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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.

DoD Crossband Test

Annual Event
jeep cj7 with roof mounted solar panel
jeep cj7 solar powered radio station
camp fire

 The United States Department of Defense conducts a 24 hour long test of interoperability once every year on or around Armed Forces Day. This year (2023) the event occurred one week before the recognized holiday. The test is cross-band, with military stations transmitting encrypted data on frequencies designated for that purpose, and receiving or “listening” on frequencies in another band or bands. This test is multi faceted on DoD’s part. DoD simply calls it a test of “interoperability”, which is a term that usually refers to different computer systems or protocols ability to interact with one another. The reason I say that the event is multi faceted is partly due to the nature of these “systems or protocols”.

 DoD itself is the heart of a somewhat vast conglomeration of entities commanded (or commissioned) by the United States Government. It is the largest employer in the world! The Marines, Navy, Army, Air Force, Space Force, etc. are a few most would know about. Together, there are eight “uniformed” services that answer to DoD, most of which would be recognized by the average person, but there are others that don’t wear uniforms and work more behind the scene. Some of these services that work “behind the scene” are extremely vital assets to DoD, and ham radio operators are at the top of that list. DoD has relied on ham radio operators since DoD’s conception. In fact, the technology that they use has come either directly from ham radio, or spawned from experimentations conducted by ham radio operators over the years.

 The test of “interoperability” goes well beyond testing “systems or protocols”, at least if you consider those terms to refer to software or hardware exclusively. It is a test of an operators abilities, and most of all, an operators ability to adapt.

 For all eight uniformed services to have the ability to communicate effectively, each one relies on a multitude of software and hardware assets, as well as skill sets from operators. But for all services, uniformed and not, to communicate and interact together efficiently in real time (and in the real world), some serious effort is required. This is where the annual cross-band test comes into play. This is where operators get to “stretch their legs” and deviate from the standard protocols in which they operate on a day to day basis. Frequencies used for this event are all over the board. Data is encrypted, modes change, protocols change across the spectrum, and stations locations around the world may be “on the go”, generally with quite a few ships of various design implemented as transmitting stations. Its a chance to operate in many areas that would not normally be available for use.

radio station in back of jeep

Most operators who participate in this event operate from their shack using everything they have at their disposal. This may include large antennas or vast arrays, & transmitters capable of transmitting at very high power levels. Multiple computers & electricity from the grid are the norm. After all, this is an extremely difficult event for any operator.

Being an avid outdoorsman & survivalist, I decided to make this a field expedition as well. 

My jeep is set up as a full blown radio station. A complete solar electrical system provides all the electrical energy needed for 24/7 operation without starting the vehicle.

40 meter slingshot dipole antenna
40 meter slingshot dipole antenna

A 40 meter dipole that I constructed for backpack expeditions suits the bill quite well for all of the HF bands when combined with a tuner. This one utilizes a slingshot & a fishing reel to deploy the antenna between two tall trees. A tutorial outlining the construction of this antenna is available on this site.

Several (h)ammo cans I call my MIL-COMM boxes house transceivers with their own integrated long term battery backup, as well as charging ports & charge controllers that can be plugged into any power source. AC, DC, virtually any voltage power source can be directly plugged into the boxes to charge & run the equipment. In the jeep, they are simply plugged into the vehicles electrical system which is producing power from the solar electrical system, & the alternator if the jeep were to be running.

midnite brat solar charge controller

The vehicles solar electrical system charges the jeeps battery & anything else connected to it via the Midnite Brat charge controller. Midnite is a company that I have a lot of experience with & trust. The Brat was chosen for this build because it is waterproof & is more than sufficient to handle the amount power produced.

inrush current protection circuit

The ammo cans themselves boast their own independent solar charge controllers that charge their two series connected 6 volt deer feeder batteries from any source. They control the charge cycle separately from the vehicle even when connected to the vehicles power supply. A circuit utilizing thermistors was designed & constructed to prevent inrush current to these controllers when their power sources are continuously changing origin (like when the vehicle is running or not). The circuit is cast in polymer resin making it water proof. Magnets are cast into the resin as well so it sticks to the side of the metal ammo cans. This setup works quite efficiently.

dipole antenna feed point

The dipole antenna is stretched high between two very large trees with lengths of paracord. The paracords go over one of the highest branches in the trees & then come straight down to ground level, where they are tied to cinder blocks that are hanging off the ground. This allows the trees to blow in the wind without affecting how tight the antenna wire is stretched. This setup worked in high winds & rain without fail. The feed point is anchored to the tee post in the above picture, with the coaxial cable going to the jeep on the ground marked (& held down) by flags.

rtl-sdr dongle

An rtl-sdr dongle makes for an extremely welcome friend while searching for signals across the spectrum. I run various linux distributions as the operating systems on my laptops, & cubic sdr in conjunction with pulse audio for porting & fldigi for decoding make monitoring many frequencies from virtually DC to daylight simultaneously possible. A DC fan is used to keep the dongle cool, as it tends to get off frequency when it gets too hot after heavy use.

hammo cans

All in all, the event was a success! It rained, it was windy, & it was cold at times, but it was a success. All of the various systems that made this happen functioned properly, with minimal problems during the 48 hour adventure in radio. The toughest part (the whole thing was tough) was staying awake for so long, but that is the case in any drill or actual real life operation. I look forward to setting up somewhere else next year, perhaps with a few more tricks!

KG5EVY is a guest contributor on this site.
copyright KG5EVY

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