Fullscreen HTML5Med Res (??MB)HTML4

Digital Radio Modes In part one last month we looked at many of the varied types of digital radio in use today. But we couldn’t fit all of them in . . . so here we’ll continue our discussion of some more digital radio     Part Two . . . modes, including those used by and/or by Dr David Maddison available to radio amateurs. vi) Amateur radio digital modes 1) FreeDV for radio amateurs FreeDV (https://freedv.org/) is an amateur digital mode for HF (shortwave frequencies). It uses either a computer and soundcard for encoding/decoding or a dedicated device, and is shown in Fig.17. Many other digital modes, even though they have open-source software, use proprietary codecs. But FreeDV uses an open-source codec. It uses neural net speech coding called LPCNet (www.rowetel.com/?p=6639) Fig.17 (right): a screengrab of FreeDV in operation. Image courtesy Mark, VK5QI 12 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.18: an image received via FSQ. and is called Codec 2 (www.rowetel. com/?page_id=452). This enables a very low data rate transmission of voice, eg, using just 1.1kHz bandwidth. The modern implementation of Codec 2 was developed by Australian Ham Dr David Rowe VK5DGR and others. See the video titled “David Rowe interviewed about Codec2” at https://youtu.be/ Nzf4XCCwHoI 2) FSQ Fast Simple QSO (where QSO means contact in the radio Q Code) is a relatively new digital mode for amateur radio, released in 2015. It is like a chat program with each side typing messages to which the other responds, and it also supports the transfer of images (see Fig.18). It can be used on HF (shortwave) and has been adapted for VHF, using FM in both cases. Each party can transmit to the other at a different speed. There are agreed-on, dedicated frequencies for its use. FSQ uses an efficient alphabet coding whereby most common characters can be sent with just one symbol, or at most, two for less common characters – see Fig.19. A symbol is a pulse or tone in digital transmission systems, representing an item of information. It could be 0 or 1 in the simplest schemes (ie, binary coding), but more advanced siliconchip.com.au schemes use many more states. The typing rate can be as high as 60 words per minute (wpm) using 290Hz Symbol(s) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Char SPACE a b c d e f g h i j k l m n o p q r s t u v w x y z . CRLF Symbol(s) 0–29 1–29 2–29 3–29 4–29 5–29 6–29 7–29 8–29 9–29 10–29 11–29 12–29 13–29 14–29 15–29 16–29 17–29 18–29 19–29 20–29 21–29 22–29 23–29 24–29 25–29 26–29 27–29 28–29 Char <at> A B C D E F G H I J K L M N O P Q R S T U V W X Y Z , ? of bandwidth at 5.86 baud. This is the same typing rate as RTTY with only about 1/8th the baud rate, since RTTY uses just one bit per symbol, so a character needs 7.5 symbols, plus it uses additional data for synchronisation. Additional advantages of FSQ are: • no synchronisation is required between the two stations, making it more resistant to propagation delays, noise and avoiding time wasted synchronising • each party can transmit at their own speed of 2, 3, 4.5 or 6 baud, corresponding to around 20-60wpm; 4.5 baud being the most common rate used • messages can be sent to one station or a number at the same time. Pictures can be transmitted using an analog format with similar bandwidth, using Near Vertical Incidence Skywave (NVIS) for less noise (a technique where the radio transmission is bounced off the ionosphere with a near-vertical angle for transmission ranges up to 650km). A 320 x 240 pixel colour image would take just over three minutes. FSQ uses incremental frequencyshift keying (IFK+), a type of frequencyshift keying (FSK) which confers Symbol(s) 0–30 1–30 2–30 3–30 4–30 5–30 6–30 7–30 8–30 9–30 10–30 11–30 12–30 13–30 14–30 15–30 16–30 17–30 18–30 19–30 20–30 21–30 22–30 23–30 24–30 25–30 26–30 27–30 28–30 Char ~ 1 2 3 4 5 6 7 8 9 0 ! quote # $ % & ( ) * + − / : ; < > IDLE Symbol(s) 0–31 1–31 2–31 3–31 4–31 5–31 6–31 7–31 8–31 9–31 10–31 11–31 12–31 13–31 14–31 15–31 16–31 17–31 18–31 19–31 20–31 21–31 22–31 23–31 24–31 25–31 26–31 27–31 28–31 Char = [ \ ] ^ { } ` ± ÷ ° × £ BS DEL Fig.19: the FSQ symbol table. It is a type of “varicode”, where more common letters use one symbol and the less common ones use two. Australia’s electronics magazine May 2021  13 Fig.20 (left): a representation of FSK modulation showing an unmodulated carrier wave in the centre, the data to be transmitted at top and how that data is modulated onto the carrier wave at the bottom. Source: Wikimedia user Ktims. Fig.21 (above): phase-shift keying (PSK), where the change in carrier signal phase encodes data. resistance to multipath propagation errors and frequency drift. IFK was invented by an Australian, Steve Olney (VK2XV/VK2ZTO) and is implemented in several other digital modes such as JASON, DominoEX, Thor and Throb. For more details of that transmission scheme, see siliconchip.com.au/ link/ab6m 3) ASK (amplitude shift keying) represents data by variations in the carrier wave’s amplitude. OPERA is an example of a beacon system that operates with this modulation. 4) FSK (frequency-shift keying) is a modulation scheme whereby information is transmitted via frequency changes in the radio carrier wave (see Fig.20). FSKH105 is an example, while MSK144 is a variation of FSK designed for communication via meteor scatter. FST4 and FST4W are new digital modes that use Gaussian FSK. 5) MFSK (multiple frequency shift keying) and GFSK (Gaussian FSK) are variations of FSK. MFSK8 and MFSK16 are radio ham variations of FSK, designed explicitly for keyboard conversations via HF long-path DX (distant reception), and were the first amateur digital modes, introduced in 1999. Other MFSK modes are Olivia, Contestia, JT65, FSK441, JT6M, WSPR, FT4, JS8, FT8, FSQ, THROB, WSQ, WSQ2, Q65. MEPT_JT is a mode intended for propagation testing, not keyboard conversations. 6) IFK and IFK+ (incremental FSK) are variants of MFSK. DominoEX and 14 Silicon Chip Thor use this modulation scheme. EXChat is a variation of DominoEX. 7) PSK (phase-shift keying) is a modulation scheme in which the phase of a carrier wave is changed to convey information – see Fig.21. Examples include PSK31, PSK63, MT63, 2-PSK, 4-PSK and Q15X25. 8) ROS is an amateur radioteletype mode. According to www.sigidwiki. com/wiki/ROS it uses a “combination of FHSS (Frequency Hopping Spread Spectrum), DSSS (Direct Sequence Spread Spectrum) and 2G (Second Generation) CDMA (Code Division Multiple Access)”. RSID (Reed-Solomon identification) is a method to identify digital modes; see www.w1hkj.com/RSID_ description.html There is a demonstration of the JS8 mode by prominent Australian radio amateur in the video “JS8: My first contact” at https://youtu.be/ZAfb3x3b8xc vii) Non-amateur digital modes and shortwave applications 1) SailMail (https://sailmail.com/) is a non-profit association of yacht owners to enable them to send emails beyond line-of-sight. According to the website, email can be transferred via any form of internet access such as “Iridium, Inmarsat, VSAT, Globalstar, Thuraya, terrestrial WiFi, terrestrial cellular networks, or via SailMail’s own worldwide network of SSB-Pactor radio stations”. It is based on the Winlink software described later. Australia’s electronics magazine 2) PACTOR is a radio modulation mode used by amateurs, commercial, government and military operators alike. It is based on AMTOR and packet radio. AMTOR (amateur teleprinting over radio) is known commercially as SITOR (simplex teleprinting over radio). 3) CLOVER refers to a series of commercial radio modem modulation techniques used in HAL Communications Corp products. viii) Weak-signal modes WSJT (https://physics.princeton. edu/pulsar/k1jt/) and related programs are open-source software designed for weak-signal digital modes. WSJT supports the weak-signal modes of JTMS, FSK441, FSK315, ISCAT, JT6M, JT65, and JT4. WSJT-X (Fig.22) supports FT4, FT8, JT4, JT9, JT65, QRA64, ISCAT, MSK144, and WSPR, as well as one called Echo, designed for receiving your own signal via moon bounce propagation. See also the related section below on beacons and WSPRnet. ix) Beacons and reverse beacons Beacons and reverse beacons help radio operators, including hams, to assess radio propagation conditions on particular bands and between specific locations. Propagation conditions change because of changes in the ionosphere about 48km to 635km above the Earth, from which radio waves are reflected or refracted. These changes are due to time of day, season, weather and sunspot activity. siliconchip.com.au Fig.22: a screengrab of WSJT-X. Source: Amateur Radio Experimenters Group (AREG) in Adelaide (www.areg.org. au/wsjt-x). 1) The amateur NCDXF/IARU International Beacon Project (www.ncdxf. org/beacon/index.html) is a conventional beacon network – NCDXF is Northern California DX Foundation, and IARU is the International Amateur Radio Union. The beacon locations worldwide are shown in Fig.23, including VK6RBP in Perth (www. vk6uu.id.au/vk6rbp.html). Signals are sent out at various set times, frequencies and power levels and individual stations monitor them to determine propagation conditions between the beacon and themselves. In the aforementioned network, signals are sent out every three minutes at reducing power levels of 100W, then 10W, 1W and 0.1W and at different frequencies. You can listen to these beacons without a radio using the online receivers at http://ve3sun. com/KiwiSDR/ In a reverse beacon network such as WSPRnet, PSK Reporter or Reverse Beacon Network (RBN) (see below) a user listens for transmissions, just as in a conventional beacon network. But instead of the transaction finishing with a user just hearing the beacon, the RBN user then reports via the call sign, signal strength and other information back to a central database via the internet. Therefore, ‘openings’ on propagation conditions can be spotted. 2) WSPRnet (Weak Signal Propagation Reporter Network; http://wsprnet. org/drupal/), shown in Fig.24, is an RBN that only hears transmissions intended for WSPRnet ‘spotting’. It uses an extremely sensitive low-power digital mode called MEPT_JT (Manned Experimental Propagation Transmitter; JT are the inventor’s initials) to test propagation conditions and report to a database. The MEPT_JT protocol was developed in 2008 with the objective of creating a tool for ionospheric sounding that used very little power and bandwidth (6Hz), but with very high sensitivity. Each sounding station can send or receive signals, or both. It is used on LF, MF and HF frequency bands. MEPT_JT messages are tightlycoded to have as much information as possible, and contain forward error-correction and the signal. Current software can detect this at a -27dB signal-to-noise ratio in 2.4kHz of bandwidth. Like some other digital radio modes, such weak signals can be detected because of their extremely low bandwidth, with known timing of the data bits and error correction. Each message is 50 bits long and takes about two minutes to transmit. In addition to the message bits, there is a 162-bit pseudorandom noise sequence transmitted for synchronisation. The symbol rate is 1.466 baud (ie, the number of changed signal states per second) with two bits per symbol transmitted. It uses IFK modulation. For technical details of how the MEPT_JT mode works, see siliconchip. com.au/link/ab6o You don’t have to be a radio ham to become a WSPR listener and reporter, but you do have to be one to transmit signals. 3) PSK Reporter (https://pskreporter.info/) is a service whereby radio amateurs run client software and monitor the bands for amateur radio digital voice modes. The results are automatically relayed to a central server (see Fig.25). Nothing is transmitted; the system just listens and logs CQ calls (requests for a conversation) and a previously Fig.23: the beacon locations for the International Beacon Project siliconchip.com.au Australia’s electronics magazine May 2021  15 Fig.24: WSPRnet propagation reports plotted according to frequency band over a 24-hour period. Current maps can be viewed at http://wsprnet.org/drupal/wsprnet/map or see http://wsprd.vk7jj.com/ registered participant call sign (with location) via digital modes. As no transmission is involved, you can participate in PSK Reporter without being a radio ham. Watch the video titled “PSK Reporter: How You Can Be Part! AD #33” at https://youtu.be/ HwlpnQb6E6k One difference between WSPRnet and PSK Reporter is that WSPRnet runs fully automatically, and you can check who heard you and whom you heard whenever you want; it requires no interaction from the user. With PSK Reporter, you monitor existing conversations (QSOs) between stations and have to tune them in and respond etc. The signals are not deliberately sent to obtain propagation reports as with WSPRnet. The amateur radio Reverse Beacon Network (www.reversebeacon.net) is a system of volunteers who monitor the amateur bands with broadband software-defined radios (SDRs) and report back to a sender via the internet where in the world they have heard that sender’s signal. They run software listening for CQs or TEST messages followed by a callsign on Morse, RTTY or PSK31. In contrast to PSK Reporter and WSPRnet, this system, when used with CW Skimmer software (Fig.27; www.dxatlas.com/ cwskimmer/) and SDRs can be used to report activity across multiple frequen- Fig.25: a map from PSK Reporter showing propagation conditions on various bands. 16 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.26: the WIRES-X scheme. C4FM is a proprietary Yaesu digital mode for amateur radio to transmit voice and data implemented on certain radio models (siliconchip.com.au/link/ab6w). cies and bands simultaneously, due to the wide bandwidth of SDRs. For more information, see the video titled “The Ham Radio Reverse Beacon Network, AD#32” at https://youtu. be/4Y5ZHqfeJgo x) Radio over the Internet Apart from the fact that most commercial radio stations stream live over the internet, various amateur radio projects involve linking some part of a radio transmission via the internet. 1) WIRES-X (Wide-coverage internet repeater enhancement system) is a Yaesu-developed standard (siliconchip.com.au/link/ab6p) to enable equipped radios to connect to internet gateways and establish connections with other users – see Fig.26. The radio’s connection to the gateway is made via a digital voice and data modulation mode called C4FM, which is backward-compatible with analog FM. Australia has several C4FM compatible repeaters; see http:// siliconchip.com.au/link/ab6q 2) The Free Radio Network (www. freeradionetwork.eu) enables radios to connect to an internet gateway, transmit via voice over IP (VoIP), then reconnect to another gateway and another radio somewhere else. 3) EchoLink (www.echolink.org) is a free system for radio amateurs that enables them to communicate with other hams throughout the world, by routing part of the connection over the internet using VoIP – see Figs.28 & 29. A connection can be made as long as the initiating radio and the receiving radio are in wireless range of an EchoLink node. The software is available for all popular platforms and smartphones. 4) IRLP (The Internet Relay Linking Project; www.irlp.net) routes amateur calls from radio to the internet, then back to radio again at any location worldwide where there is an IRLP gateway (a “node”). The node contains both a transceiver and a computer with an internet connection. Radio amateurs within range of the node contact the node and enter DTMF tones to indicate the remote node they Fig.27: a screengrab of CW Skimmer (www.dxatlas.com/cwskimmer/). This software listens for CW (Morse code) signals, extracts the call signs, logs and transmits them if necessary, for monitoring applications such as the Reverse Beacon Network. Fig.28: how EchoLink works. siliconchip.com.au Australia’s electronics magazine May 2021  17 siliconchip.com.au/link/ab6t xi) Internet over radio Fig.29: the EchoLink software. want to connect to. Voice is carried by a VoIP protocol. There are 49 IRLP nodes in Australia and thousands worldwide. 5) DMR (Digital Mobile Radio) is an international standard for commercial, personal and amateur communications, ratified in 2005. A list of Australian DMR repeaters is at siliconchip.com. au/link/ab6r 6) D-Star (https://3fs.net.au/dmr-inaustralia/) is the first digital radio system designed specifically for amateur radio (see Fig.30). It was developed in the late 1990s by the Japan Amateur Radio League. It can be used for voice and data and over the air or via internetconnected gateways. It is suitable for HF, VHF, UHF and microwave amateur bands. There is a list of Australian D-Star repeaters at siliconchip.com.au/link/ab6s 7) QsoNet virtual ionosphere (www. qsonet.com) is amateur radio without the radio. The system simulates the ionosphere, and licensed amateurs speak to each other via the internet with VoIP. The modes allowed are voice, CW (Morse code), PSK and FSK on five bands. It is a paid service with a 30-day free trial then US$39 per year. See Fig.31 and the video titled “CQ100 VOIP Ham Radio Transceiver” at https://youtu.be/ YagTAAI4Yq4 There are many aids to assist visually impaired or disabled people with conventional radio equipment. QsoNet can also help such people because they don’t have to get on roofs to install or maintain antennas etc. It is also used by people who have living circumstances that prohibit them from installing appropriate antennas, 18 Silicon Chip or where radio propagation conditions are poor. 8) HamSphere (http://hamsphere. com/) is a subscription service for radio amateurs and others to use a smartphone or PC to simulate radio ham communications over the internet, complete with simulated propagation conditions. See the video titled “HamSphere – How it looks and sounds in action” at https:// youtu.be/zJNWSmsXjEU 9) Remote amateur transceiver control. Due to a radio-poor location or the inability to set up satisfactory antennas, such as for apartment-dwellers, many radio amateurs are choosing to operate their transceivers remotely over the internet. For an Australian example, see The internet can be accessed over HF radio links, but generally at a relatively low speed. 1) Automatic Link Establishment (ALE) is a protocol for establishing digital links on HF. ALE establishes a connection for voice and data exchange. ALE uses automatic channel selection, scanning receivers, selective calling, handshaking, and robust modems to find the best available operating frequencies for a link. If internet connectivity is required, High-Frequency Internet Protocol (HFIP) can be employed. STANAG 5066 is an example of an HFIP standard. There is an amateur radio HFIP network called HFLINK (see http:// hflink.com). 2) Barrett Communications (siliconchip.com.au/link/ab6u) is an Australian company that offers a commercial email and data transfer over HF system, the 2020 HF Email fax and data system. 3) AMPRNet of The Amateur Packet Radio Network is used to transfer data between computer networks. A part of AMPRNet is the Europeanbased High-speed Amateur-radio Multimedia NETwork (HAMNET; https:// hamnet.eu/), covering 4000 nodes in central Europe. 4) HamWAN (http://hamwan.org/) is a multi-megabit, IP-based digital network for amateur radio use in the Fig.30: D-Star connectivity. Source: Dave VK3LDR. Australia’s electronics magazine siliconchip.com.au Silicon Chip Binders REAL VALUE AT $19.50 * PLUS P &P Fig.31: a virtual “CQ100” transceiver of QsoNet. United States. It is in western Washington state and expanding. 5) Winlink (www.winlink.org) is a volunteer-administered system to send emails worldwide via licensed radio amateurs – see Fig.32. It can operate on amateur HF and other bands, or if the internet is not available, through a mesh called Winlink Hybrid Network. See the two videos titled “What Is Winlink?” at https://youtu.be/ qGhUfW8pjY8 and “Email using Ham Radio! It’s FREE!” at https://youtu. be/1Gf1fJFfTok xii) Digital radio messages for ships and aircraft 1) NAVTEX or Navigational Telex is a digital radio mode for automated receive-only navigational messages and alerts for maritime operations. It is free and transmitted on 518KHz for international English service, and 490kHz in local languages (just below the AM broadcast band). There is also a Marine Safety Information broadcast on HF 4209.5kHz. It has a design range of 200 nautical miles (about 370km). If you are interested in receiving NAVTEX yourself with an SDR, see the video titled “Decoding NavTex with Software Defined Radio – SDRuno RSPdx” at https:// youtu.be/9b6w5Me6tpU 2) ACARS (Aircraft Communications Addressing and Reporting System) and AIS (Automatic Identification System) are for identifying and tracking aircraft and ships, using signals that are continuously transmitted. You can monitor these fairly easily with various decoding programs and with a regular receiver that can receive 129-137MHz, or an SDR. We published detailed articles on AIS and how to receive AIS transmissions in the August 2009 (siliconchip.com. au/Article/1528) and January 2010 (siliconchip.com.au/Article/41) issues. xiii) PICO balloons We first looked at PICO balloons in Are your copies of SILICON CHIP getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of SILICON CHIP. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H SILICON CHIP logo printed in gold-coloured lettering on spine & cover Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Fig.32: a screenshot of Winlink. Source: Denver Amateur Radio Emergency Service. siliconchip.com.au Australia’s electronics magazine Order online from www.siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *See website for delivery prices. May 2021  19 Fig.33: this small balloon circumnavigated the world six times. Source: www.qrp-labs.com/images/circumnavigators/hirf6.jpg our February 2015 issue (siliconchip. com.au/Series/281), describing the work of Australian Andy Nguyen VK3YT. PICO balloons are Mylar party balloons like you would get from a party supply shop. Balloonists attach a tiny transmitter package to them weighing as little as 10.5 grams. Their location is tracked by GPS, and sensors measure temperature and pressure. This data is transmitted to and recorded by ground stations – see Fig.33. Power comes from batteries or supercapacitors which can be recharged by tiny solar panels. The transmissions are on VHF or UHF with a range of approximately 380km, or HF with a range of up to 16000km at just 25mW. How is such an incredible range achieved with such a tiny amount of power? PICO Balloons may use APRS (Automatic Packet Reporting System) with amateur radio digital modes such as Olivia or THOR on VHF or UHF, or on HF they may use JT9, JT65 or WSPR (Fig.34). The signals are received and uploaded to a tracking site, or propagation reports are sent to WSPRnet. For information on Australian PICO balloon releases, see siliconchip.com. au/link/ab6v and http://picospace.net/ You can track a variety of balloons worldwide at https://tracker.habhub. org/ equivalent to the time light or radio waves take to travel ~3000km. Signals might not just be delayed; they can suddenly appear to become advanced as a shorter signal path is established, so observing a static data bit being repetitively sent, it would seem to move back and forth with respect to any particular time reference. Any digital mode relying on ionospheric propagation, either through it such as with GPS satellites and other digital modes from satellites, or via reflection such as from one location on Earth to another, must be able to take account of and compensate for these significant timing differences. Even at the very slow speed of radioteletypes, which operated at 45bps, each bit took 22ms to transmit. So a delay of 10ms could introduce significant errors into the received data bits. With faster modern modes, the problem is far worse. These effects are apparent with the Hellschreiber, as shown by the distortion of the text, or can be heard if you listen to a shortwave radio station. xv) Mesh networks Mesh networks are a type of computer network architecture that is nonhierarchical, self-configuring and selforganising. The functions of routers, switches, bridges etc are performed within each device, or node, within the mesh (see Fig.35). As conditions change, such as a node being removed from the network, the mesh network can dynamically reconfigure itself using adaptive or dynamic routing technology to automatically choose the shortest and best route to send and receive data. It is said to be ‘self-healing’. Mesh networks have applications where a large number of similar devices need to be part of a network. Examples include: • smart electricity or other utility meters xiv) Ionospheric problems HF signals reflected from the ionosphere can have propagation delays and multiple paths due to changing conditions. Signal delays can be as much as 10ms and the signal can be Doppler shifted in frequency. 10ms is 20 Silicon Chip Fig.34: a commercially-available WSPR transmitter for a PICO balloon from ZachTek (www.zachtek.com/product-page/wspr-tx-pico-transmitter). It weighs 10.5g without an HF antenna and balloon harness, and can have an output power of 20mW on the 20m and 30m amateur bands. It is Arduino-based and uses open-source software. Some PICO balloon operators make their own. Australia’s electronics magazine siliconchip.com.au Fig.35: the architecture of a wireless mesh network with multiple types of devices connecting into it. Source: J. Rejina Parvin DOI: 10.5772/intechopen.83414. • environmental sensor networks • battlefield surveillance and soldierto-soldier communications (the technology was originally developed for the military) • tunnel surveillance • security surveillance cameras • mobile video such as sports/racing cameras • emergency services communications • home and commercial building monitoring and automation (eg, with ZigBee) • industrial monitoring and control • medical monitoring • connection of consumer electronic audiovisual equipment • automotive • broadband wireless connections within homes or commercial buildings • environmental monitoring • Iridium satellites • security systems The modulation schemes used in wireless mesh networks are the same as WiFi and governed by standards such as IEEE 802.11a through to 802.11ax, 802.11s and 802.21. xvi) LoRa and LoRaWAN LoRa and LoRaWAN (Long Range Wide Area Network) are fascinating relatively new digital radio transmission technologies offering the advantages of low cost, low power consumption and long range (see Fig.36 & Table1). They use a technology called Chirp Spread Spectrum in which a ‘chirp’ signal is transmitted over a broad bandwidth, making it resistant to noise and fading. siliconchip.com.au Fig.36: typical throughputs and ranges for some common digital wireless technologies. Higher throughput means a greater data bit rate, but also requires high powers to get good coverage. Greater ranges can be obtained with low power but also at a lower bit rate. Source: DOI: 10.1088/1755-1315/195/1/012066. A chirp signal is an FM sinewave signal that increases or decreases in frequency over time, often with a particular mathematical pattern (see Fig.37). There is always a trade-off in radio, so even though LoRa is long-range and lowpower, it also has a relatively low bit rate, so cannot be used for voice or video. LoRa is one of the core technologies of the Internet of Things (IoT) – see www.thethingsnetwork.org and SILICON CHIP, November 2016 (siliconchip. com.au/Article/10425). LoRa transmits on license-free radio bands. In Australia and North America, it uses 915MHz; in Europe, 868MHz; and in New Zealand, both. LoRaWAN is a form of LPWAN (Low-Power WideArea Network). LoRa’s features include: • standardised protocol • up to 50km range under ideal conditions • low-power operation • encryption • geolocation data available due to built-in GPS • low-cost • base stations have a high capacity for messages from connected devices It has numerous applications, such as: • monitoring agricultural or environmental sensors • • • • smart buildings and cities utility metering emergency service industrial control Its low cost enables the roll-out of devices in huge numbers. LoRa can achieve a data rate of up to 50kbps with channel aggregation, but for something like a sensor, it might just need to send a few bytes, such as its location and temperature. The modulation technique used is proprietary to the LoRa Alliance (https://lora-alliance.org/) and not open-source. LoRa devices can also be tracked without GPS using differential time-of-arrival (DTA) techniques. The current world record distance for LoRaWAN communication is 702km, but it is usually 2-3km in urban areas and 5-7km in rural areas. LoRa can also be used as part of a mesh network. See the video titled “#337 LoRa Mesh Communication without Infrastructure: The Meshtastic Project (ESP32, BLE, GPS)” at https:// youtu.be/TY6m6fS8bxU xvii) Off-grid communications Several communications systems are being developed based on fully self-contained mesh networks, and require no existing infrastructure. 802.11n (WiFi) 4G mobile LoRaWAN Throughput <300Mb/s 100Mb/s+ <1Mb/s Range 100-200m 2-10km 20km+ Battery life Days Days Years Table1: typical performance of WiFi, 4G and LoRaWAN devices. Australia’s electronics magazine May 2021  21 Fig.37: the frequency variation of a LoRa signal with time. Fc is the centre frequency and BW is the bandwidth. Source: DOI: 10.3390/s16091466. These include: 1) Locha Mesh (https://locha.io/), to transfer Bitcoin and Monero cryptocurrencies and chat without the internet. 2) Project OWL (www.project-owl. com), to establish off-grid networks with open-source software for a variety of purposes such as natural disasters, government for C4ISR (Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance), mass networking at major public events such as sport, and industry to support large scale sensor networks. Project OWL uses the ClusterDuck Protocol (http://clusterduckprotocol. org/), which is open-source firmware for mesh network IoT devices based on LoRa radio. 3) Lantern Works (www.lantern. works) is another mesh-based disaster recovery network. 4) Disaster.radio (https://disaster. radio/), as the name implies, is an offgrid, self-contained communications network to provide communications during natural disasters when all other infrastructure may have failed – see the video titled “What is disaster.radio?” at https://youtu.be/uZkGudvjNzw It uses many low-cost, solar-powered nodes to create a mesh network. Each of these nodes acts as a WiFi access point that can be communicated with via smartphones. The smartphones do not need to be connected to any network, but they do need the disaster.radio App installed before the disaster. The network is based on free, open-source software and inexpensive open-source hardware. 5) The PT01 Power Talkie (www. ptalkie.com) is a walkie-talkie type device that lets you use your smartphone to send messages when no mobile connection exists. It operates by creating a mesh network with other uses. It operates at UHF frequencies of 462MHz (USA) and has a range of about 1.5km in urban areas and 5km in the country. See the video titled “PowerTalkie Mesh Network – Maintain Smartphone Communication Off Grid!” at https:// youtu.be/aPKKmzRbSp0 6) Meshtastic (www.meshtastic.org) is an open-source community project. The devices establish a mesh network to communicate. xviii) Off-grid Internet Othernet (https://othernet.is/) is a company that sells an inexpensive satellite receiver (shown in Fig.38). It can receive free broadcasts from its satellite of various internet-based digital content such as news, information, education materials, radio programs, emergency information, weather data, the entire contents of Wikipedia and any type of data file. It is also possible to make one yourself with an SDR. The data is broadcast only from its satellite, with no consumer uplink, so all the information on offer is contin- Fig.38: an Othernet satellite “Dreamcatcher 3.05” transceiver with a range of 85-6000MHz. It is suitable for various forms of communication apart from satellite reception of Othernet broadcasts. It is now obsolete and will be replaced with a device that can only receive on 2400MHz. If you are interested in Othernet, check there is satellite reception in your area. uously transmitted and downloaded into a data cache. Other devices can be connected to the receiving device by WiFi to access the information. See the video titled “Othernet Dreamcatcher: Free Internet content” at https://youtu. be/0F57ARpZFig xix) Other digital radio technologies 1) Digital mobile phones The latest digital mobile telephony technology was discussed in the article on 5G, in the September 2020 issue (siliconchip.com.au/Article/14572). 2) Timekeeping signals Digital radio signals are also broadcast in many countries for timekeeping services. See my article on that topic in the February 2020 issue (siliconchip. com.au/Article/14736). 3) Satellite navigation We discussed digital radio signals for satellite navigation in detail in the October 2020 (siliconchip.com. au/Article/14597), November 2019 (siliconchip.com.au/Article/12083) and September 2018 (siliconchip.com. au/Article/11222) issues. SC Online SDRs If you don’t have any receiving equipment, you can still listen to various online SDR radios. This one is in Melbourne at http:// sdr-amradioantennas.com:8073/ and there is a worldwide list of online SDRs at www.websdr.org Even if you do have receiving equipment, you won’t necessarily be able to hear distant signals, but you can connect to an SDR closer to your area of interest. 22 Silicon Chip Here is one in Araluen, NSW: http://tecsunkiwisdr.access. ly:8073/ There is also a list of a certain brand of online SDR hardware called KiwiSDR at http://kiwisdr.com/public/ KiwiSDR is a type of commercially-made receiver that you can place online to run a streaming SDR feed by connecting it to a tiny BeagleBone Black open hardware Linux PC (see https://beagleboard.org/black). Australia’s electronics magazine siliconchip.com.au