Scanning the Spectrum of "Weird Wireless"

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WirelessThere are hundreds of different types of wireless applications. We all use the familiar mainstream wireless technologies like AM and FM radio, Wi-Fi, Bluetooth, and cellular. However, there are many other unusual and less-well-known wireless types. I call them “weird wireless.” I don’t mean it in a derogatory way—just that these technologies are different and out of the ordinary. Maybe you have heard of some of these, and maybe not. Here is a short list for your distraction.

WWVB 60 kHz

WWVB is the National Institute of Standards and Technology’s (NIST) time broadcasting station in Colorado. It transmits digital time signals based on atomic clock precision (<1 part in 1012 error) to synchronize clocks across the U.S. Its carrier operating frequency is 60 kHz (yes, 60 kHz), using 70 kW of effective radiated power (ERP) from its huge antenna array. The digital time codes are sent at 1b/s (one bit per second) using a combination of amplitude and phase modulation. I have an “atomic” watch with a WWVB receiver, and the clock in my home weather station is synced to WWVB.

Digital Radio Mondiale

Digital Radio Mondiale (DRM) is an effort to bring digital modulation to international short-wave broadcasting (5 to 26 MHz range), bringing it into the 21st Century. The goal is to improve upon the quality and reliability offered by the standard AM broadcast methods still used today. DRM uses MPEG audio compression to squeeze more fidelity into the traditional narrow AM 9 kHz or 10 kHz channels. Modulation is coded OFDM with QAM. Bit rates are in the 6.1 kb/s to 38.4 kb/s range. A special DRM receiver is needed.

HD Radio

HD Radio is the U.S.’s digital broadcast radio standard. It transmits a compressed audio signal using OFDM that overlays the normal analog signal on the standard AM or FM frequencies. Most FM and some AM stations have implemented it. HD Radio has been around for over a decade, but few consumers seem to know about it. It does generally improve audio quality and mitigates noise and fading. A special receiver is needed. Some car radios incorporate it.

Magnetic Induction

Magnetic induction wireless is just transformer action. And I am not talking about wireless battery charging, here. The transmitter generates a magnetic field around a primary coil or antenna. The magnetic field is picked up by multiple secondary windings or receiving antennas. Audio can be transmitted directly like this without a carrier. Such techniques have been used to send audio into a theater to special receivers for the hearing-impaired. A version called near-field magnetic induction (NFMI) uses the 13.56 MHz ISM unlicensed frequency to transmit compressed audio for ear buds and hearing aids. The near field of a radio signal is mostly the magnetic field, whereas the far field is the electric and magnetic fields together. The near-field range is severely limited to dozens of feet, max. A popular version is near-field communications (NFC) that is now widely used in cell phones for making payments.

Impulse UWB

Ultrawideband (UWB) is generally well known in its multicarrier format that uses 528 MHz wide OFDM signals in the 3.1 to 10.7 GHz range. It is used in some PCs, laptops, docking stations, and cameras to transmit data at speeds to 480 Mb/s. Range is limited a few meters, so it is not widely used.

Another version of UWB called impulse radio (IR-UWB) uses uniquely shaped short impulses and a form of PSK to transmit data. No carrier is used. The impulses create a very broad bandwidth signal (> 500 MHz). The very low power demanded by the FCC keeps the signal from interfering with other services, but a special coherent receiver can pick the signal out of the noise. Transmissions are very secure. IR-UWB is used for data transmission, ranging measurements, and location services.

PSK31

PSK31 is a digital transmission mode used by amateur radio operators. It uses a PC keyboard that translates keystrokes into a unique binary code, which then uses binary phase shift keying to modulate the carrier. PSK31 uses the sound card capability of the PC and software to handle all of the translations for both sender and receiver. The data rate is 31.25 b/s. It is very slow but only uses 100 Hz of bandwidth, making it possible to transmit data in the high frequency (3-30 MHz) ham bands where channels are usually less than 4kHz. The signal is easily recovered in noise, making it great for low-power (QRP) operation.

RFID Tags

You have no doubt heard of radio frequency identification (RFID). Special coded radio tags are attached to items to identify, inventory, and locate them. What is unique is how the tags work. With no DC power of their own, the tags receive a strong RF signal from a device called a reader. That signal is then rectified and filtered inside that tag chip into a small DC that powers up the chip. The tag then transmits its internal code back to the reader using a form of AM. Range is less than a meter.

Single-Chip Radar

Yes, a whole radar system in one IC. Most are of the continuous-wave (CW) type, operating in the 24-GHz or 76-79 GHz bands. They are now widely used for distance sensing in automatic braking, cruise control, and blindspot detection in new vehicles. They play a major role in self-driving vehicles. One application is liquid-level detection in a tank. Low cost will allow these chips to find other uses.

Miscellaneous

Here are a few other oddball-but-patented schemes that have yet to be adopted for anything.

  • Ultranarrowband, also known as very minimum shift keying (VMSK), is an unusual technique that has been debated for years. It uses zero group delay filters to minimize bandwidth needs for high-speed data transmission. It has been said that the technique violates Shannon’s channel capacity rules.
  • Sequential null wave is another modulation scheme that cancels sidebands to reduce the bandwidth for high-speed data transmission.
  • Cambridge Consultants recently announced an all-digital radio transmitter that sends the serial data bit stream directly to the antenna. No details are available.

Let me know if you hear of any other weird wireless methods.

Discuss this Blog Entry 12

on Sep 28, 2016

LiFi? (You know, the white light spectrum...) It seems to be really getting popular in Europe. pureLiFi seems to be leading the charge.

on Sep 28, 2016

In the 70's through the early 00's, I did a lot of shortwave broadcast listening. I am familiar with the efforts of DRM. But the problem has been that a commercial receiver for DRM transmission was never made available. There was software you could get for a computer that then had to be connected to a traditional AM shortwave receiver, but that was useful only for technically oriented people, not a general audience. Meanwhile, the amount of spectrum pollution from 3 to 30MHz from harmonics and other spurious emissions combining from all these digital device, SMPS's, etc., has all but obliterated reception of shortwave signals. Sadly, this unique part of the radio spectrum, the only one where a modest power signal can have global coverage, has been virtually wiped out by interference from other technologies.

on Sep 28, 2016

As an amateur radio operator since 1958, I can sympathize with pjgeneva. Noise levels in, even suburban residential areas, has steadily increased through the years while Sun spot activities have slumped. That said, modern equipment and operating techniques combined with plain old persistence still makes HF radio a fun hobby. The low power consumption and small size of equipment makes "Field Radio" easy to do from less noisy locations, too.

I was pleased to see PSK31 mentioned. It is an amazing mode to operate. With its ability to dig out a signal that is inaudible, it allows world wide operation with a very low power transmitter. I'd like to point out, too, that it is only one of many digital modes available to hams nowadays. Here is a great page about it: hfradio.org.uk/html/digital_modes.html

73 K9LJB

on Sep 28, 2016

circular polarisation is not only available for light but works in a quite similar fashion for mostly straigt (non-reflected, non-multi-path-transmission) propagating radio waves. whilst in optics some special plate with lambda metrics changing effects (different for x and y axis) is inserted - guess what - for doing radio communications with a sender GHz waves are sent to a one-screw-turn shaped parabolicantenna reflector. the receiver is in principle the same. and the promise is that if you change the steepness of the "screw" shape you will be able to re-use the same frequency without interferring. at least that is the theory whilst indeed the practice has some limitations, that might arise from the mechanical limits imposed by the worsening effects of increased steepness of the screw. at least a zero, +1 and -1 steepness was already very valid in practice. using the concept in other areas than just GHz waves should be possible, at least in theory.

on Sep 28, 2016

Other "weird" ones: spread spectrum, generally, and specifically chirp spread spectrum (used in LoRa).

There are also other ham modes such as WSPR. PSK31 is actually fairly unstrange in that it uses basic phase shift keying and a modulation code that allows for a fairly small number of characters (almost like Baudot encoding for early teletype).

on Sep 28, 2016

While it uses pretty standard radio technology, EME or Earth Moon Earth communication using the moon as a radio wave reflector allows Hams using VHF radios to establish links over distances on earth that would otherwise be next to impossible (Nothing is impossible if you know the right incantations!). Also known as Moon Bounce. Probably not something the average person is aware of so I guess that qualifies as wierd from Lou's definition.

on Sep 28, 2016

Hmmmm, single chip radar ... I wonder how well it would work for sensing water level in a water tank? We are on a well and I have yet to find a good, reliable way to monitor water level.

on Sep 28, 2016

maybe ultrasonic ranging? Depends I guess partially on how much range you need... I think the dispersion after some number of feet will kill the accuracy

on Sep 28, 2016

I grew up in my great grandfather's house. Our well was about 25 feet deep and was brick lined. We measured water level using a length of clothesline rope with a weight on the end. Drop it down until it hit bottom, pull it up and see how much of the rope was wet. Things were simple in the "old days". We had an oak Kellogg crank phone on the wall connected to an 8 party line. Yes, I'm old.. ;-)

on Sep 28, 2016

In WWI, field telephones used a ground return so only one wire was needed, and it was found that enemy troops could set up equipment to listen in using the voltages induced in the ground. British intelligence considered setting up a communication system using that method to send signals from occupied Belgium across the Dutch border by setting up a field telephone for their spy network on the Belgium side and a receiving system in the Netherlands. (Source: Tales of the White Lady)

on Sep 28, 2016

The tank is seven feet deep and I currently use a stick with gallons marked on it. It would be really nice to have a few LEDs light up that told me the approximate water level. A cell phone app indicating gallons would be about as cool as things get!

on Sep 29, 2016

Impulse UWB - I remember when TimeDomain first published on that. They used wavelets with super precise timing to T&R data. Spectrally, it's like the RF version of what Supercontinuum lasers do today. Ultra fast pulses creating ultra wideband output.

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