The case for using directional antennas to contain signals within an area of operations (AO), has hopefully been adequately made in my previous SurvivalBlog articles. Today, I will describe how directional and omnidirectional antennas can be used with MURS Dakota Alert Sensors.
With the advent of HF equipment that can now be operated on very low power, there has been a growth in interest among some Amateur radio operators in QRP (low power). It is a style of HF (High Frequency, a.k.a. shortwave) radio that challenges operators to communicate very long distances using only very low powered transmitters. This style of radio includes small pocket sized transmitters to modern full power sets that can communicate a crossed oceans using only very low power. The pursuit requires more skill and different techniques than is required when operating full powered HF transceivers. It usually requires the use of digital modes and CW, instead of voice.
Operating VHF/UHF transceivers instead of HF sets on very low power also comes with certain technical challenges that are different than what is required for QRP using HF. QRP is not usually associated with VHF/UHF Amateur bands above 40 meters, and so there is little interest, and little known about how to go about it. Yet there is little new under the sun. Military operators in past eras have done so on a regular basis.
Unfortunately, those skills are long gone and we might have to reinvent the wheel. QRP is challenging, but if we wish to avoid interception, low power is our friend. With the previous few articles about operating on low power, my hope is that more Hams will develop an interest, and use their experience to pursuit this method of operating. There are parallels. Instead of using a Beverage On The Ground (BOG) antenna to receive weak HF signals, and a sloping dipole to send, we could use a high gain directional antenna to listen, and low gain omni or directional propagation techniques to transmit, if we wish to limit our audience.
Given that VHF/UHF is used, we can use terrain features such as hills and rock faces, or buildings to block, or reflect propagation to our advantage. Low power operation also means we can use common equipment, and less power is required to sustain an operation in the short, and long run. Like any other style of radio, the challenge can be interesting and fun as well. That is of course, if you are also a radio geek like me. Although repetitious in spots, sometimes it pays to reiterate, or hit the same topic from a different perspective. In the following, I attempt not to ‘geek out’ too much, but provide helpful information based upon my experience. This stuff is not hypothetical. It works.
MURS Dakota Alert IR Sensors and External Antennas
The advantages of using directional antennas to contain signals, and extend the range of low-powered transmitters within an AO, has hopefully been adequately made in a previous article: Communications: Bringing People Together – Part 1  and Part 2 .
This article is another attempt to help others new to radio understand how directional, and omnidirectional antennas can be used with MURS Dakota Alert Sensors, and other low power transceivers. While the focus is on the sensor, the same discussion applies to low power handhelds, such as the common, Baofeng or Wouxan, as well. We can install an external antennas on various brands these devices to dramatically increase their range and utility, and thus improve our security operation in general.
The sensors transmit using just over 1 watt with a VHF frequency in the MURS (Multi Use Radio Service) band. These are a low-powered transmitter that uses sub-optimal antennas that propagate their very low-powered signal poorly, resulting in very limited ranges. The original telescopic antennas were much better propagators, but had a tendency to allow water to infiltrate the housing. Although now designed to be more weather resistant, the current versions of these sensors has a shorter, and even worse-propagating antenna.
While a shorter-range antenna can be also be advantageous, it would also be good to begin our defenses at the furthest most possible distance from our mailbox as possible. Therefore, it would be more advantageous to be able to use these devices at the greatest distance possible that our equipment and techniques, and the surrounding terrain allow. Extending the range requires extra work, but the benefits can be priceless. This can be accomplished by using a more efficient radiator (antenna), that is conversely, a better receiving antenna, on one or the other, or both the transmitter and the receiver.
Early Warning Provides Additional Time to Respond
MURS Dakota Alert IR sensors are now well-known to most preppers. These are particularly useful for those who lack the manpower to stand up a larger security force, or to support a security operation that can put eyes onto a possible threat. In no way do I suggest that an electronic device is as reliable as eyes and ears at tactically well placed LPOP (Listening Post/Observation Post). Properly, they should be used to provide support, or improve any security effort, and to provide an outer layer in a layered defense. Use them alone only as a last resort, when you are operating with scant manpower.
Appropriately placing obstacles or barriers, and other methods of delaying, or reducing the speed of an approach, can provide more time to respond. Creatively combining various techniques together, can have a synergistic result, thus further justifying the expense and effort of establishing any force multiplier, such as Dakota Alert sensors. For the sake of brevity, I’ll focus on extending their range. Perhaps later, we can explore how these sensors can be deployed in a tactical way. To minimize false alarms, use lithium batteries and use two sensors separated by more than 30 seconds in distance for the typical mode of transportation for the trail or roadway. The amount of power that these will transmit with decreases as the battery voltage decrease. If rechargeable batteries must be used, replace them often, or before the voltage drops below 8 volts. A larger battery with a PV panel can also be used.
If placed along a rough dirt road, place the second sensor at the distance that a typical vehicle can travel down such road in 30, or preferably, even more time. The sensor needs 30 seconds before it will reset, and will provide another alarm message. Placement of the sensors in this way provides one with the ability to not only verify an approach, but also can be used to determine a direction of travel, either ingress or egress, of a single vehicle, or the approach of several vehicles.
To those who wish to enhance their security operation, the use of external antennas can improve their usefulness as the range of these sensors can be greatly extended. (As a side note, it is also legal to do so.) As I have personally used many of these sensors in a systematic way, and at ranges up to 6 miles away that was received with an attached antenna on a Baofeng UV5R, that is the least effective transceiver and antenna combination for this job. Other transceivers and external antennas would be far more sensitive to weak signals.
Various methods of deployment can also improve their usefulness. As electronic eyes to provide early warning of the approach of a potential threat at ranges up to many miles away, from personal experience, this is feasible, if suitable and favorable terrain are present. Based on previous experience, I am currently designing such a system for property of considerable size that requires a sensor range of several miles. There is no guarantee that the effort will be a complete success, yet what can be done will extend the useful range, and improve security.
If the terrain is favorable and the range extended, the precious additional minutes to respond, could be life-saving. If living in a remote area, or on a large property comprised of hundreds of acres, or surrounded by USFS lands, the method and additional expense could be justified. These sensors can also be installed inside of a building and connected to an external antenna if necessary. One could be several miles away and be alerted that a vehicle is approaching the residence, and approximately where it is along that route, And with more sensors, you could be alerted if intruders entered a building that is protected by a sensor inside. Or, you could determine if they have changed their direction and are leaving the area.
Because I build my own antennas, the expense is a small fraction of the cost of purchasing commercially made antennas. Making my own antennas, antennas that could cost more than the sensor if purchased commercially, has made these techniques economically feasible for me. It has also allowed experimentation for many years, and in ways that few others have reported.
Discussion of external antennas on these sensors is not new, yet is limited to a few examples, but use of external antennas (omnidirectional and directional) for use at extreme ranges, to my knowledge, has not found its way into the literature. I haven’t seen it yet, so unfortunately, no other source is out there to verify these methods. Consider the method to be experimental, yet feasible. Should this unusual method work, it is a force multiplier few have encountered and would likely anticipate. If attempted, it is likely that some success will be achieved, and the effort will not be a total waste of time.
(To be concluded tomorrow, in Part 2.)