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Thread: Intro to Radio Communications

  1. #1
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    Intro to Radio Communications

    We’re going to distill this down, and help you to get your noodle wrapped around amateur (ham) radio and some of its capabilities.

    The first thing everyone always wants to know is, “How far can _______ go?”

    The answer nobody wants to hear: it varies.

    Fine minutia of technical details will be excluded from this. The intent is to help people who have little or no exposure to the topic of radio communications obtain a fundamental idea of the concepts involved.

    If you take radio communications, and break it down into areas of coverage, which is what the majority of people new to radio want to know, you will begin to see it as follows:



    • Local Communications: Radio-to-Radio – 0-10 miles
    • Tactical Communications: Radio-to-Repeater/Base – 0-50 miles
    • Regional Communications: NVIS – 30-500 miles
    • Strategic Communications: HF Skywave / SATCOM – 500+ miles


    These different areas typically involve dedicated hardware, as well as operating procedures for each area of coverage. For example, the equipment and techniques for Local Communications will not work for Regional Communications, and vice-versa. While there are exceptions, the technical details are beyond the scope of what we’re setting out to understand here.


    Local Communications: You and your buddy are chitty-chatting across the lake to one another.

    At the Local Level, or immediate area, you have Simplex communications. Simplex communications involve a radio signal, transmitted from one person directly to another. Simplex operation is typically in the Very High Frequency (VHF) or the Ultra High Frequency (UHF) portion of the electromagnetic spectrum. The range is, approximately, 0-10 miles. A reasonable expectation is approximately 1 to 2 miles. These types of communications are limited to Line-Of-Sight (LOS) only.

    What LOS means is that as long as you have a straight-line distance between you and your buddy, the two of you can chat it up. If your buddy is in a valley, and you are not, there is a good chance you may not be able to hear each other. You are also limited to the curvature of the earth, which falls at the rate of ~8″ per linear mile. The earth being round and all, means that it starts falling off faster as you traverse along it radially.

    There are ways to mitigate this.

    Height is your friend with VHF/UHF. If you can gain additional elevation, the range of your radio can be extended. For example, if you were to stand on a very large hill, and your buddy is 10 miles away, with no obstructions between the two of you, there shouldn’t be any difficulty in communicating with each other. A way to think of it is that, if you were physically capable of seeing your buddy, even with aid of a telescope, you should be able to communicate Simplex.

    The VHF portion of the electromagnetic spectrum is referred to as the 2-meter (2m) band. The area we are concerned with is 144-147 MHz.

    The UHF portion of the electromagnetic spectrum is referred to as the 70-centimeter (70cm) band. The area we are concerned with is 420-450 MHz.

    The majority of communications in VHF/UHF use what is called a vertically-polarized antenna. This simply means you’re pushing a signal into one end of antenna, that is perpendicular to the earth. Stickin’ straight up in the air, for you non-geeks.

    VHF/UHF radios come in three flavors:

    • The Handheld Radio.
    • The Mobile Radio.
    • The Base radio.


    The handheld radio, or “Handie-Talkie” (HT for short) is exactly as its name implies. These are oftentimes referred to as, “Portables.” They are battery-powered radios, with a small form factor, that can be carried on your person. The typical wattage on these radios is around 3-5 watts. There are some models floating around that can go as high as 10-watts (TRI PRC-148 Clone); however, pumping higher-output from a HT is mostly an exercise in depleting your batteries at a higher rate, without the benefit of a better signal report on the receiving end. I tend to view the HT radio as the most utilitarian, despite its range, due to the fact that it is the radio you are most likely to have with you at all times.

    Examples of affordable, entry-level HT Radios are AS FOLLOWS:



    All of the HT radios listed above offer both VHF and UHF frequency coverage.

    After the HT radio, we have the Mobile Radio. The mobile radio is vehicle-mounted, and they typically have an output of anywhere from 5-75 watts. The mobile radio offers advantages over the HT in terms of higher output, a better ground plane (the vehicle’s body or chassis), and taller antennas with higher gain. Gain is the amount of increase in signal, expressed in decibels (dB). We won’t go into technical details here, but what it means to you is that the radio signal leaving a higher-gain antenna will be more focused (stronger) in a given direction (typically towards the horizon / parallel to the earth’s surface). In general, a properly configured mobile radio should have a greater range potential than a handheld.

    Examples of affordable, entry-level mobile radios are AS FOLLOWS:



    Like the previously mentioned HT radios, all of the Mobile radios listed above offer both VHF and UHF frequency coverage.

    Finally, we have a base radio. This is a radio, operated from a fixed location. A base radio, may not necessarily be any different from a mobile radio, other than its configuration in an overall radio system. For example, while the radio you obtain may be used for either a mobile or fixed application, the application of the radio is the critical difference between the two. With a fixed base radio, you have the advantage of installing a much taller antenna and, through the use of an amplifier, up to 1500 watts of power. Again, like the handheld, more wattage doesn’t necessarily equate greater range, and there is an exponential loss of efficiency as you continue to increase power. A base radio, in theory, means that you have the potential for the highest antenna possible, and the most power possible to use.

    At the Technician level, most of the fixed-station, or base radios, are going to be the same as mobile radios, configured to be run indoors. Since mobile radios are inherently designed to run off of your vehicle's battery, you will need a switching power supply in order to power these from a wall-outlet. While I'm not overly crazy about MFJ's products, this is one of the cheapest power-supplies that should power just about any radio you might have access to as a newly minted Tech: MFJ-4125.

    The VHF/UHF frequencies are not limited to the earth. They will zip right through the atmosphere. This means, that should your buddy load himself up into a hot-air balloon, and take a trip to outer space, he would, for the sake of this analogy, be able to communicate with you.

    The problem with VHF/UHF is that, due to the laws of physics, for the most part it is a means of local communications only. You can pump all the wattage into a radio that you want; you’re still not going to push the radio signal through a mountain, or bore through the earth. Remember, we are limited to Line-Of-Sight…

    Since VHF/UHF radios are limited to LOS, how might we go about milking some extra mileage out of them?


    Tactical Communications: You and your homie talk shop across a major metropolitan area.

    At the Tactical Level we would employ a repeater, or use a tall antenna at a topographically sound location. Typical ranges could be anywhere from 0-50 miles.

    A repeater is typically placed at an advantageous position, such as on top of a tall building, large mountain, on a tower, etc. The repeater will receive your LOS signal, and re-transmit that signal outward in every direction.

    In most situations, the repeater will be operating, not only from a more efficient position, but at a higher effective radiated power output level than what you are sending to it. So, for instance, if you are transmitting at 5 watts to the repeater, it will receive your radio signal and repeat it back out at 100 watts, and from a higher elevation, ensuring that your range is significantly extended.

    Another option, aside from the employment of a repeater would be a well-configured base station. If, at the fixed location, you have a good antenna height, for example at the top of a chimney, or mounted to a backyard-tower, the additional horsepower from higher-wattage, and the taller/more efficient antenna will extend the range significantly, when compared to handheld/portable/vehicle-operated VHF/UHF radios.

    Repeater coverage, just like Simplex, is limited to LOS. The use of a repeater can give a much greater coverage area than Simplex alone, but the laws of physics creep back in, and still limit the repeater to what is within, for all intents and purposes, visual distance. Because the repeater is in a higher location, by default, its visual distance is greater than what you have at typical ground-level in your area.

    So we can talk across town with a repeater, or simplex through base-to-base comms, but now what?

    Up to this point, we have been discussing the application of VHF and UHF radio. The frequencies VHF and UHF are limited to LOS, and we know that they will zip right through the atmosphere and continue into space.

    To effectively go Beyond-Line-Of-Sight (BLOS) we will need to get into the High-Frequency portion of the electromagnetic spectrum.


    You and your buddy, rag-chewin’ from Crested Butte, Colorado to Wichita, Kansas.

    At the Regional Level, we are in High-Frequency territory. The HF portion of the electromagnetic spectrum is also referred to as Shortwave Radio. The area we are concerned with for NVIS is 3-7 MHz. In order to establish BLOS Communications, you would employ a technique known as NVIS, or Near-Vertical Incidence Skywave.

    NVIS is the only reliable way to obtain wireless communications in a coverage area from approximately 30-500 miles.

    Remember from earlier, where VHF/UHF radio waves will go into space? HF, for all intents and purposes, does not. HF frequencies are reflected by the earth’s ionosphere.

    NVIS works by sending a radio signal straight up in the air, perpendicular to the earth’s surface. The signal is then reflected by the earth’s ionosphere, cascading back down in a waterfall back to the surface. The frequencies used for NVIS typically range from 3-7 MHz.

    For NVIS, the most common antenna is a dipole. A dipole, simply means “two poles.” For the sake of simplicity, imagine two sections of wire, with an insulator in the middle. The antenna for NVIS is horizontally-polarized. Runnin’ side-to-side for you non-nerds. For simplicity’s sake, running the antenna low to the ground, and horizontally-polarized, is a technique for ensuring as much of the signal is directed towards the zenith as possible. Basically, straight-up.

    So that’s cool and well, but what else is there?

    NVIS is used to operate in that 30-500 mile radius we discussed earlier. What if you want to go farther?


    Using HF, or Shortwave to Talk to Aunt Mavis in Kuala Lumpur.

    At the Strategic Level, there are a couple of options available for radio communications.

    We’ll start with the most unreliable for ham radio considerations: SATCOM. There are multiple satellites, along with the International Space Station (ISS) that are available to make contact with, or to use as repeaters. While it is certainly possible to make contact with distant stations using a HT, and a satellite in Low Earth Orbit (LEO) as a repeater, it requires advanced tracking of the satellite’s path, and the window of opportunity is relatively short (typically less than 10 minutes of available time). In order to reliably use a bird (Satellite) for comms, both the transmitting and receiving stations would have to be within the flight path’s range, as well, the short window of time, and difficulty in tracking without pre-established flight-paths being published make this a somewhat unreliable form of communications.

    Virginia Tech University is currently in the process of preparing a geosynchronous satellite as a radio repeater sometime in 2017. This satellite would be available for long-distance communications 24/7/365. This may be a viable option for reliable SATCOM, but until the system is on-line, there aren’t any other reliable methods for using satellites consistently.

    The final option for long-distance communication is Ionospheric Propagation, Skywave, or “Skip”. All three terms are referring to the same phenomena.

    This means of signal-extension, not unlike NVIS, relies on the reflective nature of the earth’s ionosphere to bounce signals between the earth’s surface and the atmosphere. For this means of communication, we are still using the HF band to make distant contacts. The area we are concerned with is 3-30 MHz. Ionospheric propagation is dependent upon a lot of variables such as solar cycles and storms, time of day, seasons, etc.

    The ionosphere itself is broken down into three layers:

    • D Layer
    • E Layer (as well as Sporadic E, but we won’t get into that)
    • F Layer


    The D Layer is the closest to the earth’s surface, followed by the E in the middle, and finally the F layer. The F layer is the most dense, and is the layer that is responsible for the reflectivity that is important for skywave/skip propagation of radio waves.

    Once a signal is reflected off of the F layer, oftentimes it will undergo several bounces between the ionosphere and the earth’s surface. Bear in mind, that with each successive “bounce”, the there will be a degradation of the signal strength, both through ground losses, as well as D layer absorbtion. Atmospheric conditions, and solar activity will play a part in the ability to use skywave propagation for communications.

    For both NVIS, and Skywave, an HF-radio is required. While Technician class licensees are limited to the 6m and 10m HF bands; neither of these are suited for NVIS.

    An absolutely excellent radio that one can grow into, is the Yaesu FT-817. It is field-portable, can be run off of batteries, as well as a DC source, (or AC with the use of a witching power supply). If you eventually find the output to be insufficient for your needs, an in-line amplifier can be run to give your signal a little more ass.

    Hopefully, this helped you to understand the fundamentals of radio communications, related, specifically, to ham radio.

    I am asked many of the questions answered here, by people I know personally, and this is basically a simple article on the rough-principles of operation, without a lot of technical jargon, and geek-speak that tends to glaze eyeballs over. It has been my experience that many people, unfamiliar with ham radio, find the subject grotesquely overwhelming, and unapproachable. Can’t start without the basics, and this writeup is about as basic as it gets.

    REVISED 01SEP16 - ADDED RADIO EXAMPLES FOR COMMUNICATIONS RANGES
    Last edited by Outlander Systems; 09-01-16 at 14:22.

  2. #2
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    Very much appreciated Outlander.

    Keith

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    Welp. This is glorious.
    “Answer The Bell...” J.W.

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    Great read. Thanks for putting this together.
    In no way do I make any money from anyone related to the firarms industry.


    "I have never heard anyone say after a firefight that I wish that I had not taken so much ammo.", ME

    "Texas can make it without the United States, but the United States can't make it without Texas !", General Sam Houston

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    Awesome, thanks

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    Absolutely, fellas.

    Hope it helps.

    Shoot. Move. Communicate.

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    Wow that was a solid knowledge nugget. You have any qualms with me printing this off for hard copy storage?


    Sent from my iPhone using Tapatalk

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    Thanks.

    Absolutely, man.

    Feel free to reproduce, distribute as needed.

  9. #9
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    The best part are the pictures.....
    In no way do I make any money from anyone related to the firarms industry.


    "I have never heard anyone say after a firefight that I wish that I had not taken so much ammo.", ME

    "Texas can make it without the United States, but the United States can't make it without Texas !", General Sam Houston

  10. #10
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    Great writeup!
    Black River Tactical
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