Directional Antennas For The Small Unit, Part 1, by NC Scout

One of the biggest misconceptions behind communications security revolves around misunderstanding not just the role of the equipment but also how it functions. A big part of that is the basics of antenna theory. For most radio seems to be a plug and play kinda deal- it either works, or it doesn’t. Antennas are a type of voodoo magic and the solution to security is electronic encryption. Except it isn’t, and doesn’t do anything except mask what you’re saying, but not the fact you’re saying it. Guerrillas must rely on not being detected- and no matter how high tech you think you are, it’ll not solve a tradecraft issue.

The reality is that we’ll be working with equipment that is common and off the shelf- no matter how much we want those microwave NSA-encrypted troposcatter radios made of unobtanium, a big part of local networking is done via plain old VHF and UHF amateur and commercial gear that’s common. Guerrilla communications have to be harder to detect. And at the strategic level when building an underground network, you have to understand how to plan. Even with the cheap equipment most of you likely have, incorporating a level of planning into your local communications will yield a much higher level of security and success. Knowing and understanding directional antennas becomes a key part of that planning, and as we cover in the Advanced RTO Course, there’s several options that each get the job done.

Directional Antennas such as this Yagi seen here offer security by ‘beaming’ our transmission in the direction its pointed.

Directional antennas accomplish two goals for us. First, generally speaking, if you’re not in the direction of the transmission you’re not going to hear the traffic. Because of this it offers a big advantage in the security department. If two directional antennas are transmitting toward one another, they’ll be able to communicate with the only people hearing the full conversation being in the middle of the two people. The second advantage is that instead of all our energy going in all directional at once, as with an omnidirectional antenna, a directional antenna sends the same amount of radiated energy in one direction- greatly increasing our range and signal strength in that direction, so we won’t need nearly as much power to accomplish to reliably communicate over a distance you might not have thought otherwise possible.

Antenna Theory For Non-Technical People

Radio waves travel at the speed of light. So with that said think about your antenna as a type of lightbulb. The more efficient your antenna, the brighter the light (your signal). The more power plus efficiency, the brighter the light and the more range you get. While we measure light in terms of candle power, we’ll measure our signal strength in decibels (db) and our efficiency in terms of gain. Here’s where it gets tricky, but we’ll break it down simple.

A light in the darkness- it the same visual as you would see if an omnidirectional antenna emitted light. That light is a lot like your signal.

Picture yourself in a dark room with no windows. What most people consider antennas could be thought of like lightbulbs in the center of that room. They light it up, but there’s shadowy corners and nothing is as bright as it could be. Where that light goes is just like your signal. And everyone in that room with a set of eyes will immediately know where the lightbulb is. So maybe you don’t want a bright light in the middle of the room, maybe you just want a flashlight to see one corner- to “see” the person you’re trying to communicate with. You’d want a flashlight- and that light directed in one direction will go much further with the same amount of power (or much less) while not lighting up everyone else in the room. That flashlight is a directional antenna.

The antenna you see here is really only half of the picture- the body of the vehicle serves as its groundplane, otherwise known as a reflector. Being in the center of the roof it provides an equal reflection in all directions.

Now let’s explore antenna theory a bit more, now that we have a frame of reference. What most consider an antenna- that thing sticking out of the top of your HT or off the top of your truck, for example, is actually half of an antenna. It is the radiating element- where the signal energy from the radio actually comes out. You could also call this the “hot” side. That radiating element is exactly one half of your antenna. The other half is what’s called the ground plane, which reflects the radiated signal. This would be the “cold” side. So if you’re looking at a flashlight, you’d see the bulb and the mirror behind the bulb. Just as the mirror is a type of reflector, so is that cold side of your antenna. And now the trick is to get that reflector to reflect in the direction we want the signal to go.

Tying the Concepts Together

A directional antenna’s signal would look like this, versus the lightbulb example above.

So just as our flashlight takes a small amount of radiated light and sends it much further than a simple lightbulb in the center of a room would, so does our directional antenna. A lot of folks frequently ask “how much range will this thing get?” when asking about individual radios, and with line of sight gear such as the basic Baofeng, you’re going to get a heck of a lot more in one direction than you would with omni-directional antennas, while greatly improving your own communications security. If you can master the basics while thinking a little bit outside the box, you’ll be surprised at what can be done.

In Part 2, we’re going to cover the antennas you’ll need and how they work.