Part of the joy I get as an instructor and consultant is the diverse and quality interactions I have with students. Everything from their thoughts on what makes a good homestead or their successes as preppers to their favorite shortwave stations, its a blessed perspective that I get from everyone and something I like to be able to pass on to everyone else. In one of the recent classes a very brief conversation ensued just on the utility of shortwave and how these days its becoming more challenging to listen into good stations, both because of the number of stations going off the air and the sun cycle approaching its minimum, limiting propagation and increasing the signal to noise ratio. Reception can be tough, and just like how we want to ring the most efficiency possible out of a transmitting antenna, we need to do the same for reception. We do this through building a solid receiving antenna, and the best designs are just a tad different than the standard dipole, end-fed or vertical that most are used to. The two most popular ones, because they work, are the Beverage and the Ground or Grasswire Loop.
There’s a ton of reasons for building a good receiving antenna- from improved reception of distant shortwave and AM broadcast stations to digging out weak signal transmitters, the ability to listen and even pull out good quality signal is very important for the prepper and homesteader looking for quality information from a wide variety of sources. On the clandestine monitoring end, a certain amount of information can be inferred from the various utility stations on the air; anything from the numbers stations which populate the HF waves to the USAF Global HF net. Although many might wonder just what the value would be in listening to these is if we don’t know what’s actually being said, the number of times these stations go on the air and the amount of traffic can give us an idea that we might want to pay attention to the news, as something is going on or about to go on. But operationally, such as communicating over a region, having a good receiving antenna is important. From a transmitting standpoint a common clandestine weak signal transmitting method is to send a burst message on one frequency with a tiny amount of power and receive a response on another with the same type of weak signal, both times in an attempt to mitigate the direction finding (DF) threat. Having a good receiving antenna running to a dedicated communications receiver, such as the Radio Shack DX-394 pictured above, some of the higher-end SDRs or any receiver made by Icom or AOR, becomes an important tool to the Underground when establishing regional communications even when the solar cycle is not cooperating.
There’s two relatively simple antenna types that can be built at home and on the cheap- the Beverage (do yourself a favor and gloss over articles part I & II) and the Ground or Grasswire Loop. The Beverage is an excellent option for low noise and relative simplicity; the problem is that it requires a large space to be erected which most folks living under the thumb of HOAs cannot accommodate, and its peak reception is directional to end-fire of the antenna. In order to get 360 degree coverage, you’d need two. And maybe you don’t need that- which is something that requires preplanning- but then again maybe you do. A way to overcome this is through building the other option- the ground loop, also known as a grasswire loop, which has a much broader reception lobe.
Many of you who’ve read mine and various other QRP and NVIS articles may recognize the term grasswire– it gets its name, simply enough, from being a run of wire stretched out either just above the grass or laid on the ground itself. The advantage of this design is that it is very low noise due to its relatively high loss- meaning that it’s not a transmitting antenna by any means but can listen very well when paired with a good receiver. When used as a transmitting antenna, it would have great reflectivity from the ground which is an asset for working local NVIS propagation but loses quite a bit of signal (also known as negative gain) for going longer distances- possibly another asset for the same clandestine communications methods.
Grasswire Loops are relatively simple to build- all you really need is a run of wire, four insulators and a balun, which you can build yourself as well as purchase. And while the diagram shows 70 feet of wire, you can make the sides shorter as needed to suit your space requirement. Loop antennas as a rule should not be longer than one electrical wavelength (936/frequency= One Full Wavelength Length in Feet). And since receiving antennas are low noise by design, 75 Ohm coax that’s used for cable TV and found pretty much everywhere is perfect. Keep in mind that these normally have an F-Type connector. All of the components can be found in the local hardware store and built in a couple of hours- and the ability to build is a great skill to have when buying readily made equipment might not be an option.
Experiment with one over the weekend and find out what you can do. Better yet, inquire about an upcoming signals intelligence class I’m putting together where we might just build one, along with training on a lot of other neat techniques.
If you want to learn more about communications for preppers and survivalists for both the small unit and across a region off the grid, consider scheduling a slot for the RTO Course. It is a class unlike anything offered anywhere else. Open Enrollment dates for the Summer and Fall of 2018 will be scheduled soon. I also am willing to travel for private groups. Feel free to email me at [email protected] for more details.
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