When using CB's or ANY "broadcasting" radio equipment for communicating, remember that the enemy may have Direction Finding stations operating. This is called "DFing" for short.

To understand how this works you must first understand how radio signals work. Radios usually "broadcast", meaning that their signals extend outward from their antenna much like waves created in a pond by tossing a rock into the center of it. To think of this in three-dimensional terms it would be like a round balloon growing outward, and larger, from the antenna as the radio transmits. This is over-simplified, but it is the concept that is needed to understand DFing.

All that is needed to DF is some basic Trigonometry and two radios with directional antennas separated by about 500 yards... a wider separation is desirable but 500 yards will still work. Once someone begins transmitting on a broadcast radio, both DF radios turn their directional antennas until they find the strongest signal... basically the two DFing antennas end up pointing at the transmitting antenna. Info on direction from the two DFing antennas is overlaid and they simply draw a straight line in the direction both DFing antennas are pointing until they form an " X ". The center of the X is where the transmitting radio can be found... it is now a simple matter to call in artillery or send out a combat patrol to destroy the people working the transmitting radio.

If done by professionals, DFing can be done on a radio that transmits for under 1 second, and can come within inches of it's location from many miles off... especially FM radio transmitters! Ham radio operators have "field-days" and do this for fun.. they call this "Fox Hunting". A ham operator goes out with a hidden transmitter and another group with very simple (sometimes homemade) DFing equipment goes out and finds The hidden transmitter!

DFing CAN be defeated though!

By transmitting in a tight "beam" with a directional antenna or using laser communications, it is possible to make the searching enemy waste manpower and resources looking in the wrong direction since they cannot truly tell where the center of the X is. You are no longer "broadcasting" from the center of a signal... but are more like shooting an arrow at a target. There is no true center, therefore it is MUCH harder to pinpoint a location.

Now... this is where CB radios can be made to shine. Citizen band type radios are AM (which stands for "Amplitude Modulation") radios. To put it in simple terms: with AM, the louder you talk, the more power you put out. A loud noise in the mic causes the radio to put out more power than is put out by just keying the mic with no noise. By talking closely to the mic in a loud voice you put out more power, by talking normally you put out less power... knowing this you can now defeat DFing equipment at least for a few extra seconds (which is all you need if you have codes worked out). Talk loud and then soft and repeat this action. The DFing people's signal strength meters are "confused" because it thinks you are moving around... It gets a strong signal and then a weaker signal. This method doesn't throw them off much, but it's enough to buy you time.

Along the same lines, you can defeat DFing by the use of Linear amplifiers. By quickly turning your transmit power up and down (between 2 and 200 watts) you Again confuse the signal strength meters in DFing equipment. This method works VERY well...Most times the enemy will "pinpoint" you several miles farther off than you actually are! For the same reason, Side-band (commonly called SSB) Radios Are excellent for confusing DFing equipment. If you key the mic on a side band radio it puts out NO power at all until you speak, and then the power level fluctuates wildly as you talk.... And you can talk much farther using SSB than with a standard CB radio!

Another thing to be considered is to ALLOW the end of your transmission to be pinpointed. All kinds of nasty surprises can be left behind for the enemy patrol that's looking for you.

In the Army we could call down artillery strikes on a one second FM transmit pulse, and destroy the radio that made it, in under 2 minutes. Use this as a reminder to maintain radio discipline during hostile conditions.

 

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