Antennas are the underappreciated other half of a transceiver. Back in the day, Hams strove to make their own homemade transceivers. But with the advent of cheap stuff from Asia, we have been spoiled. Now we tend to just buy it. It is time to refresh our skills. While continuing to build antennas for friends and neighbors, and other low-power community radio networks, I’d like to share some of my trade secrets. Secret number one. It is so easy, a guerilla can do it, but only after some trial and error.
A cheap radio on a good antenna is a better combination than an expensive transceiver that is attached to a cheap antenna. As it is with common-caliber ammunition, an easily reproducible antenna, solves a logistical problem. Antennas can and do break, and if I have several spares on the shelf, a new one can be quickly swapped in. And there are many Baofengs, and other transceivers out there that will need an external antenna. As ‘height is might’, a low-powered and inexpensive handheld, or a mobile transceiver on a good antenna, can be much more effective, not only in its ability to transmit farther, but to also receive weak signals from low power transmissions.
VSWR Meters
Before we can build or repair antennas and cables, we’ll need at a minimum an accurate SWR meter. A cheap Chinese SWR meter should be avoided as these can give false readings. Buy a Bird, or other meter, or go whole hog for an analyzer. Old School meters, such as the Japanese made Vanco brand, that can be easily found on eBay, can be a good choice for those on a tight budget. Research the model to see if it can be used for VHF. I would trust one of those 30-year-old meters over anything made in China to be sold at rock bottom prices. The Antenna Farm, with locations in Lincoln County, Montana and in Blairsville, Georgia, has a selection of decent meters, and the customer service is excellent. Buy with confidence as they have a good return policy, but test any new meter against any meter handy that is believed to be accurate. The last five inexpensive meters that I purchased from different manufacturers, were all bad. My 30-year-old meters were used to verify the accuracy of these new meters. Unfortunately my old meters are limited to HF and VHF.
The J-Pole Antenna
Building J-poles and Slim Jim antennas out of 1/2 inch copper pipe, is a good choice as the build is rugged and reliable. It is a practical choice for the novice or experienced antenna builder. And this type of antenna can be used horizontally polarized. One might buy their first j-pole antenna from KB9VBR on Ebay to study how it is constructed, and to test. It is hard to build these at a lower price than to buy from KB9VBR, yet as a guerilla- kind of guy, my goal is to be able to produce a quantity, and obtain the skills to make durable antennas with any available material using only the simplest tools if need be. Here is one of a long list of ‘how-to’ videos. that can be quickly found on YouTube. David Casler does an excellent job of describing how the J-pole works.
The fellow here demonstrates how he deals with some of his mistakes on his copper pipe J-pole build. Instead of an SWR of 1.4:1, he should could have an ideal and low SWR of 1.1:1 at the design frequency, and 1.5:1 and less throughout the 2 meter band. It takes time to learn, and that is best done by doing.
For a variety of reasons, either the 1/4 wave or 5/8 wave ground plane antenna are arguably better performing antennas than the J-pole, or Slim Jim. Ground plane antennas are compact and should have a flexible whip. These are needed for vehicle applications, yet are not as easy to make, or the best overall good choice for the home builder. If an expedient vehicle antenna is needed, I suggest looking up ‘how-to’ videos on a ‘cantenna’. One can also re-tune old magnetic mount CB antennas to any other VHF/UHF frequency, and can be found for a very low cost at yard sales. I have acquired a pile over the years.
If the goal is durability, and an ability to use a wide choice of suitable materials, J-poles can be made from just about any conductive material. Having built many different antennas types, and from many different materials that were comprised of steel, copper and aluminum, copper is my favorite. Unfortunately, copper is now expensive. But fortunately, the latest pile of copper was almost free to me. Last summer, I traded one antenna for a huge pile of new-condition copper pipe. One can find scrap copper, however, with hyper price inflation soon to be at our door, even scrap copper will get expensive. And so will be the fittings, yet if one is building just a few antennas, it is still worth it to buy it new as it a good way to get started. Eventually, we can learn to make J-poles from many different kinds of scrap materials, but it best to begin with standard 1/2″ ridge copper pipe, and fittings, and use an online J-pole/Slim Jim calculator to obtain the pipe lengths.
The copper pipe J-pole has a major advantage for the novice in that, if a mistake is made, it can easily be corrected by soldering a longer piece in, or cutting the radiator down until it is resonant. If aluminum is used, correcting a mistake is not possible by soldering in a new section. With time, the builder will obtain the necessary skills, and will avoid making mistakes, and thereby open up the possibility of using aluminum or steel that is not forgiving to work with. If mild steel is used, the area where the cable wire attaches by a hose clamps, needs to be painted to prevent rust. Inexpensive galvanized EMT tubing does not rust, and would be a good choice of materials. Tubing of any material kind does not need fittings to create the U-section that makes the pipe in to a ‘J’ configuration. It can be bent if enough skill is involved.
Home Made Directional Antennas
Once we have mastered one antenna type, we can then apply our newly developed skills to other antennas. While the yagi antenna is popular, or a well-known directional antenna, known for it’s high gain, I believe the more practical choice for the home builder is the Moxon. I would also suggest a 6 element OWA (Optimized Wideband Antenna) yagi. Look up the detailed discussion and design by L.B. Cebik. Both have exceptional broad bandwidths and high front to back ratios, and are 50 Ohm direct connect that make it easier to build. Horizontally polarizing antennas, be it a J-pole, or a directional antenna, great decreases the likelihood of being heard to the rear. And the gain of the antenna increases the signal output to the front. For example, the modest gain of the moxon antenna of around 5.75 Dbi (Decibels for an Isotropic radiator. Dbi should not confused with Dbd.) can increase the effective radiated power of a 4 watt transceiver to upwards of 9 watts. The 1/2” copper pipe Moxons are outstanding as these have an exceptionally broad bandwidth if properly constructed.
Tuned for 152Mhz, the harmonic frequencies that can also be used to transmit on this antenna can be 462-465Mhz. This means that you can talk on MURS, and GMRS with the same antenna. However, it would not radiate in the same way on the harmonically resonant frequencies of 462-465 in the same advantageous, and well-documented way that it does at the design frequency of 152 Mhz. Same with the 2-meter variety, 70cm, above 430Mhz can be used if the center frequency is 146 Mhz. Different materials and techniques make each antenna unique, so it is difficult to say exactly how your antenna will perform. If the design frequency (center frequency) is 149.5 Mhz, if built with precision, the antenna can cover 144-156 Mhz with an SWR of less than 2:1 to 1. This means we need only one antenna instead of two antennas and two sets of cables.
A Moxon is ideal in terms of ease to build, exceptionally wide bandwidth, broad area coverage to the front, 144 degrees plus at closer ranges when vertically polarized. When horizontally polarized, the RF footprint shrinks to only 100 degrees, closer to that of a 3 element yagi. More important in my book, is that the Moxon antenna it has a very high front to back (F/B ratio) ratio that blocks the transmission to the rear. The F/B ratio is more important than it’s gain of only 5.75Dbi. Its modest gain is actually an advantage in my book as well, if the purpose of containing the signal within an AO is desired. The F/B ratio is extraordinary 18Dbd at the edges, and up to 40Dbd at the null (center) if transmission is on the design frequency. An average F/B might be 30Dbd, but I’ll use the lowest measurement, 18Dbd. Rotate the antenna so that it is horizontally polarized, and the attenuation is increased about 10 to 20Dbd. 20Dbd + 18Dbd (F/B) = 28 to 38Dbd total attenuation. A 4-watt transmitter would have an ERP given a gain of 5.75Dbi, of about 9.16 watt ERP (Effective Radiated Power) if there is no coaxial cable line loss.
If the signal that is transmitted to the rear is attenuated by 38Dbd, then the ERP of the signal out the back would be around 0.001 watts. In reality, however, this is ideal situation, yet the signal can bounce off reflective objects and change polarization and direction, so that in actuality, more signal goes to the rear than the math suggests. Yet the math is good for comparative purposes and the Moxon antenna compares well with 5 element yagis that have a gain of 10 to 11Dbi and a similar F/B ratio. And Moxons require less time and material to construct.
If one used only 1 watt through a Moxon, the ERP out the front would by only around 2 watts after 25 feet of RG8x line loss is considered. That is just enough to be heard out the front through heavily forest terrain and over small hills, but nearly zero signal goes out the back. This is ideal. Used conjunction with a brevity code, one reduces the audience size and the opportunity to be overheard. These low-tech means are not ideal but do work in the real world, and they are sustainable technologies. I cannot build a high-tech radio, but I can build a low-tech directional antenna. Moxon antennas can be made for UHF frequencies to HF. And they can be built to be very lightweight and collapsible from UHF to HF frequencies. Or they can be over-built to be nearly indestructible.
Another useful advantage and reason to build a high gain antenna of any type, is the increased ability to hear weak signals from a low-powered network. It might be possible in your terrain to use a handheld on low power of 1 watt to talk, and a high gain antenna to listen to that weak signal. This means that a weak signal can be heard over greater distances, distances that are normally not possible for a low-powered network. For example, I can clearly hear very weak FRS radios transmitting with no more than 1/2 watt from distances of up to 10 miles away if I am using a good antenna. Most receivers (scanners) will not have such an antenna and will not hear very low-power radios. This means one can have the benefit of more powerful transmissions and extended ranges, and the security of low-power transceivers. Yeasu and other good transceivers offer adjustable outputs for each power setting. It is easy to reduce the power out to a minimum threshold needed to compete a communications circuit. And these radios have better sensitivity than Baofengs that are a bit “deaf”.
Conclusion
The science is important, but the Art of Guerilla Radio is more important. It can not be taught adequately well. It must be practiced. Creative problem solving is the heart of it. There is no way I can share all of the secrets. However, we can get started.
With practice, a Slim Jim or J-pole, or other simple and expedient antennas can be knocked together quickly and with minimal cost. The last batch I made recently used .75″ diameter scrap aluminum tent poles and a few wire ties. These are excellent performing antennas with a material cost under $1. These are almost disposable antennas, yet they are durable enough. But why go to the trouble? Because for one or other reasons, it may not be possible in the future to access commercially available antennas, and there might be a need for a low power radio network to service a community for the purpose of mutual defense, and to encourage a local economy. And for the simple fact that people will be thirsty for information and a sense of community during a time when extreme poverty and hunger exist.
Once cell phones become difficult to afford or unavailable, the need for radio communications will become obvious and in demand. Sadly radio is not as much appreciated as it needs to be. Amateur radio operators can be central to a community, but I would also endeavor to learn how to do the opposite of what Hams are geared to do, and that is to learn how to talk to a select few stations as possible, rather than to talk to as many station as possible, as far away as possible.