Homebrew Loop Antenna Brings The Shortwave World To You

Radio may be dead in terms of delivering entertainment, but it’s times like these when the original social network comes into its own. Being able to tune in stations from across the planet to get fresh perspectives on a global event can even be a life saver. You’ll need a good antenna to do that, which is where this homebrew loop antenna for the shortwave radio bands shines.

To be honest, pretty much any chunk of wire will do as an antenna for most shortwave receivers. But not everyone lives somewhere where it’s possible to string up a hundred meters of wire and get a good ground connection, which could make a passive loop antenna like this a good choice. Plus, loops tend to cancel the electrical noise that’s so part of life today, which can make it easier to pull in weak, distant stations.

[Thomas]’s design is based on a length of coaxial cable, which should be stiff enough to give the loop some stability, like a low-loss RG-8 or RG-213. The coax braid and dielectric are exposed at the midpoint of the cable to create a feed point, while the shield and center conductor at the other ends are cross-connected. A 1:1 transformer is wound on a toroid core to connect to the feedpoint; [Thomas] calls it a balun but we tend to think it’s more of an unun, since both the antenna and feedline are unbalanced. He reports good results from the loop across the shortwave band.

The shortwave and ham bands are a treasure trove of information and entertainment just waiting to be explored. Check them out — you might learn something, and you might even stumble across spies doing their thing.

[via RTL-SDR.com]

30 thoughts on “Homebrew Loop Antenna Brings The Shortwave World To You

  1. Loops without an external tuning capacitor are only resonant at one frequency. In this case somewhere around the medium wave band. For other frequencies its more or less a short circuit. Better use a piece of wire with a transformer on a powder iron core. And move it outdoors, this is a recipe for interference.

    Well maybe its better use an antenna like this that actually doesnt amplify with these crappy receivers like airspyHF+ or sdrplay. you might scare the receiver when you attach a real antenna :-)

    1. poor auto translation

      That’s not quite true. The antenna is so strongly attenuated by the extreme low-impedance termination that it gets a very wide bandwidth. Of course, this has the disadvantage that the antenna useful signal is very low. This has to be compensated with an amplifier with a very high gain and extremely low noise.

  2. I thought the Airspy YouLoop is clever. It is two pieces of coax with regular connectors (that can fold flat) and two boxes with connectors and a balun that do the cross-connecting.

    I once built a loop out of a 25 foot piece of 50-pair telephone cable. I cross-connected the ends to make 100 turns and transmitted on 20 KHz using a switching power supply as a transmitter. It went through 150 feet of quartzite in a mine. Also received VLF stations down there.

      1. Started off with a HP boat anchor spectrum analyzer. For really down in the mud signals, a National Instruments A/D card, big bucks. Integrate for a while, FFT and display with Matlab. 20 years ago. I don’t remember the antenna, might have been a “loopstick” wound on a huge chunk of ferrite. We had a “junk box” full of old radars.

  3. I don’t want do discourage anyone from playing with shortwave radio but maybe a disclaimer is necessary here. I’m not sure I would send people to “go learn something” on shortwave radio without one. There are a LOT of cranks.

    I think english language shortwave is the last broadcast medium for a lot of people who have been deplatformed everywhere else. Pizza gate, chem trails, fema death camps and all sorts of false news are commonplace. Bigfoot has a home on shortwave. The irony of using 10s of thousands of watts to claim that Covid19 is caused by RF from 5G networks would be lost on many a shortwave broadcaster.

    Don’t get me wrong, radio is great. Learning to build something that communicates across the globe without depending on some big corporate network is a wonderful thing. Old school AM receivers are so simple a beginner can build one and it’s the only mode that can be received with a no-power required crystal radio. CW is only a little harder to receive but even the transmitters are super simple.

    But maybe one should ask themselves if they are sufficiently educated on current world events and not gullible before looking too hard for information on the shortwave bands. Then, after asking those questions, given the Dunning Kruger effect, maybe reverse the answer.

    1. You left out the endless supply of fire and brimstone and damnation.
      But you can also usually rely on Radio Cuba for some great music.
      And then on to monitor the ham bands where old white guys talk endlessly about the size of their antennas.

    1. Agreed, DX is fun for many. How far away can I hear from? Lots of modes to play with like weather FAX (WEFAX), RTTY, etc as well. And for HAMs, having an antenna that has noise canceling properties is a major plus, especially for those with noise prone verticals.

  4. I’m not an electrical engineer, and I’ve not designed any radio circuits, could someone explain what is the benefit of crossing the conductors opposite from the point where the feed line is taken rather than crossing them at the point where the feed line is taken and saving some work?

  5. I powered up my old Kenwood TS-430S HF transceiver the other day only to discover the neighbors new roof mount solar panel array was pumping out a S9 noise floor. Guess it is time to purchase phase inversion noise cancel device like the Timewave ANC-4 or MFJ equivalent .. or move on to a new hobby.

    1. Under FCC regulations, the solar panel own is REQUIRED to mitigate the noise problem. You don’t have to put up with that.

      I’m thinking of a multi-band design from England designed by a fe)ow years ago called the G5RV that is resonant on almost all amateur bands, and is fairly low noise. A loop has it’s attractions, but power out when transmitting can be a problem if you have major mis-match, a tuner helps, but ain’t that great. Or even a random length wire is great and tunes well. A pal of mine had the power company abandon a transmission line across his property, which he has been using as a random length antenna on HF bands for transmit & receive, works great, and the power company was kind enough to attach his feedline when they severed the wires connection to the power grid. Works great…

      1. It should have read “solar panel owner”.

        If the panels have FCC certification, which they should have, it would be a Class A certification, which must accept any RF interferences. A Class B device, typically TV & radio receivers but includes others, Class B devices are protected and don’t have to accept interference. (Transmitters have a duty to mitigate interference they may cause.)

        It’s better in this rare instance to get a B than an A.

  6. Interesting.

    I’m almost done building a SWL loop from the following link:
    http://www.kr1st.com/swlloop.htm

    This one has a tuning cap which must be tweaked every time the radio tuning is changed.

    The reason I’m trying a loop is that I’m sick of all the EMI from dimmers, switching power supplies, etc. I will try to finish it ASAP to confirm.

  7. It’s hard to explain without diagrams. Look at the line drawing in the “theory” part of the linked instructions. If you trace the path from either side of the transformer into the loop (the yellow and blue lines), you’ll see that they’re symmetrical (eg mirror images of each other) around the ground point (the outer part of the connector to the receiver). This symmetry is part of how this antenna rejects noise.

  8. The Small Vertical Loop Antenna for HF Reception
    Published: 2017-01-13
    Updated: 2019-09-26

    http://www.kk5jy.net/rx-loop/

    Excerpt:

    My original interest in small receiving loops was focused on two-element arrays of such elements, used to form a phased array for improved receive performance on the HF bands. The individual elements of that antenna design were simple wire loops, very small compared to the wavelengths to be received, and not resonated nor tuned for any of the bands where it is used. Such arrays can compete with enormous Beverage antennas many times their size. However, even a single wire loop of this type can be a very effective HF receive antenna for long wavelengths, offering a substantial advantage over many types of transmitting antennas for HF reception. As such, it deserves some additional discussion of its own.

    The lossy, untuned, electrically-small antenna, whether a vertical, loop, or horizontal dipole, turns out to be an excellent transducer for HF skywaves. The efficiency of such an antenna is very low, sometimes on the order of dozens of dB below an isotropic antenna. However, it turns out that the low efficiency actually helps to improve the overall signal-to-noise ratio of received signals. The reasons for this are best discussed in another article, but it should suffice to say that HF operators have known about the desirable properties of lossy receieve antennas since the earliest days of radio, and the Beverage antenna is but one example of a family of antennas that exploit low efficiency to improve the SNR of skywave signals.

    1. Always seemed like I pulled in the whole world when I was a kid with a random coil strung around 4 nails in the wall or the dipole made out of curtain rods. Just had a Citizen brand “all band” knob twiddler.

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