Article by Popeye
HF radio (High Frequency, also known as short-wave radio) is the handiest tool we have available for regional and national communication that is independent of commercial infrastructure. Cell phones and internet are amazing, yet they are more delicate than most people imagine and their users are easily tracked and exploited by governments and other criminals. Also, it has been demonstrated that commercial communication infrastructure can become so over-crowded or damaged during natural and man-made disasters, that it becomes unreliable or totally ineffective. This is where HF radio comes in: if you can power your radio and erect an effective antenna, then you can maintain communications when all around you have no capability. Notice that I say “effective” not ‘perfect’: impractical ‘perfect’ antennas are never a bargain.
High grade radio equipment and communications software for personal computers have never been more available to the general public. The ham radio station of today would have been government ‘spook gear’ not very long ago. Tiny, reliable transceivers combined with tablet computers, give us the ability to communicate using text, images ( and if necessary ) encryption as well as the very common SSB voice. The only thing lacking for many people is the ability to erect an effective antenna. I’ve had to deal with that lately myself, as we’ve moved from a house in the country with 110′ foot trees, into an HOA (read: “communist controlled”) community just outside of a small city. I like it here, but the “NO HAM RADIO ANTENNAS ALLOWED…”(OR CLOTHES LINES & ETC.) is a pain.
For the bands below 10 MHZ, a horizontal wire, zig-zagged through the house works well for local and regional nets, covering the several surrounding States quite effectively, even at low power. However, on the higher HF bands, my signal to more distant radio friends had inconsistent results. You see, a low, horizontal wire is great for comms out a few hundred miles (see: NVIS) , but its transmitted signal is focused mostly UP; it’s like bouncing a ball off the ceiling above your head – it comes down near you (or on your own head – Ouch!). However, when your goes almost straight-up to the radio ‘ceiling’ called the ionosphere and steeply back down back down, it does not go very far – rarely more than several hundred miles (though there are exceptions). My low wire in the house is rarely heard past 1,500 miles.
HF radio operations in the woods is generally as simple as erecting a dipole or other wire antenna as high and in the clear as necessary. Out there, ‘the sky is the limit’. However, in places where you do not want others to know that you have radio communications capability, putting up a ‘sky wire’ would likely bring unwanted attention. You might be in a Five Start hotel in Switzerland, a grass hut in Swaziland or maybe in your apartment in Sheboygan and decide that operating a clandestine radio station is necessary.. There are many antennas and methods for this, but in this (series?) of articles, I’ll focus on the (drum roll please …)
Small, but Mighty:
The Small Transmitting Loop Antenna
For those with no trees, little room, maybe a patch of grass, or a deck or a sliding glass door where you can erect an antenna and only temporarily, for the bands above 7 MHz, I’d suggest an antenna commonly called a “magnetic loop”. Without getting into the technical mumbo-jumbo, radio signals are electro-magnetic waves. Most antennas capture the electrical part of the electro-magnetic wave but require a lot of room. As an example: a dipole antenna for the twenty meter band is approximately 32 feet end -to-end. However, you can use a magnetic loop antenna that is only 3 feet across yet cab be very effective, sometimes even MORE effective than the wire, when you have limited space! For this test, I operated from INSIDE of the house. Naturally, outside and clear of metal objects would be best.
How effective is a three foot magnetic loop antenna on 20 meters?
Have a look.
For these experiments, to determine whether a 3 foot diameter magnetic loop would does what the calculations SAY that it will do, I bought a very popular ‘AlexLoop and set it up inside of my kitchen in Utah. As you can see in the map above, using just 5 Watts, my Morse code signal was readable all over the USA as reported by the reverse beacon network. This means that my handsent code was strong enough to be reliably copied by the computers attached to the reverse beacon network. Generally, humans copy hand sent code even better than computers. Digital modes like we use for AmRRON digital nets would have similar (or better) results. This proves that my little, battery powered signal was quite readable in at least the above depicted locations.
“I kinna violate the laws of physics, Capitan!
But, Ah kin BEND’em a wee-bit!”
– Scotty, Chief Engineer, USS Enterprise
The 3 foot diameter magnetic loop antenna operates most efficiently on the HIGHER ham bands. The small loop is over 90% efficient on the 28 MHz, but only 13% efficient at 7 MHz. To be efficient 7 MHz ( which we commonly use for regional coverage ) and still be useful on 14 MHz, the AlexLoop would need a diameter of a bit over 5 feet: it’s a matter of physics. However, nobody makes a commercially available, five foot diameter antenna, made to be rolled-up and transported, so back to The AlexLoop!
Rather than to repeat what has already been written about the AlexLoop, here is the website:
Pros of the AlexLoop Walkham antenna
Covers 7-29 MHz
Is made to fit into a NICE, stiffened cloth carrying case.
Can be set-up or stowed for transport in 4 minutes.
Available from GigaParts USA or from AlexLoop in Brazil.
Works VERY well for communication over 1,000 miles on high bands.
Is expensive. Mine cost almost $400 delivered.
Power limit is ten watts CW & Digital / 20 Watts SSB voice.
Does not have an SWR meter built-in.
Only 13% efficient on 7 MHz band.
Not very efficient (but usable) for 7 MHz regional communication.
Summary: Small, magnetic loops have very useful capabilities for operating in limited space and for keeping a low profile. They can be AMAZINGLY EFFICIENT and are commercially available, though rather expensive, usually $300 to $400. Different companies often have different approaches to design, packaging and materials. Now that we’ve covered the basics of how well a small, magnetic loop can perform on the higher HF bands and some of their limitations, I’d like to do scientific testing from places like through the window of a hotel room, out-buildings in a rural area, in trees and from some of our mountains, here in the West to run comparative testing of received signal strengths at distant stations, form factors, ease of use & etc. However, – and this might AMAZE you – I am not a bazillionaire, and sold some other radio items to test this one loop, so that I would know whether magnetic loop antennas can ‘match their math’ which they do! …) . I know that there is also an AlphaLoop, a few versions of the MFJ high power capable loop and likely more. However, it is quite evident that a small magnetic loop, if properly designed and constructed, can produce excellent results; converting your transmitters’ power into radiated signal very efficiently. Some designs are very portable, others are rigid, designed for ‘transportable’ rather than ‘portable’ use. The AlexLoop is actually designed to use while walking, though it’s a bit tiring to do so.
I designed and am currently building a magloop antenna capable of handling 150 Watts continuously. It is larger than the AlexLoop so that it’s much more efficient on the lower ham bands.
I have dreams for an even LARGER magloop to operate on 80 meters and have worked out a way to place it outside, hidden in plain sight –
It’s My ‘Religious Right’
Hertzian Shaman of Northern Utahistan!
( You HAVE heard of the ‘Religious Right” – yes? )
– a little extra –
A quick discourse of hints & kinks on how to want/need to operate ‘clandestine’ when not (officially) at war.
(see definition for “COMMUNISM” ) where anon bureaucrats tell you that you can NOT have a radio antenna. I interpret this a meaning that they do not want me to let them SEE a ham radio antenna and that what they cannot see, will not offend their communist eyes. For the bands 10 MHz and above, I use my small, magnetic loop, inside of my house in northern Utah and it has worked rather well with my sked partner in the far distant south/east of the United States. The signal on high bands was actually better using the loop, rather than with my inside wire, probably because of the better (lower) signal take-off angle from the magnetic loop. That’s 2,500 miles, 5 Watts CW (Morse code).
When traveling, most hotels in what remains of these United States have windows which do not open, so putting a wire-out-the-window (the ‘WOW’ antenna) is not going to happen, even in the dead of night. This “ILLEGAL TO OPEN HOTEL WINDOWS” is especially prevalent in eastern cities. (Note: in The West, we open the window anytime we feel like it, because we are armed and any criminals entering via the window will likely leave via the front door – on a gurney – but that’s not on-topic.) The magnetic loop can fit into its small travel case and be put into your luggage with a small HF radio, thus undetectable because it all fits inside of your normal luggage.
I always choose an upstairs room, top floor if available, with an outside wall/window in the direction of my scheduled radio contact. If my ‘Mother’ station is East or West of me, I tell the person assigning the room that I love sunrises or sunsets and so I want a room on that side of the hotel. If I need a southern exposure, as an adopted Southerner, I can protest the invasion of my adopted homeland by Yankee scalawags by sleeping soundly on the southern side of any building I enter. If you indeed ARE a Yankee Scalawag, just tell them that invading the south is an old habit and you’ll invade that side of their hotel during your visit, thank-you-very-much. (best to say this ABOVE the Mason-Dixon line).
If the North side is needed , you might need to be more creative. Wear a tie-die sarong, (even if you’re male) , bug-out your eyes and say the following:
“I MUST align the 7 chakra life energy hubs in my temporal abode with the north star each night, or suffer terrible night sweats – do YOU have terrible night sweats? Here, I will make some herbal tea for you, made from organic peat moss from MY guru; Hyram P. Maximanunda of Uzbekistan. It’s rich in the mineral gannite, which -everyone knows – grounds-out ALL negative energy within 37 furlongs – precisely. I testify to you that if you drink this tea while facing the great pyramid at Giza, that you will have a perfectly sound and calm mind, just like mine!”…
They’ll give any room you want, just to get rid of you.
Once in the room, electronic noise will be your biggest enemy. To reduce you electrical noise in the radio receiver, unplug the TV and probably the cable box too (do it anyway: TV is called “PROGRAMMING” for a reason). Do NOT use any phone, laptop or other battery chargers during your radio use. These devices often create a LOT of electrical noise. In my experience, hotel telephones, alarm clocks and “ENERGY EFFICIENT LIGHTS” & etc. have been very noisy across the HF radio spectrum. Test your reception by unplugging them WHILE YOU LISTEN ON YOUR SKED FREQUENCY. It has almost always improved my radio reception. Other culprits are electric blankets, some thermostats, florescent lighting.
Now that you’re sitting in your 21st century room, feeling like a 12th century monk with no ‘modern conveniences , (ha ha) you’re ready to put on your headphones/earbuds and make your contact.