Editor’s Introductory Note: For those who are unfamiliar with the term “YagI”, I’ll preface this article with a bit of history from the InfoGalactic wiki: “A Yagi–Uda antenna, or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array; these elements are most often metal rods (or discs) acting as half-wave dipoles. Yagi–Uda antennas consist of a single driven element connected to a radio transmitter or receiver (or both) through a transmission line, and additional passive radiators with no electrical connection, usually including one so-called reflector and any number of directors. It was invented in 1926 by Shintaro Uda of Tohoku Imperial University, Japan, with a lesser role played by his instructor, Hidetsugu Yagi.”
To follow up on my last article, Using Military Principles to Improve Civilian Communications, I’d like to discuss a particular type of directional antenna. This is the most practical directional antenna for the common man. This is because a directional antenna is essential equipment — more important than the transceiver itself when pursuing a higher level of Communications Security (COMSEC).
The characteristics of a 3-element Yagi antenna in the UHF band instead of the VHF band as the most important directional antenna that provides the most utility. These are inexpensive and easy to build, and easy to maintain. In comparison, the VHF band is crowded, and a 3-element VHF Yagi is roughly three times larger, and it is relatively cumbersome for a patrol to use.
The UHF band is relatively quiet compared to the VHF band. There is roughly 11 megahertz of usable bandwidth on the VHF side, whereas there is potentially 50 megahertz of bandwidth on the UHF side that we might have access to while conforming to FCC regulations. If I could have only have one directional antenna to reduce the odds of being located via direction finding (DF), and to maintain a higher level of COMSEC, it would be a UHF 3-element Yagi for a low-quality transceiver, such as a ubiquitous Baofeng. Any antenna with more than 10Dbi gain when used with a Baofeng UV5R could over the course of time make this transceiver “deaf”, that is, damage the filters on the receive side of this transceiver.
If I had a Yaesu or better level of equipment, as the next step up, I would use a 6-element Optimized Wideband Antenna (OWA) for use in patrolling work. And the same antenna as a minimum on the base station side of the communications circuit. A patrol will however, most likely use something like a Baofeng, and even if it does have Yaesu handhelds, it would be much easier to point a 3-element yagi toward the base station, since it has a much broader RF footprint. Fortunately, a patrol moves whereas a base station is usually in a static position and therefore easier to DF. Therefore, a directional antenna with 5+ elements is justified at the base station.
Ideally, for point-to-point — that is, between two ‘base stations’ — I would use up to a 12-element UHF Yagi antenna that has a very narrow beam or RF footprint. And I would use a field telephone to remotely operate a transceiver as far away from the base station or TOC. Perhaps up to a mile away during high threat levels. I would also use a directional antenna, if it satisfied the operational requirements at that time. We can make such an antenna by simply adding additional directors of the same length onto a 3-element Yagi and spacing the fourth element 0.15 wavelength apart, and then spacing each additional element thereafter at 0.25 wavelengths apart. I mention this for those who wish to pursue a higher standard of COMSEC, and have the time and equipment necessary.
To keep the discussion practical for the purpose of this article and for typical users, when selecting a general use antenna as a standard for an operation, the 3 element antennas discussed are the best balance of performance and handling in the field, and they will match the lower quality of the equipment most RTOs will have access to. A 5-element Yagi is better for the same purpose, yet it does not best fit into the parameters stated for entry-level work. It requires more skill and better quality transceivers than the Baofeng, Wouxan, or Anytone transceivers, lest it deafen the receive side.
The Virtues of a Wide-Band UHF Yagi
The broadbanded Yagi (425 to 470Mhz, or 50Mhz of bandwidth) is well worth the extra material cost and time as it covers the 70cm, UHF business band, and GMRS. It is like having different Yagis with requisite cables for the cost of one. And, as a single antenna, it takes up one fifth the real estate on the antenna farm. It is however not the best Yagi for DF work, yet it is exceptionally versatile in that it can be used to transmit on 50 megahertz of UHF bandwidth — versus only 10 Megahertz that a standard 3-element UHF yagi can.
The broad-banded Yagi is ideal for a base station or civilian-style Tactical Operations Center (TOC) for TEOTWAWKI when and where we need to make changes to our signals operating instructions (SOI) to maintain a higher level of Communications Security (COMSEC). It is ideal for any mobile or handheld transceiver used in a role as a base station transceiver, because of its gain: It is less than 10.5Dbi, as typically 3-element Yagis are. It will not overload and damage inexpensive and low-quality transceivers (like the Baofeng UV5R) on the receive part of the transceiver and become ‘deaf’ to weak signals. More about this wide-banded Yagi can be found in this article that I authored: Building a EWB/UHF Yagi – Part 1, by Tunnel Rabbit.
Compact Yagi for Portable Work
A simple and easy to build 3-element Yagi that covers 460 to 470Mhz (GMRS) or 10Mhz of bandwidth that is shown in the photo, was made in less than 15 minutes using 1/8th inch diameter brass wire and wood screws. The wire radials can be rotated to be inline with the wooden beam making the yagi very compact 1.24″ w x 14″L. The build can be durable, and is not as easily damaged by abuse in the field, and should it become damaged, it is easy to repair in the field using nothing more than a multi-tool, a spare screw or two, and a pre-cut spare element or length of wire.
We are considering a build for GMRS as this radio service is one that anyone can have access to with a no-test license. This Yagi would cover GMRS simplex and GMRS repeaters. A similar Yagi tuned for the 70cm Amateur band is just as easy to build. For a better Yagi for 70cm, then just do a web search for a build designed for Fox Hunting. These designs are ideal.
During this search, you’ll run into 2 Meter Yagis for Fox Hunting that use scrap spring steel 1 inch tape measure sections for the elements. These are perfect as the elements that can be folded in half for field carry. These are broad-banded enough that they can be tuned for the first 3 MURS channels and the upper part of the 2 Meter band. I painted mine with a flat OD green paint that did not detune the antenna. Use Krylon paint if possible, or be prepared to re-tune the antenna. It is best to paint them before the initial tuning to perfection.
Field Expedient GMRS Antennas
A 3-element Yagi using wire has the advantage of being easier to tune and construct, and the cost of materials is as low as it gets. With the exception of the cable itself, the rest of the materials can be sourced from what is at hand in most homes, or found in the field. The cable could be RG-8 that has 50 Ohms of resistance and is designed for most transceivers. But if an SWR of no less than 1.5:1 is acceptable at the center frequency, then you can use 72-Ohm television cable that is found in most homes.
A PL259 cable end can be attached to cable TV wire RG59 or better yet, RG6 by compressing the aluminum outer shield of the cable in the threads of the PL259. It is possible to attain a SWR of 1.1:1 with 72-Ohm cable if the cable length is as close as can be measured in 1/2 wavelength. In the case of a GMRS Yagi, if the 72-Ohm cable is cut with a multiple of 12-inch increments to the desired length. For example, if we need around 15.5 feet, the round up and cut at 16 feet.
If we do not have an SWR meter, when using 72-ohm cable, it is best to cut as close as one can to the center frequency of a narrow range of frequencies that one plans to most often be using. GMRS simplex frequencies are between 462.000 and 462.750 MHz. Thus:
(234/462.375MHz = 0.506 inches x 12 (inches) = 1.01 feet = 1/2 wave length.)
GMRS repeater frequencies are between 467.000 and 467.750 MHz. Choose a center frequency for either simplex or a repeater, and the SWR will most likely be acceptable using 72-Ohm cable (RG-59 or RG-6) regardless of the length of the cable.
Field expedient antenna building, trimming, and matching are some of skills that a RTO should have. It is possible to use field expedient materials and the measurements provided in this article to make a GMRS Yagi antenna that has a usable SWR without the aid of a SWR meter. As I’ve mentioned before: Use the lowest power setting and keep the transmission as short as humanly possible, and it will do the job. Note all of the the antenna measurements in a notebook, for future reference.
Also note how to make a field expedient dipole made from measurements in a notebook using standard RG-58 or RG8x cable as the antenna material. From memory, I have 12 inches for the radiating element, and 1 1/8 inches for the ground plane element that would be the outer shield. Hoist this crude antenna at least 15 feet high, and the range can be tripled. Generally, the higher the antenna, the greater the range.
To make a 3-element Yagi for GMRS, here are the lengths of the elements:
Reflector: 13 inches
Driver: 12 13/16 inches
Director: 10 3/8 inches
Spacing is measured from the center of each element:
Reflector to Driver: 5 3/4 inches
Driver to the director: 3 3/8 inches
If no SWR meter is available, then operate nearest to the center frequency as is possible that the antenna is designed for. Given that this antenna is intended to operate between 460 to 470MHz with an SWR of less than 2:1 at the extreme edges of it’s range, transmit near the center frequency that should be 465 MHz, when it was originally and properly tuned with a SWR meter, and should be close to 1.1:1 or less than 1.5:1.
For GMRS simplex, the closest frequency would be on channel 8, or 462.750 MHz. Having built many antennas, I know that it is unlikely that transmitting in or around 465 MHz that the SWR would be in excess of 2:1. Of course, if we are using transmit times of less than 5 seconds, then an SWR of 3:1 would not heat up the finals and damage the radio.
ComparING the Moxon and Yagi Antennas
By comparing a 3-element Yagi to the Moxon antenna, we’ll learn more about the 3-element Yagi. The Moxon is a good choice in other circumstances. As we can see from the photo at left of a UHF Moxon that is above a UHF Yagi, both are tuned for the same frequencies. It is readily apparent that the Moxon is more compact. The Moxon also has a much better ‘front to rear’ ratio that better keeps the signal from escaping to the rear and a better ability to reject signals from the rear. Should there be a jamming attempt, the deep null of the Moxon will better attenuate that signal. The deep null of the Moxon can also be used for DF work. However, the homemade wire Yagi can be made more compact for transport or storage by simply rotating its wire elements. (See photo at right.)
The directional RF pattern of the Yagi is tighter, roughly 120 degrees versus the almost 180 degrees of the Moxon, and the Yagi has slightly more gain. Of course, gain is not the most important feature, yet gain is proportional to directionality. The more elements or directors, the tighter the beam of RF radiation, and the greater the increase in signal strength or ‘gain’. The homemade wire Yagi is a better choice as a handheld directional antenna for use in the field than is the Moxon.
It is easier to produce a broad or narrow-banded Yagi antenna for UHF frequencies than a comparable Moxon antenna. The gain of this 3-element direct-connect type of Yagi is no more than 10.5dBi. The Moxon antenna has less gain, no more than 7Dbi and its radiation pattern is much wider, and thus it is less secure.
The Yagi has enough gain that when signal loss in the cable is considered that it increases the Effective Radiated Power (ERP) by 2 times or 2.5 times. This means a Baofeng operated on high power of 4 watts has an ERP of about 8 to 10 watts. When using a high-gain antenna, either directional or omni-directional, always power back to the lowest setting. 10 watts of power can be intercepted up to 100 miles away by an intercept site with an antenna located high atop a mountain that is 4,000+ feet above the average elevation of your terrain.
Construction Details
This simple design keeps costs contained, and production is possible in an austere environment, when resources are severely limited. Again, it uses common materials that are low in cost and easily sourced just about anywhere. All that is needed is a light gauge wire of any kind, such as coat hanger wire or a solid copper wire, a fairly straight piece of wood, and common wood screws. The cable need not be soldered to the radiating elements as good contact can be made by compressing or holding the bare wire of the cable to the wire radiating element by tightening a screw to firmly hold them together. I’ve standardized on PL-259 connectors that are also easy to use in the field. The center wire of the cable can be soldered using light gauge 0.8 mm solder, flux, and a lighter. The outer shield can be connected by crushing it in the connector threads.
Except for the more expensive and specialized versions of commercially produced Yagis that offer elements that can be detached from the beam, most commercially produced Yagis are not as well suited for field work as this humble homemade version, as seen in the photos. Standard commercial Yagis are of better quality and yet are not too expensive, and are best used at a base station, and are a better choice if one does not have experience at making durable antennas. Buy the best you can get, or learn how to make your own using an SWR meter. That is essential gear for the aspiring Radio Telephone Operator (RTO).
Conclusion
Before buying yet another Baofeng, consider constructing a low-cost 3-element Yagi. I have it on good authority that small drones are now being equipped with frequency counter technology and can be programmed to target certain frequencies. The future looks grim if we must protect ourselves from robotic weapons with advanced technology that are also guided or coordinated by artificial intelligence computers that can intercept, interpret radio traffic, and attack at will, using a vast network of drones.
This is why I have the ability to transmit remotely using field telephones from several miles away if necessary. I also have the ability to deploy other heretofore unmentioned and unconventional low-tech techniques to counter this new age electronic warfare.
I recommend that you purchase a drone detector from Brushbeater.com for about $500. And for about $200 get a Tiny SA at the same place that is the newest and best signal intelligence tool that the average man can afford. The Tiny SA is superior to any USB dongles, for the purpose. If I could afford it, I would get the Tiny SA first. See the videos that N.C. Scout has on his YouTube channel, or visit his store at Brushbeater.org. Tell him that Tunnel Rabbit sent you.
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