by Tunnel Rabbit, Survival Blog:
(Continued from Part 2. This concludes the article.)
Antennas
As an example, factory broad band antennas can suffice, yet performance in terms of propagation and receive will be lacking, and the overall range shortened, and the transceiver’s life possibly shortened. And there are other issues to consider. The crude, yet effective Baofeng UV5R does not power back given an excessively high Voltage Standing Wave Ratio (VSWR) from an antenna, and this situation will shorten the life of the ‘finals’ of this transceiver. If the back side of a Baofeng UV5R becomes warm to the touch, stop transmitting, drop the power setting to low power, or install a properly tuned antenna, or better yet, an antenna that is located as high up as possible, and use the lowest power setting that make communication possible. This is an example of why we need a basic understand of how transceivers work or do not work well, and how to use them correctly.
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Even if we can not make antennas, we need to know that we need to use the correct antenna for a given frequency range, and how use an antenna to limit or extend the range of the transceiver. Often, shorter antennas that limit the range are the most appropriate if we seek to improve COMSEC — that is, when we need not have a range beyond our perimeter. Knowing when to attach an antenna that propagates further is the correct choice and is also a part of what the operator needs to know.
The Radiotelephone Operator (RTO) should also know how and when to use a directional antenna. The RTO will also need to know how to use a map and compass to determine the azimuth they need to point a directional antenna towards the location of a station. A high gain directional antenna can be used to defeat a jamming effort as well as the signal strength generated by the transceiver can be doubled or tripled, and be powerful enough that it over powers the jamming signal. Horizontal polarization of antenna systems will attenuate (weaken) a signal strength heard by a receiver of the interfering signal by up to 20Dbd. This is a significant amount. 3Dbd represents a 50% reduction in signal strength.
The use of horizontally polarized directional antennas at the base station and in the field with a high powered transceivers at both stations may overcome a jamming attempt better than any other available technique other than switching to the alternative frequency that may or may not be jammed as well. Increase the power only as needed and until the jammer is over powered.
Always Expect Jamming
Expect to be jammed by low-powered and high-powered transceivers that use a continuously keyed mic (or ‘open mic’) that will disrupt our communications. Nation states have jammers that jam entire parts of the spectrum. We can avoid a jamming attempt by shifting to another band that the alternative frequency should be on, and by transmitting using a high-powered transceiver and a code word or command to switch frequencies. Using the lowest power setting to avoid detection in the first place, is best.
When jamming occurs progressively increase your transmission power as the more powerful signal strength will open the squelch of receiving transceivers. The higher in power transmission will be more likely be heard than the lower powered transmission from an ‘open mic’ that might be accidental and likely a low-powered handheld. Do not advise on air that the channel is being jammed. Instead, use a code word to initiate the change to the secondary channel/frequency, or during training using an ‘open mic’ to simulate a jamming effect so that participants can recognize the condition and automatically switch to the alternative frequency.
Authentication is Critical for Good COMSEC
As additional security, authentication should be used to validate the call sign user. In the situation where a patrol returns and is seeking entrance into the perimeter, authentication is an additional layer of security that prevents impostors from gaining entrance, particularly in low-light conditions when the patrol can not be identified visually. This is potentially a very dangerous activity. If we allow entrance to a Trojan Horse element that has our confidence, the result could be devastating.
The approaching patrol can use radio, or a field phone that they carry and attach to the line just outside the perimeter in a hidden location. After calling the radio attendant in the TOC or FOB, the attendant should require authentication before proceeding with the conversation. We would use a 10-letter word or phrase where each letter is assigned a number. One example of such a word would be ‘Pathfinder’ and another, ‘Charleston’ or any 10+ letter word or phrase that is easy to remember that does not use the same letter twice. A simple authentication matrix would look like this:
P A T H F I N D E R
0 1 2 3 4 5 6 7 8 9
In the following example, a patrol is returning and seeks permission to enter the perimeter. The communications traffic would sound like:
Patrol: “Squirrel, ‘this is…’ Rabbit (patrol), over”
TOC: “Roger, authenticate 9, 6, 2, Hotel, Echo” (9,6,2,H,E)
Patrol: “Squirrel/Rabbit I authenticate Romeo, November, Tango, 3, 8 over” ( R, N, T, 3, 8)
TOC: “Rabbit/Squirrel, roger. OPENSESAME”
(Translation = Open- says -a- me, and is the code word for ‘authorized’ or ‘ authentication complete’.) If the incorrect code word for entrance is used by the TOC, it is presumed that an impostor is seeking entrance and the Listening Post/observation Post (LP/OP) or guard post will respond accordingly.
With the authentication process complete, and entrance granted, or additional communications authorized, then a report such as a SALUTE(D = direction) report, or a civilian ‘Who, What, When, Where’ report can proceed, preferably face to face, in hard copy, or via field phone, to avoid interception.
The authentication code should be changed along with changes made to the SOI, and be associated with the current SOI. Any use of a previous authentication code with a new SOI invalidates its use and automatically identifies a probable impostor and intruder who attempts to use the outdated or incorrect ‘authentication code word’. It must be assumed that someone is attempting to gain access into the perimeter or to use a false report to mislead and steer our defenses in a direction that is advantageous to the enemy.
Unconventional Methods
As one example, given a strong desire to avoid interception is why we would want to use unconventional techniques that are more complicated to implement and would require additional training. Using a split frequency communications circuit where transceivers at both stations use either a UHF or VHF frequency to transmit, and the same transceiver ‘listens’, or receives the opposing UHF or VHF transmitted by the other station. Thus, most outside listeners would only hear one half of the conversation. To improve their ability to intercept us as before, the enemy would have to double their SIGINT effort. Using directional antennas that are also horizontally polarized in this same network would add many layers of COMSEC.
