Guest Article by “Minerjim”
Ham radio can provide a reliable independent means of communications in a survival situation. Hams presently provide communications services in emergencies around the globe, usually on a volunteer basis.
While I think many people who live the “prepper lifestyle” have bought radio equipment, I suspect that they have not learned how to use it fully, or have not really investigated all of Ham radio’s potential. It’s a BIG field to investigate!!!
I’ll attempt to outline the basics of ham radio frequencies, their attributes and downsides, and hopefully arouse some to investigate radio communications further.
Why talk about Ham (amateur radio operator) frequencies only?? Why not talk about all radio frequencies???? The main reason is that certain frequencies are blocked out for use by Hams, to practice with and learn about. This has been going on for about 100 years.
There has been lots of data and information written about these frequencies that is available for everyone to pick up and learn freely. Actually, you will find many Hams will love to talk your ear off if you ask them questions about radio. So lets look at what these frequencies are and who has access to them.
Ultra-High Frequency (UHF)
300 Mhz – 3 Gigahertz
When Hams talk about UHF, they are talking about frequencies in the range of 300Mhz to 3Gigahertz (microwave). This includes the ham bands 70 centimeters and microwave communications as well as FRS/GMRS frequencies. This frequency can be utilized by hand held “Handi-Talkies”, like the Bao Feng, and others.
Communications are mostly done “line-of-sight” and “ground wave” with voice (noted as SSB by Hams) dominating. This means if you can see it, close by, you will likely be able to communicate with it. However, buildings, trees, terrain will interfere with your signal, and communication will become “iffy”.
There is no “skywave” communication with UHF, meaning that you can’t bounce UHF radio signals off the ionosphere to communicate over long distances like you can with other frequencies (“skip” in Ham talk) . If you plan on using these frequencies, expect ‘line of sight’ short range communication only.
If you are lucky enough to have “Repeaters” in your area, this will extend your range a bit. (More on this later). UHF frequencies are open to all Hams with a minimum of the very easily obtained Technician’s license.
(Note here, there are other forms of communication used with Ham radio including data, and computer driven text modes).
Very High Frequency (VHF)
30 Mhz – 300 Mhz
VHF are the frequencies in the range of 30 MHz to 300 MHz. This includes the ham bands 6, 2, 1.25 meters, VHF television and FM Broadcast bands.
Here again the best communications are “line-of-sight” and “ground wave” (out to about 25 miles in good conditions). But radio signals in these frequencies are more robust and forgiving of obstacles than UHF. So communications out to 100 miles or more on flat terrain are sometimes possible, but not always reliable.
Also as mentioned above in the UHF frequencies, if you are lucky enough to have VHF repeaters in your area, your communication distances can be extended a lot farther. Here again, there is no real “skywave” communication of bouncing signals off the atmosphere (Skip) for long distance communications.
VHF frequencies are open to all Hams with a minimum of the Technician’s license.
High Frequency (HF)
3 Mhz – 30 Mhz
HF includes the frequencies in the range of 3MHz to 30MHz. This includes the Ham bands of 160, 80/75/60, 40, 30, 20, 17, 15, 12, & 10 meters.
HF is where Ham radio communication begins to shine, IMHO. Besides “line-of-sight” and “ground wave” propagation (out to about 30 miles), HF radio signals have the ability to bounce off of layers in the ionosphere (“skywave”) and travel around the world.
HF can even be used to communicate underground! (think caves and mines here) With the right antenna setups, terrain obstacles such as mountain ranges and deep valleys are no match with HF communications. This is why the military uses HF to communicate with its forces.
HF Ham frequencies are open to Hams with the minimum of a General license, although there are a few minor band areas open to Technician licensed Hams who want to communicate with Morse code only (Morse Code communications are referred to as “Continuous Wave” or CW by Hams).
There are also some specific frequency allotments that are for use by Hams with the higher Amateur Extra class license, as these take more experience and knowledge to operate in.
HF communications offer the biggest array of frequencies and modes to operate in, allowing Hams to utilize these to match the varying operating conditions that might be encountered.
BASICS OF RADIO PROPAGATION
Radio is pretty basic, right? You push the button on your radio mic and talk. The radio sends out signals to your buddy who is tuned in to the same channel, right? Who needs to understand the “stuff in between”?
Well, the answer is we all need to learn how radio waves work. Why? Because there are many factors affecting radio transmissions that can mean the difference between communicating with a distant contact, or not. In emergencies we need to know what we can depend on for communications.
Radio waves do travel along and through the ground. (And you thought they only traveled through the air didn’t you?) Well they do. Depending on the frequency and power level you are broadcasting at, and conditions in the ground, radio waves for our use may be able to travel out about 25 miles.
Line of Sight
This is what most think of when we speak of radio transmission. Radio waves traveling through the air, above the ground, to a distant contact. Depending on atmospheric conditions, and the frequency used, these waves can be used to communicate out to 30-50 miles.
Hams use “Repeaters” to extend their line of sight communications. Basically, this is a special radio relaying system. You transmit your signal on an “Input frequency” which the repeater receives, then it re-transmits your signal out on an “Output frequency” which the receiving station picks up. Repeater Associations across the country locate and maintain these repeaters at high elevation points to extend their coverage area. Most Repeaters are set up for VHF and/or UHF frequencies, and most are open for anyone to use, but they require special operating codes to use. These all can be found online or in a repeater directory that is published by the ARRL (American Radio Relay League, ARRL.org)
A special series of Repeaters involves Ham Satellites that course the skies above us. Yes! Hams can use these for long distance communication in the UHF/VHF frequencies too, but these are not really reliable for everyday use.
This is the main realm of Ham radio and is generally referred to as “Shortwave”. Here the radio waves are projected towards the upper atmosphere into the ionosphere. The ionosphere is in the upper reaches of the atmosphere bordering space. It consists of several layers, made up of charged ions that have the ability to bend radio waves along their path. This is Frequency dependent.
Hams using High Frequency radio bounce (skip) their radio signals off these layers and they have a tendency to bounce around between earth and these ionospheric layers, in short traveling around the world.
Skywave transmissions are usually good from 400 – 1000’s of miles out from the transmitter. Note that I said from 400 miles out. Skywave transmission usually creates a ‘dead coverage area’ roughly 400 miles in radius out from the transmitter, an area were the radio waves are all heading up and skip over this area. The size of this area is affected by the antenna type and height. Most Hams want their antennas to be as high as possible so they can transmit their signals over long distances.
There is a phenomenon called NVIS, or Near Vertical Incident Skywave transmission that Hams use to cover the normal ‘dead coverage area’ of 50-400 miles (like a doughnut) caused by the gap between groundwave, line of sight and skywave transmissions.
Here Hams direct their radio waves nearly straight up, and they bounce off the ionosphere and come back down all around them. (Kind of like pointing a hose straight up on a summer day with the water falling all around you in a circle.)
NVIS transmission only works on the lower frequencies. 40, 60, 80, 160 meter Ham bands can be used in NVIS mode.
NVIS transmission is what the military uses for reliable, close in communications with their combat troops. It allows Hams to get transmission coverage in an area about 600 miles in radius around them. Anyone in that circle can receive communications, as the signals are coming almost straight back down from the ionosphere! (so deep valleys and high mountains are no obstacle!).
Hams utilize NVIS by mounting their antennas close to the ground, which directs the radio signals nearly straight up. With this setup to be effective, both transmitting and receiving parties need to be transmitting in NVIS mode.
Caveats, Recommendations, and Conclusions
As you have just read, there is a lot to radio communications. There is a whole lot more that I did not address. There are so many variables that affect radio communications that all my comments above must be classified as “In General”, there are plenty of exceptions to be found in real life! Amateur radio operators (Hams) spend their time investigating all the different frequencies, operating modes, signal types, as well as a myriad of radio equipment and antennas. It is a broad area of study!!!
So where do you start if you are new to radio??? I would recommend you start first with the American Radio Relay League, or ARRL for short (ARRL.org). This is a group of amateurs that has been around since radio began, and is dedicated to education of radio to everyone who wants to learn. They have many books on the subject available, and also promote education for licensing.
Why get a HAM license??? Because it allows you to legally transmit on the ham radio frequencies. If you want to learn about radio communications, the best way is to get out there and do it!!! Licensing involves taking tests for each level, but not to worry. The Federal Communications Commission (FCC) that oversees the licensing publishes a pool of all the questions and answers for each test. Easy-peezy!!
The Technician’s License that allows you to use the 2 meter-70cm “handi-Talkies” is only 30 easy questions, and even 8 year old kids have gotten their licenses!! After getting a technician’s license, you can go on and study for your General License. (you don’t even have to know Morse code anymore to get a General Ham License!!) Having a General license will open up the majority the High Frequency Bands, and also allow you to setup and train on using the very reliable NVIS communications!
Radio Communications and Ham radio is a wide area of study. I hope this primer has encouraged you to investigate it further. Here are a few websites that you can start you on your way.
written by “Minerjim”
American Radio Relay League – ARRL.org – National organization promoting ham radio communications and education.
eHam – eHam.net general ham radio website
AMSAT – Amsat.org – AMSAT is the Amateur Radio in Space organization.
AC6V.com – website with lots of HAM radio links.
DXZone.com – another good ham website.
Continue reading: Portable Shortwave Radios for Listening