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Ham Radio Articles

Emergency Communications, Alternative Communications, Radio Wave Propagation, Electronics Engineering, Antennas, Field Operations, & More.
smartphone with rtl-sdr dongle & magnetic loop antenna
Lost In The Forest

The story of a man lost deep in the forest at night facing imminent danger. He embarks on a new journey in advanced radio direction finding (fox hunting) & hacking new ways to find his way to safety.

radio station in back of jeep
DoD Crossband Test

A comprehensive guide to the equipment used in a remote location for military communications during the annual DoD crossband test.

portable solar cart for emergency power
Solar Cart

A solar power station for emergency power. This cart powered the entire radio station as well as lighting for 48 hours during a remote field expedition. Directly after the event it was used to jump start a vehicle.

slingshot horizontal dipole antenna
Slingshot Horizontal Dipole Antenna

A dipole antenna that deploys by slingshot between two tall trees.

Lost In The Forest
by KG5EVY

Please read-DISCLAIMER: It is inevitable that I will catch plenty of negative feedback from radio operators the world over for publishing my accounts given the mixed opinions concerning Pofung/Baofeng Corporation. For that reason (and many others), I give the following preemptive statement. – In no way do I recommend the use of ANY radio transmitter without first having an appropriate amount of knowledge in radio frequency theory, as well as testing equipment and methods of evaluating the transmitted signal (into a dummy load). The ARRL has conducted many evaluations of various Pofung/Baofeng transceivers (including models purchased from the American distributor BTECH) with varying results. I myself have a generous pile of these radios and have tested each one thoroughly before use, also with varying results. Quality control as well as the fact that there are a lot of clones out there (some missing filter circuits!) are the two main factors to blame. Others may have the opinion that the fact that they are cheap and of Chinese manufacture are basis for non-use, as well as the fact that most models are capable of transmitting well outside the amateur bands, and are not compliant with geographical laws and regulations. As an operator, the legality of transmitting with these devices is left up to you to insure that you are operating within regulation. In the USA, ham radio operators make up the ONLY service that is authorized by the FCC to transmit using almost all models manufactured by Pofung/Baofeng corporation, and the operator is obligated to ensure that the transmitter is operating within set regulations prior to use. These transceivers have a bad reputation in the community for good reason, however with proper testing and modification (ie. filtering, resonant antennas), these cheap radios can be an excellent option for those with limited funds, or with a need for a capable “beater” radio for use when you just don’t want to risk your $600 Yaesu, Icom, Kenwood, etc. HT. Please be open minded and refrain from supplying negativity.

As an avid outdoorsman, many of my adventures (most in fact) land me in areas without conventional means of communication. More often than not, I rely totally on radio communications. My QTH (location) is in the central Mississippi hill country where the land is densely populated not with humans, but rather with conifers and old growth hardwoods that tower anywhere from 80 to 160 feet above ground level. Being a self reliant “off-grid” homesteader, when I’m not farming, I spend much of my time in the forest as a hunter/gatherer, harvesting what my family needs from the bounty that nature has provided. It is amazing how quickly weather can turn south, and when the clouds come over the canopy, the forest floor turns as black as night. This sometimes makes for a potentially dangerous (possibly even deadly) situation. The forest is teaming with large predators, including (but not limited to) alligators, panthers, bears, venomous snakes, and wolf/coyote hybrids. Weather is not the only concern, getting lost is easy to do anyway. Any RTK (Real Time Kinetic) GNSS (Global Navigation Satellite System) that I am familiar with is completely useless under the dense canopy (especially GPS). A compass is handy, but traversing a strait line is impossible as brambles and other obstructions continuously block the path. Therefore, a wild zigzag course is unavoidable, making navigating with a compass rather arduous. I have a local repeater located at my cabin (for which I am the trustee) which has greatly extended radio communications, but at 300 feet above sea level and a 30’ mast in a location surrounded by trees, there are great limitations with a dual band HT (handheld transceiver), and many times I cannot access the repeater.
 I had been lost twice before with my young sons (once in a heavy storm), but the third time I was alone (thankfully). The mood turned ambivalent in a split second. When I realized I had lost my way, I also realized that I had no means for extraction due to lack of communications. It was dark and the temperature was below freezing. All my senses told me quite sternly that I was being watched from more than one direction. I could hear the faint sound of a footstep at long intervals, and a whistle from a distance. The whistle sound I had heard previously from a confirmed panther (on more than one occasion). Close by, I recognized a vixen (female fox) cry, which sounds like a human baby screaming (not dangerous, but certainly added an audible flare to the situation). I had a green light on my gun, two small flashlights clipped to my pocket, and a headlamp, but definitely not enough battery power to last more than a couple hours combined. I was prepared for the cold and there was zero precipitation, so theoretically I could make it through the night without issue (I felt like staying where I was until dawn was the best coarse of action in order to avoid further deviation), but sitting still without the option of scanning with a light could prove quite hazardous considering the nocturnal predators about. I was in a geographical depression which inhibited communications entirely if I stayed put. My mind turned quite despondent as I pondered the possible actions I could make. I ended up making the decision to stay put until dawn, at least that was my goal. About an hour before first light, under the canopy with very little battery power remaining from all the intermittent scans made thoughout the night, I made the decision to move. I would traverse only a short distance so as to be able to return to my original location, and I would do so in various directions, returning to my original location after each (unsuccessful) short venture. I ended up finding the original path I had used to enter the forest! I felt lucky, and the crazy thing was that I had only deviated by about 20 yards off course by the time I had noticed that I was lost! I made it back to the cabin right at morning twilight, greeted by a waking family that was quite concerned of my whereabouts. I made a pact to step up my game tremendously before my next excursion. What follows is an account of my efforts to reduce the chances of an incident like this being repeated (if there was to be a “next time”, I may not be so lucky).
 Being immersed in radio telecommunications, alternative energy, chemistry, and electronics engineering as habitual hobbies (and necessities given my off-grid lifestyle), I set out to concoct a system with multiple redundancies that could replace GPS/APRS or any other conventional means of tracking location and/or communicating. What I eventually came up with was a combination of different redundancies, all of which lent themselves to my own particular areas of interest and/or expertise. This led me to take up new and interesting aspects of the same hobbies that I was already involved in. This also spawned new ideas for regular everyday life on an off-grid homestead.
 The first step to a solution was simple (at least in concept). I felt really careless. Obviously, I was quite careless in insuring that I was capable of maintaining a line of communications when I got lost. As a radio operator (now humbled), that’s a humongous belittlement to the psyche. The adverse terrain and conditions had left me in a situation that was quite disheartening, but it was my own doing in every way. Next time I would have to be prepared to make contacts despite being under a canopy, in a low lying area, and unable to traverse reliably. A good, solid method for plotting location and relaying voice and/or data traffic to the cabin (and therefore the repeater) was of top priority.
 FOXHUNTING: Foxhunting, in the pretense intended for this account, does not involve horsemen boasting red coats in pursuit of a four legged canine as depicted in many a painting, but rather is a term used for a sport practiced by ham radio operators worldwide. The sport involves using radio direction finding (RDF) equipment to locate hidden or offensive transmitters (or sources of harmful interference in the radio spectrum (RFI)). Equipment used for RDF can be as simple as a handheld transceiver using the operators body to distinguish a null in the received signal (body fade), to sensitive resonant directional or bi-directional antennas (or arrays), and even automated micro-controller based beacon locators that sense signal strength from an array of antennas based on time differential (∆t) of the received signal. This is a sport that I have had an interest in following, but not a practical use for (excluding locating RFI in motor vehicle circuits) until now. What I needed was to be able to triangulate my current location, and/or transmit a beacon from my location that could be plotted by another operator. My two oldest children have an interest in radio and electronics engineering so I felt like I could make the whole thing happen. My oldest son (KG5YEH) was sixteen, and had been a technician class licensee since he was twelve (and was currently studying for general). My eleven year old son had been studying the tech book, playing around on the MURS frequencies, and soldering circuits since ever he could hold a soldering iron. Surely together we could come up with a program that would fit the bill.
 The first experimentation phase with short and long distance foxhunting (RDF) worked like a charm (lucky me!). A beacon transmitted from a baofeng UV-5R using an obsolete tiny mp3 player and some interfacing hardware I soldered up gets a signal out there to track. A home brew magnetic loop antenna for 145.000 MHz allows me to “sniff” out the beacon quite accurately. Being that my location is in the middle of the forest, multipath signals are what I receive, so the signal null is never in the actual direction of the transmitter, but rather it aims me at the strongest point of reflection. This leads me on a wild zigzag trajectory, but that works out quite well given the terrain. With a beacon previously set at my extraction point for a long hike, and one transmitting from the repeater at the cabin, I can triangulate an approximate location using nothing more than my HT and a small magnetic loop antenna (along with a few acquired skills).
 Interfacing: I have been interfacing a smartphone with no sim card (no service) to various Baofeng models for a number of years thanks to some help from a fellow operator, KK6GIP (John Boiles). John supplied a schematic he designed for APRS (automatic position reporting system) to trick the phone into thinking it has a headset attached to it. I simply used the gerber files (files used to print the different layers of a PCB) he designed, and had Osh Park (a community driven, US circuit board manufacturer) custom make me some tiny PCB’S (printed circuit boards). I paid a mere $1.70usd for batches of three boards shipped. This enables encoding and decoding of data transmissions for various uses. SSTV (slow scan television) has been a favorite, but I also use the interface to send email over the air (no internet) using an open source android application called “andflmsg”. This is a lighter version of the same program I use on my Linux computer. The app also allows for text messaging and photo attachments (although I prefer SSTV for pictures). I use two android applications for SSTV. One for encoding, and one for decoding named SSTVencoder and Robot36 respectively. Robot36 runs in the background and files pictures as they are received directly to the gallery. Both SSTVencoder and Robot36 support a formidable list of modes with different characteristics.
 The interface boards are tiny, and populating them with the tiny flea sized SMD (surface mount) components is definitely a task for someone very experienced with soldering. However, I recently was provided gerber files for an adaptation of John’s board that uses discrete (through hole) components. I had Osh Park print me a batch for the kids to build (they are going to use them for a RDF easter egg hunt this year). I prefer the smaller board for portability, but the discrete board is quite small as well and would suit most people just fine (alot easier to populate). There are only five components to solder on either version, three resistors and two capacitors. The only other components needed are a TRRS plug for the phone, and a Kenwood connector for the radio (I use replacement Kenwood mic cords).

aprs boards
(un-populated radio to TRRS interface PCB’s )
aprs cable
(SMD version interface completed and cast in polymer resin)
aprs board cast in polymer resin
(SMD version interface completed and cast in polymer resin)

Beacon: The beacon is quite simple. It is nothing more than a mp3 player plugged into the 3.5mm TRS mic jack on the radio, and VOX (voice activated transmit) turned on in the Baofeng menu options. The only tricky part is getting the VOX set correctly. I may indeed catch some flack here from others as VOX is known to be problematic. I have however had excellent results, but it took a large learning curve to get there. The VOX level must be set sensitive enough to pick up the mp3 players audio signal immediately, yet not so sensitive as to leave a long squelch tail at the end of the transmission (or even to stop transmitting). In the Baofeng menu (or in CHIRP if you are programming with a computer), TDR-AB (dual watch VFO) must be set to “off” so it does not receive a signal on the other VFO (variable frequency oscillator) while transmitting the beacon (by the specs, this should not occur anyway, but it can). The VOX level setting must be played with due to the audio level from the mp3 player (play with that too), as well as varying resistance in the connections. Also, of all the transceivers I have tested, each one has a different “sweet spot”, often drastically different from others of the same model. I use an mp3 player with only one audio file uploaded to it because the beacon will be left unattended, and if something should go astray, I cannot risk transmitting music or some other file (regulations and common etiquette). A smartphone DEFINATELY cannot be left unattended for even a second! My beacon transmits for just under 90 seconds, and repeats every five minutes. I set the TOT (transmit timeout) in the radio settings to 90 seconds to ensure that VOX does not keep transmitting (just a precaution). Anything more would push the radio too much anyway, likely causing it to overheat.
 I created the audio file using Audacity on my Linux machine (I keep multiple files describing different possible situations on my smartphone for field use). The audio file starts off with a 4 second continuous tone to break the squelch on the receiving radio, as well as to make sure VOX on the transmit radio picks up the audio before the message starts transmitting so no information is missed. After the tone, there is a morse ID giving my callsign. Then a computer generated voice identifies with my callsign again, and describes the nature of the transmission, followed by an SSTV image (my callsign is on the picture, along with Swift the fox and David the gnome lost in the forest). Voice as well as morse sign off the transmission, followed by another 4 second tone at the end. To deal with VOX problems (cutting out), I layered a sub-audible white noise track in the background of the audio file. This keeps VOX open without issue throughout the entire transmission, and allows for the VOX setting to be set to a less sensitive setting which avoids other problems. The actual transmission is just under 90 seconds, but my file is exactly 4 minutes 59 seconds. The extra time on the file is computer generated silence so the file can be looped repeatedly and start every 5 minutes, transmitting only 90 seconds of actual audio.

hand held radio beacon with mp3 player
(UV5R connected to obsolete tiny mp3 player via 3.5mm TRS male to male adapter)

Antenna: Designing and building antennas is one of my favorite aspects of the radio hobby. I absolutely love it! My wife may not, but she has yet to attempt to stop me (no TaeKwonDo attacks yet!). I have designed and built homebrew antennas for every situation (that I have thought of yet….), including both repeater antennas, the antenna on my vehicle, and even a 40 meter horizontal dipole that packs easily in my backpack (along with a slingshot, fishing line, paracord, and a lead weight I sand cast myself to shoot lines into the tops of the trees, and stretch the antenna high above ground), plus many more. This venture would require preferably a directional antenna, but most designs, like the yagi, are too bulky. To borrow a term from the Navy, “light is right” for this setup. I don’t want to carry even a backpack. I needed something manageable, and would have to settle on some middle ground. I decided to design a small magnetic loop antenna for the “sniffer” receiving radio that was capable of transmit as well. In theory, magnetic loops are omni-directional, however, they present a fatal flaw that I planned to capitalize on. They display a bi-directional characteristic with an extremely sharp null when directed toward (or directly away from) the source of a signal being received. The antenna will completely blank the receiver when aimed directly at, or directly away from the received signal. This has proven to work quite acceptably in practice, and is quite small, enough so to just leave it on the HT I carry on my belt when thrashing though the brambles. Mathematical calculations proved to be the most difficult aspect of the design phase this time (one calculation changes another, making for a lot of changes throughout the design process, similar to a paradox, but the “loop” did have an end).
 Magnetic loop antennas capable of transmit require a capacitance of a very low value, yet capable of handling an EXTREMELY high voltage. This throws out any of the conventional “store bought” capacitors (ie. electrolytic, ceramic, multi-layer, etc.) excepting an air variable. Air variables are bulky as well as expensive. I had a few that I purchased at a hamfest for next to nothing, but the size (weight) is just too much for my “light is right” attitude. I would have to design and construct my own capacitor to fit the bill, and a fixed plate stator design (aside from being right up my alley) seemed to be the most formidable option. A fixed plate stator capacitor designed for the task could not only be small, but also handle extremely high voltage, and be made from materials most anyone already has.
 Plate area and separation are calculated dependent on the dielectric value between them (ie. various plastics, paper, air, etc.). Don’t tell Uncle Sam, but I like to use coins for plates, and have done so on countless occasions. I have constructed capacitors and batteries using coins and have had nothing less than exemplary results. It seems there is a coin sized to fit the bill for just about any project. Circular plastic pieces from various children’s toys, games, and poker chips work great as a dielectric spacer between coins. One or more dielectric pieces can be sandwiched between coins to facilitate correct spacing, and are easily held together with a teflon machine screw (tapping one of the coins means no need for a nut or washer). The “sandwich” design makes for easy modification (ie. stacking more or less pieces, thicker or thinner pieces, etc.) while testing the antenna with a capacitance tester, VNA (Vector Network Analyzer) or other suitable device. Modifications are often necessary after testing in the “real” world, as mathematical equations give only a “theoretical” depiction of functionality. Simply put, all the math is merely a starting point, but quite necessary nonetheless.

hand held radio with magnetic loop antenna
(UV5R connected to homebrew magnetic loop antenna. Driven element is cast in polymer resin, as is the BNC connector which is adapted to SMA female)

Filter: Filtering of the transmitted signal from the beacon may or may not be necessary (test the transmitted signal into a dummy load to identify spurs and/or harmonics that may be present). One of the transceivers (UV5R) I am using required filtering (the third harmonic exhibited a higher signal strength than did the fundamental frequency!), and a relatively simple tank circuit performs this task quite effectively at 145.000MHz in a suitably compact physical form to boot. Another UV5R that I use for the second beacon required no external filtering (tested). In foxhunting, when close to the beacon transmitter, it is beneficial to have the ability to receive a harmonic (third harmonic in my case), but the harmonic must be attenuated significantly to be of benefit. Switching to the third harmonic of the fundamental frequency (435.000MHz in my case) allows for attenuation without the necessity of carrying an external attenuator in the field, thus enabling less equipment that I have to tote around. Bandpass, high pass, and low pass filters are effective, somewhat complex circuits often implemented for this purpose that have the ability to cover a wide range of frequencies. One particular set frequency is all I need here, so a tank circuit fits the bill just fine.

tank circuit
(Tank circuit filter before casting in polymer resin. Note the fixed plate stator capacitor constructed from two US dimes separated by a plastic coin dielectric from a children’s game.)
tank circuit in polymer resin
(Tank circuit filter cast in polymer resin)

3-2-1 Lift Off: Ensuring that being “out of range” for communications NEVER occurs (an impossibility, but a worthy goal) means increasing the antennas elevation from ground. If I were on a field expedition with my pack, I would slingshot my 40 meter dipole between two tall trees, but I won’t be carrying the pack so I needed another option. Pyrotechnics is one of my favorite pastimes, if you could call it that. Of the many fun endeavors that pyrotechnics has to offer, one of my favorites is the concept of making model rocket engines. I have often aspired to attach a beacon to a model rocket to transmit telemetry back to the ground. This was my first thought that I shot down immediately after thinking it. Fire and conifers don’t go together (actually they do, all too well!), and the last thing I need is a forest fire to add to an emergency situation. I decided to turn to chemistry, and immediately began experimentation with producing hydrogen to launch a weather balloon. Near space weather balloons are launched every day from various locations around the world. The bare minimum effective balloon is all I need, so I set out to determine what exactly was necessary. If I could simply lift the whole transceiver with a pre-programmed beacon playing on a loop, I could avoid carrying any extra radio equipment. Also, the payload would be significantly lighter than a 200’ length of coaxial cable (less weight equals less hydrogen required to lift it).
 The experimentation phase was quite extensive. Creating hydrogen is relatively simple, but constructing the apparatus with the lightest weight and smallest footprint took a lot of effort, as did determining the amounts of the three key ingredients to exacting measurements.
 To produce hydrogen, one must first obtain a vessel to use as the hydrogen reactor. This vessel must be able to handle high heat, and it must be made from a material that is non-reactive (ie. glass or stainless steel). Hydrogen is produced when aluminum is exposed to water (it’s that simple, kinda). Aluminum is similar to copper in the aspect that when exposed to water it corrodes almost instantaneously. The corrosive layer that is formed protects the surface from further contact with water. In order to keep water in contact with the aluminum, a third ingredient is necessary. This is where sodium hydroxide (lye) comes in. Sodium hydroxide continuously eats up the protective layer caused by corrosion. A saturation (the highest amount of a solid that can be dissolved into a liquid) of sodium hydroxide enables the most rapid reaction, but without cooling, the exothermic reaction quickly becomes too hot for a latex balloon. Cooling can be accomplished with a water bath, or by simply submersing the reactor into a generous amount of water. The reaction occurs exponentially more rapidly with increased heat, so if we have to cool the reactor, we are wasting ingredients. I don’t like to waste anything anyway, but when I have to carry it along with me on an expedition, its just not an option. Many experiments were performed to produce the most efficient and effective reaction, but I do not wish to speculate that these ratios would work well in another reactor vessel. The amount of hydrogen needed to lift the transceiver took rigorous testing as well, despite performing an exhausting multitude of mathematical calculations. I eventually determined that lifting the transceiver required too much time to produce the amount of hydrogen needed, and also required more bulk of apparatus than I was willing to carry. A new approach was imminent, and the final decision was to lift a length of 28awg magnet (inductor) wire as an antenna instead.

aluminum can tabs
(Tabs from aluminum cans make great fuel for the reactor)

A stainless steel vodka bottle along with some PVC handy work proved to work well enough, but it does create too much heat for the latex weather balloon if I am not careful with ratios and don’t have a method to cool it down. Going lite on the sodium hydroxide and heavy on the water slows the exothermic reaction down enough to avoid the excessive heat, but takes more time to produce enough hydrogen to lift the antenna. A ditch or puddle with water to partially submerse the reactor vessel in is sometimes necessary. 

stainless steel vodka bottle & PVC pipe
Simple reactor vessel that starts off as a water bottle on the trek. 

A reactor design that promotes a fast reaction and cleaner hydrogen production, that is also less likely to overheat the latex balloon, utilizes two vessels. The first vessel is the reactor, and a tube carries the hydrogen produced to the bottom of the second vessel which is partially filled with water. Once deposited in the bottom of the second vessel, the hydrogen bubbles up through the water and into the balloon. In this process, the hydrogen gas is filtered as well as cooled by the water. This design however, lends itself to a larger expedition where toting more gear is an option.

stainless steel hydrogen reactor assembled
(Reactor vessel with the addition of a “bubbler” vessel to facilitate a faster reaction without melting the balloon)

Filling a 36” diameter balloon takes about 30 minutes, but can take longer if the exothermic reaction has to be cooled too much in order to protect the latex balloon from excessive heat.

hydrogen balloon filling from reactor
 (36” diameter latex weather balloon being filled with hydrogen)

Epoxy Resin: Waterproofing and providing structural integrity to circuits can be accomplished by casting PCB’s, connectors etc. in a polymer resin (epoxy). Envirotex Lite or Watco Super Glaze are the two products I know of that work well. These are marketed as bar top finishes, but have many other uses as well. A monoject 412 syringe or similar (eye dropper type veteranary syringe) is useful for introducing the epoxy to the mold. Molds can be made from a variety of different materials. Aluminum foil, masking tape, pvc pipe, and wood are materials I frequently use. I use a small artist paintbrush to coat the mold with petroleum jelly to aid in release of the finished product. 

KG5EVY is a guest contributor on this site.
copyright KG5EVY

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