeater, this range extends dramatically. Just FYI, you can buy a mobile radio and hook it to a power supply to use it for a base station. A VHF or UHF handheld can transmit about 200 miles to another handheld in an aircraft by a window that is flying at or over 15,000 feet. (Yep, I’ve done it.) The curvature of the earth becomes a factor then.

Try this online calculator: https://www.everythingrf.com/rf-calculators/line-of-sight-calculator. Tip: A kilometer (km) is about .6 miles. Get used to metric!

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