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amateur radio - Hackaday

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The Low-Down on Long-Wave: Unlicensed Experimental Radio

Posted: 19 Oct 2021 07:00 AM PDT https://hackaday.com/2021/10/19/the-low-down-on-long-wave-unlicensed-experimental-radio/


In the 125 years since Marconi made his first radio transmissions, the
spectrum has been divvied up into ranges and bands, most of which are
reserved for governments and large telecom companies. Amidst all of the corporate greed, the little guys managed to carve out their own small
corner of the spectrum, with the help of organizations like the American
Radio Relay League (ARRL). Since 1914, the ARRL has represented the
interests of us amateur radio enthusiasts and helped to protect the bands
set aside for amateur use. To actually take advantage of the wonderful opportunity to transmit on these bands, you need a license, issued by the
FCC. The licenses really arent hard to get, and you should get one, but
what if you dont feel like taking a test? Or if youre just too impatient?

Well, fear not because theres some space on the radio spectrum for you, too.

Welcome to the wonderful world of (legal!) unlicensed radio
experimentation, where anything goes. Okay, not anything  but the possibilities are wide open. There are a few experimental radio bands,
known as LowFER, MedFER, and HiFER where anyone is welcome to play around.
And of the three, LowFER seems the most promising.
Gettin The Band Back Together

Before we dive into what the LowFER, MedFER, and HiFER bands actually are,
its worth noting that these rules apply in the US only. Thats not to say
that these bands are illegal elsewhere, but be sure to check your local frequency allocations before firing up a transmitter.
Ground wave radio propagation along the surface of the Earth. Courtesy of Electronics-Notes.com

LowFER, as the name would suggest, contains the lowest frequency range of
the three, falling between 160 kHz and 190 kHz, with a whopping wavelength
of around one mile. Also known as the 1750-meter band, this frequency range
is well-suited for long transmission paths through ground wave propagation,
a mode in which the radio signals move across the surface of the earth.
This can easily carry even low-power signals hundreds of miles, and occasionally through some atmospheric black magic, signals have been known
to travel thousands of miles. These ground wave signals also travel well
across bodies of water, especially salt water.

MedFER is the medium frequency experimental band, specifically running from
510 kHz to 1,705 kHz. Now that range may sound similar, and it should
because its also known as the AM Broadcast band! Thats right, you can
listen in on this one with your old AM radio. Theres a catch though
amateur experimenters are limited to 0.1 W of transmit power, and can only
use a three-meter long antenna. While thats fine for playing around, theres little chance of being heard very far away over the 500 W  professional stations with massive antennas that dominate the band.

And then theres HiFER, the high-frequency experimental band. Much narrower
than the others at only 14 kHz wide, it sits centered on 13.56 MHz. This
band is commonly used for many RFID applications, including keycards,
public transportation payments, and Nintendo Amiibo. Experimentation on
this band is limited to extremely low power levels, and at such power
levels signals only travel a few inches, which is perfect for RFID.

While theres a lot that can be done on any of these bands, LowFER seems to
be the one that yields itself to some serious fun. MidFER and HiFER both restrict power used so low that youre not reaching outside of your house,
or even arms length, respectively.
Low Frequencies, High Expectations

Like the other bands, LowFER does have some restrictions but theyre much
less limiting. First and foremost, the power into the last change of the transmitter cant exceed 1 W. Thats still fairly low power, but there are
some digital modes, such as WSPR, that are known to propagate around the
world at 1 W on some frequencies. Antenna lengths are also limited to 15
meters which seems awfully short compared to the nearly-two-kilometer wavelength. Generally, the length of such a wire antenna should be tuned to
a fraction of a wavelength 1, ½, ¼, etc. for maximum efficiency. In this case, antenna length also includes the transmission line between the radio
and the antenna. For this reason, its common to connect antennas directly
to LowFER radios to maximize the radiating length of the antenna.

As you may imagine, because the frequencies were dealing with here are so
low, there are few commercially available solutions that let you get
on-the-air with LowFER but when has that ever stopped the hacker and
amateur radio communities? Even with these limitations, weve seen some wonderful kHz-range projects, like this Altoids Tin Beacon and this Arduino-based transmitter. If you want to start out by listening in, there
are a number of beacons on the air right now.

Bandwidth is obviously an issue down low, so LowFER applications probably
want a microcontroller- or computer-based solution driving them, so theres nothing to stop you from keeping the link running 24/7. The long antennas required also favor fixed operation. Intra-Hackerspace low-bitrate data networks?
How Low Can You Go?

So, now its your turn. What will you do with LowFER? Build a tiny
transmitter and try to talk to a far-away friend? Send some waterfall art
out into the æther, hoping some distant hacker sees it? Maybe even just
engage in some good-old fashion CW. Although LowFER has been around for a while, we feel that theres still a ton of untapped potential here for some crazy hacker fun. Just make sure to check (and obey!) your local laws, and
tell us about anything awesome you do!

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