Mitigating the Drone/RDF Threat – Part 2, by Tunnel Rabbit

(Continued from Part 1.)

Down and Dirty, Remotely Controlled Transceivers

Armed with the axiom that if something is ‘stupid, but works, then it is not stupid’, we can become creative. In the most austere environments where field expedient and unconventional means are the only means, I should mention that a Citizen’s Band (CB) radio with a Public Address (P.A.) function, or a hard wire intercom can also be used with the VOX feature of a transceiver to cause it to transmit. Using these means, we can transmit remotely, yet we can only receive via a transceiver located at the base station. This is not optimal, yet in many situations, it could be perfectly good enough. When it comes to field expedient means, keep in mind that “perfection is the enemy of good enough”, especially if it can save lives.

We can also operate two separate CB radios over two separate runs of WD1a wire as a crude phone system whereby each station can communicate. An intercom can perform similarly, as well. And we can use a C.B radio’s P.A. function to deliver instructions remotely at a checkpoint safely from an LP/OP. Field phones can assist at a checkpoint as well and in conjunction with a P.A. system. It would be good to be able to interview (interrogate) persons at the front gate from a safe distance, especially if overwatch is not available.

RF Propagation Techniques as RF Camouflage

Historically, RF propagation techniques were practiced extensively on the battlefield and were once SOP for our military, from WW2 through Vietnam and a bit beyond. Nothing I’ve mentioned is new under the sun, but proven. How we use it, could be another matter, so it would be good to define what it essentially is: RF camouflage.

Moving beyond field phones, we can use propagation methods as part of a defense. As a metaphor, these methods should be considered as a sort of electronic/RF camouflage that can be deployed on an electronic battlefield. Using one’s imagination, we might be seen or heard, yet we may not necessarily be identified or located. That is what camouflage does in the physical/visual realm. Camouflage does not actually make us invisible. Rather, it confuses the viewer about what he is observing. What kind of camouflage should be used will depend on the terrain, and circumstances.

To learn how to do this, we must understand how RF works in the field, and consider the equipment, and the level of talent that operators in the field possess. Art takes the science behind this endeavor to a higher level. This is something that anyone should aspire to, myself included. It requires a certain level of experience and knowledge that cannot easily be conveyed. By no means are what I’ll describe in teh rest of this article exhaustive. It is only an introduction to a few of the RF propagation techniques that can be employed to mitigate potential threats.

Other Drone/RDF Mitigation Techniques

There are other techniques that might be helpful and confuse a drone’s operator. These means can be used in conjunction, or alongside remotely operated transceivers. Even if this article can not provide all the answers to this problem, it might provide some “food for thought and grounds for further research.” As one example, higher-tech solutions to drones involve jamming the remote control signals that the drone receives from the operator’s controls. Unfortunately. I cannot afford to acquire such a capability. Therefore I will employ only low-tech counter-drone measures.

Hopefully, we would avoid detection entirely using a network of low-powered transceivers, directional antennas, terrain masking, and other techniques, if our network of field phones, or commercial phones, is not sufficient to cover the Area of Operations (AO) that includes our closest neighbors first. We should strive to maintain radio silence by using field phones as intercoms between homes. However, a patrol, or distant neighbors would require radio communications. By carrying a lightweight TA-1 sound-powered field phone, or a lighter in weight commercial phone, a patrol could use the same wire that controls a remotely operated transceiver, or a wire that is used to operate a remotely triggered trip wire alarm. And a patrol should use a field phone and a password to gain entrance into a perimeter. However, radio communications would be necessary for all other situations involving a patrol.

We might be able to use a field phone to remotely operate a transceiver from several miles away to communicate to a patrol and neighbors. This method allows radio transmission to occur elsewhere, rather than at a base station. However, if we are lacking sufficient field wire to establish a remotely-operated transceiver, then we can use other methods to reduce the odds that our RF signal could lead others to pinpoint a base station.

Of course, our Signal Operating Instructions (SOI) should include the use of a brevity code, short in duration and low power transmissions, directional antennas, horizontal propagation, terrain masking, and frequencies that propagate less well in our terrain thereby intentionally limiting its range, and even pseudo-random frequency hopping techniques. In addition, we can also use directional antennas and the aforementioned propagation techniques with low-powered repeaters.

Pseudo-Random Frequency Hopping

Here is a brute force, or quite simplified way to create something like a ‘pseudo-random frequency hopping’ communications circuit. There are other ways as well. But this can be accomplished by the use of say 5 to 10 inexpensive Baofeng UV5R transceivers each at both the sending and receiving station. Each set of transceivers is reprogrammed each day with a new set of frequencies. Both stations use all of the transceivers at the same time. If the operators transmits on transceiver #1, the other station will receive on their transceiver #1, but the receiving station would reply by using transceiver number 9, and so on and, so forth, we choose at random a different handheld each time that we transmit. This would keep interceptors guessing, and defeat scanners. By using this crude method, it might be possible to intercept one side of the conversation only momentarily, even if a bank of 30 or more high-speed scanners were used.

Repeaters and Low Power

There are low-cost, low-powered repeaters available. These are methods that constitute a low-tech form of electronic countermeasure. Using any combination, or all of these techniques that would seldom be encountered and therefore not anticipated, could minimize the risk of radio direction finding (RDF) when transmitting. Those who are analyzing information from drones, might overlook the primary source of a transmission, if there is a directional antenna transmitting a weak signal into a repeater that broadcasts a stronger signal widely using an omnidirectional, or perhaps, a horizontally polarized directional antenna, with a greater Effective Radiated Power (ERP) than the original incoming signal.

The repeater could be located well below a hill’s military crest and use the terrain to mask radiation to the rearward or opposite direction, and it could potentially also use low-power transmissions. Use higher power levels only if and when necessary to improve coverage in a low-power radio communication ‘circuit’, if more distant stations, fixed or mobile, require it. Use high power only for those distant stations that require it, but power back for transmission to all other stations. Limit RF propagation whenever possible. Use the correct antenna and techniques required for your particular area coverage requirements. Use increasing specialized and limit propagation for a closer-in security operation.

Low power is our friend if we wish to avoid interception, so use the lowest power setting on the transceiver that makes communications reliable and not more power. Strive to be on the edge of just enough power to make yourself intelligible, and hopefully below a signal strength that many signal strength meters would indicate as below ‘S-1’. For example, we will transmit on a UHF frequency, using only 250mw (1/4 watt) through a horizontally polarized UHF 5 to 12 element yagi, or with the broader RF footprint of a moxon antenna, or a low gain omnidirectional antenna located at mid-height on a hillside. Choose wisely. It would ideally be transmitting into a mountainside where there is located a repeater, and keep transmission times to less than 5 seconds. The odds of our location becoming pinpointed would therefore be substantially lower.

A repeater is by its function and location is naturally more vulnerable and this fact could work to our advantage. If the repeater becomes nonfunctional then it may have been dismantled, or otherwise disabled, and a patrol should put eyes out there to find out “why and by who”. A repeater could become our canary in the coal mine. The risk of using a repeater as a part of our defense is that it can be disabled just before an attack. Be prepared with a contingency plan that does not require the use of a repeater, or the use of an alternate repeater. A contingency plan can use high-powered transmission levels in an  important event, or for when repeaters are temporarily, or permanently disabled.

(To be concluded tomorrow, in Part 3.)