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Digital Radio Modes You are probably familiar with digital radio and broadcast technologies like DAB+, DRM, DVB-T and LoRa (we have reported on all of these in the past). But digital radio is a lot more widespread than most people would realise. It’s used extensively by amateur radio operators, industry, governments, militaries and many others and there are dozens of different modes. Read on and learn more; much more... more... 14 Silicon Chip Australia’s electronics magazine Part One . . . by Dr David Maddison siliconchip.com.au M any analog radio communication modes are being phased out in favour of digital methods. Some relatively recent examples include the switch to digital TV (DVB-T) and the introduction of digital broadcast radio (DAB+) and digital radio modes for commercial, government and radio amateur use. Advantages of digital radio modes include: • greater voice clarity • interference immunity • proper encryption • more efficient use of the radio spectrum • greater channel capacity • faster channel changing or searching • the ability to add new functions to radios as new software and applications are developed Disadvantages of digital radio include: • more complicated software • possibly higher costs compared to analog (especially with proprietary systems) • intolerance of major RF interference (despite good tolerance to minor interference) • the ‘digital cliff’ at extreme range, where communication suddenly drops out compared to analog, which gradually fades out Analog radio still has some benefits such as relatively simple and well-understood equipment and hardware-only solutions with no software to go wrong. Remaining analog radio in common use, for the moment, includes: • AM and FM broadcast radio (although some other countries have already phased these out) • HF and UHF CB (citizens’ band) • standard amateur radio modes • commercial and government shortwave services • various short-range transmitters such as baby monitors and wireless doorbells (which can be either digital or analog) Of all the analog radio modes, it is most likely that broadcast AM and certain government-sponsored shortwave services will last the longest before being phased out, as the ownership of these types of analog receivers is vast worldwide. Digital radio history Overall, though, the advantages of digital radio greatly outweigh analog radio. On 27th July 1896, Guglielmo Marconi first publicly demonstrated ‘wireless’ signals, and in March 1897, he transmitted Morse Code signals over 6km. That was interesting because Morse Code is arguably a form of digital radio transmission, so the concept of digital radio isn’t altogether new. Early digital radio modes such as RTTY (radioteletype) were successfully tested as early as 1922, and have been in commercial use since 1932. However, the data throughput at the time was relatively low, typically 60 words per minute (wpm) for RTTY45 mode at 45.45 baud (bits per second) to 100 wpm in RTTY75 mode at 75 baud. Much higher data rates have become possible because of large increases in computing power and digital signal processing technology. Computers can also compress data, conserving radio bandwidth. There are vast numbers of digital radio modes, and we can’t cover all of them in this article. So we will describe the most interesting or unusual techniques. Digital radio basics With digital radio (or TV), information is transmitted via radio waves in discrete steps, rather than with the continuous gradation of values used for analog transmissions. The advantage is that the original data can be precisely reproduced at the receiving end with close-to-ideal reception. In contrast, an analog signal is always subject to some degradation of the original signal (eg, noise). Just like analog radio, which uses a variety of modulation schemes such as SSB (single sideband), AM (amplitude modulation), FM (frequency modulation) etc, various digital modulation schemes can be used. There’s also the option of digital compression, which is applied to the data before it is transmitted and reversed upon reception. This reduces the amount of data that needs to be transmitted. i) Early Digital Modes 1) Morse code Arguably, the first digital mode was Morse code (also known as CW), first used in 1844. Information is sent as a short “dot” (normally refrred to as a dit), or longer “dash” (known as a dah), with spaces being delineated by a lack of transmission. The “dah” is nominally three times the duration of the “dit”. There is a one-dit-length gap between each dit or dah within a group, a three-dit-length gap between ‘letters’, and a seven-dit-length gap between each word. What is not commonly realised today is that the “American” code Morse developed (originally for the US telegraph service), and the “Continental” or “International” Code we know today, bear only a passing resemblance to each other. Some letters are the same but the American code also has long daaaaahhhhs and spaces within letters. It has all but died out these days; even the Gugliemlmo Marconi (1874-1937), acclaimed as “the father of radio”. He is shown at left with his apparatus assumed to be set up on the Isle of Wight around 1897/8. At right is the illustration from his radio patent. siliconchip.com.au Australia’s electronics magazine April 2021  15 theory which was not established until 1948 (it is similar to Huffman coding). For reference, “SILICON CHIP” sounded in Morse code looks like this: dididit didit didahdidit didit dahdidahdit dahdahdah dahdit dahdidahdit didididit didit didahdahdit Samuel FB Morse (1791-1872), generally credited with the code which bears his name and, perhaps more importantly, the telegraph system which used it. More detail: en.wikipedia.org/wiki/Samuel_Morse International Code has few users (mainly amateur radio operators dedicated to keeping it alive!). Morse code was created with maximum efficiency in mind. The more common letters were coded with the shortest sequences, and less common letters with longer sequences. The most common letter “E” is simply “dit” and a “T” is “dah”. Conversely, a “Q” is “dah dah didah” It turns out that Morse code is close to the optimal efficiency for encoding data, as is predicted by information (Only when there is a space following a “dit” is the “t” at the end sounded; otherwise it is shortened to “di”– the dits and dahs flow into each other). Note too that Morse code is an aural, as distinct from a visual, language – hence the dits and dahs. You will often see it written down as dots and dashes (eg, A = .–) but this is discouraged, especially if you are trying to learn the code. You can write your own code sequences and see how they look and sound at the following website: siliconchip.com.au/link/ab65 2) Radioteletype Teleprinters are electromechanical printers that can print information transmitted either over a wire (telegraphy), leased line, telephone circuit, or radio waves, as in a radioteletype or RTTY. The Teletype Corporation Model 15 was an extremely popular machine that was in production from 1930 un- Fig.1: a Model 19 radioteletype. These machines are still used today by radio amateurs and computer enthusiasts for fun. Source: www.railroad-signaling.com 16 Silicon Chip til 1963. The Model 19 (Fig.1) was a Model 15 with a paper tape unit and a Model 14 transmitter distributor. The model 14 reads the paper tape encoded with a 5-bit Baudot-Murray US TTY version of ITA2 code and transmits it via landline, or it can key a radio transmitter for wireless transmission. The US Navy commonly used the AN/FGC-1 diversity FSK converter and its companion AN/FRR-3 diversity receiver to receive RTTY comms (see www.navy-radio.com/rcvr-div. htm). Radio amateurs appear to have started using surplus RTTY units in the 1940s around the New York area. For more information, see the following videos: • “Teletype Model 19 (and Model 15) Demonstration” – https://youtu.be/ jxkygWI-Wfs • A 19 part series “Teletype Model 19 - Part 1: A Teletype Arrives for Restoration” – https://youtu.be/ _NuvwndwYSY • “Using a 1930 Teletype as a Linux Terminal” – https://youtu.be/ 2XLZ4Z8LpEE 3) Hellschreiber The German Hellschrieber (Schrieber means printer), invented by Rudolf Hell, was a surprisingly advanced instrument, implementing a form of Fig.2: a Hellschreiber machine. Characters are encoded on a spinning drum behind the keyboard and decoded messages (or sent messages), are printed out on a strip of paper on the right. Australia’s electronics magazine siliconchip.com.au Fig.4: a printed message from a Hellschreiber with slight timing errors. The message is still intelligible because it is printed twice. Source: Wikimedia user Mysid. Fig.3: how a Hellschreiber creates the letter E, and the corresponding transmitter carrier. Note that the letters written on the wheel are column designators. Source: video by J. Mitch Hopper titled “Hellschreiber - What is that?” at https://youtu.be/Ayhf51fUpLs what we now know of as dot-matrix printing (Fig.2). This was equivalent to a teleprinter but was mechanically much simpler and cheaper. It was invented in 1925, and in 1929, Hell patented the invention and founded a company to produce it. It was first used in the 1930s for press services, and was later used during World War 2. Like a teleprinter, it could be connected to another device either by a wired connection, such as a landline, or via a radio link. However, the inventor stated that “The development of the Hellschrieber was specifically done for wireless communication” and he also said, “The objective of the development was a practical device for the reception of messages from news agencies. This could only be achieved with a very simple teleprinter.” It was still in use well into the 1980s. It has developed into a software-based radio amateur standard using a sound card on a PC and an external transceiver, because original machines are rare and hard to find. A fundamental difference between the Hellschreiber and a teleprinter is that a teleprinter or teletype transmits data via coded symbols such as the 5-bit Baudot code. Teleprinters have no data siliconchip.com.au Fig.5: a modern emulation of Hellschreiber using software from radio amateur Nino Porcino IZ8BLY (http://antoninoporcino.xoom.it/Hell/index.htm). Source: Ernie Mills, WM2U. redundancy, so in the event of interference, data can be lost or the wrong character printed, or start (synchronisation) bits missed or misinterpreted. But with the Hellschreiber, characters are not sent encoded. Characters are represented by a 7x7 matrix (larger matrices are possible) and they are sent as a raster image – see Fig.3. There might be image distortion in the event of a noisy transmission, as shown in Fig.4, but no incorrect characters, since there is no encoding to be corrupted. There are no start bits sent to synchronise with the receiving machine, so nothing to miss or misinterpret. The device requires a small signal bandwidth and can be used over conventional voice channels, even when they are too degraded for useful voice transmission. It can even be used with equipment designed for CW (Morse) telegraphy. Several different wireless transmission modes can be used, such as PSK (phase-shift keying), FM (frequency modulation) and multitone. When a particular letter is pressed, say “E” as in Fig.3, a series of pulses are generated from a rotating encoder wheel which closes an electric circuit, or not, depending on the location of raised contacts. For column A, no pulses are generatAustralia’s electronics magazine ed in this example, and all seven rows are blank. For column B, the first and last rows are empty, and five pulses in a row are generated. For column C, the pattern through the seven rows is offon-off-on-off-on-off and so on. You can see the modulation of the carrier wave at the bottom of the diagram. At the receiver end, an electromagnet brings an inked marker into contact with a paper tape each time a carrier is detected. Since the transmitter and receiver are not synchronised, there is some possibility that signal delays due to radio propagation conditions or mismatches in the printer speed will cause image distortion. Therefore, the image is printed twice, so even if distortion is present, there is a good chance it can still be read. There is a detailed discussion of using modern software and hardware to emulate Hellschreiber modes on modern equipment at siliconchip.com.au/ link/ab66 (see Fig.5) and videos showing them in operation titled “Hell Feldfernschreiber and 15W.S.E.b in use” at youtu.be/VDB7wmV7ekA and “Feld Hell, WW2 German Hell Feldfernschreiber” at youtu.be/Rs4YZv6s70g We published an article by Stan Swan on using Hellschreiber in our May 2005 issue (siliconchip.com.au/ Article/3062), which has quite a bit April 2021  17 Fig.6: a screenshot of swradio-8 decoding DRM from Voice of Nigeria (https://von. gov.ng/) on 15.120MHz. This software runs on Windows and Linux and supports HackRF, RTL-SDR using the RT820 chip and SDRplay SDR devices. more detail along with instructions on transmitting and receiving data yourself using a computer sound card. For further details, see siliconchip.com. au/link/ab67 ii) Broadcast digital radio and TV 1) DAB+ Digital radio broadcasting in Australia was tested from 1999 and introduced in 2009, using the DAB+ (Digital Audio Broadcasting) standard, as used in Europe (but not the UK & Ireland). In Australia, these are broadcast on VHF frequency blocks 8C (199.360MHz), 9A (202.928MHz), 9B (204.64MHz) and 9C (206.352MHz) in multiplexed form, with multiple radio stations per frequency block. At the time of writing, DAB+ broadcasts were predominantly in capital cities; and not all cities use all channels. Each frequency block occupies 1.536MHz and supports 1152kbps of usable data. Each radio station uses a different amount of data according to their requirements. Data rates of 24, 32, 40, 48, 56, 64, 80, 88 and 96kbps are used on Australian stations. At the moment, many of these stations are also simulcast on regular AM or FM bands. Using 3A Forward Error Correction at a “code rate” of 1/2 each frequency block, it can support 18 x 64kbps stations (1152kbps total), or more at a lower data rate. The DAB+ standard supports features such as Program Assisted Data (PAD) with text of up to 128 characters per segment, Slideshow (SLS) images, 18 Silicon Chip Electronic Programme Guide (EPG) and other data services such as traffic reports, location of fuel and price, etc. We published a series of detailed articles on DAB+ by Alan Hughes in the February, March, April, June & August 2009 issues (siliconchip.com. au/Series/36). We have also published two radios capable of receiving DAB+ broadcasts, most recently in the January-March 2019 issues (siliconchip. com.au/Series/330). For further information, see the PDF at siliconchip.com.au/link/ab68 2) Digital AM and FM broadcasts The most popular broadcast bands are AM medium wave (525-1705kHz), FM broadcast (87.5-108MHz) and to a lesser extent, shortwave bands (discontinuous between 2.3MHz and 26.1MHz). In the USA, Canada and Mexico, the proprietary HDR (HD Radio) system is used on the AM and FM broad- cast bands. HD Radio allows for either hybrid digital/analog broadcasts or digital-only. With hybrid broadcasts, regular AM and FM broadcast-band equipment can still receive the analog portion. As implemented in the USA, in AM or FM hybrid mode, analog and digital signals are broadcast on the same frequency. For FM, the bandwidth required for a hybrid signal is 400kHz, double their usual channel spacing of 200kHz. They have a wide channel spacing because stations that are close in frequency are geographically separated. Europe and Australia use a 100kHz channel spacing, making adoption of this system problematic. In the hybrid FM mode, data rates up to 150kbps can be transmitted along with the analog broadcast, while in pure digital mode, up to 300kbps is available, allowing features like surround sound. For AM, 20kHz channels are the standard (they use 10kHz channel spacing, while Australia and Europe use 9kHz). In hybrid AM mode, digital data is usually transmitted at 40kbps. In the AM pure digital mode, the full 20kHz channel width is used, giving 20-40kbps, although up to 60kbps can be achieved if 5kHz overlap into the adjacent channels is allowed. That could cause interference on adjacent channels unless there is sufficient geographical separation, and there could still be problems at night with large skip distances. In the USA, many car manufacturers offer subscriber satellite radio in their car receivers, and all majors offer HD Radio as well. Satellite radio is transmitted at 2.3GHz and offers nation-wide reception. Fig.7: a Samsung “Anycall” mobile phone from South Korea with hardware and software to receive DMB-T. This is an older model; there no longer appear to be phones available today with this feature. Source: Wikimedia user Ryuch Australia’s electronics magazine siliconchip.com.au 3) Digital Radio Mondiale (DRM) DRM digital audio broadcasting can be on longwave (as used in Europe), the AM and FM broadcast bands, and shortwave. As it is more spectrally efficient than analog modes, more stations can fit into the same bandwidth using the xHE-AAC digital codec (“codec” is an abbreviation of encoder/decoder). DRM30 is the mode used below 30MHz, while DRM+ is used between 30MHz and 300MHz. Other data can be transmitted along with the audio. Countries that use DRM include New Zealand, India, France, Brazil, China, Hungary, Russia, Romania, Kuwait, UK, USA, Singapore, Nigeria, and Abu Dhabi. ACMA is considering the possibility of its use in Australia – see siliconchip.com.au/link/ab69 We published a detailed article on DRM (not to be confused with ‘digital rights management’) in the September 2017 issue (siliconchip.com.au/ Article/10798). It is very suitable for use in sparsely populated areas, like much of Australia, because a low-power transmitter can serve a vast area. If you are interested in listening to DRM, and conditions and your antenna are right, you can try to pick it up in Australia. DRM signals abroad are not explicitly aimed at Australia, but it seems that New Zealand transmissions can sometimes be picked up. See the comments at siliconchip.com.au/link/ab6a and the schedules at www.drmrx.org/ drmschedules/ DRM can be heard by: • a radio designed to receive it, such as the Tecsun Q-3061 DRM Shortwave Radio (www.tecsunradios.com.au/ store/), certain WiNRADIOs with licensed software (www.winradio. com/home/drm.htm) plus models from Gospell, Avion and Starwaves • a radio modified to obtain a 12kHz IF signal for software processing • a radio with an existing 12kHz IF output for software processing • a software-defined radio (SDR) used in conjunction with the “Dream” software Software to receive HDR, DAB+ and DRM HDR, DAB+ and DRM can be resiliconchip.com.au Don’t pay $$$$ for a commercial receiver: this uses a <$20 USB DTV/DAB+ dongle as the basis for a very high performance SSB, FM, CW, AM etc radio that tunes from DC to daylight! Published October 2013 Features:  Tuned RF front end  Up-converter inbuilt  Powered from PC via USB cable  Single PCB construction Want to know more? Search for “sidradio” at siliconchip.com.au/project/sidradio PCBs & Micros available from On-Line Shop ceived on dedicated receivers or via a computer, sound card and appropriate receiver. • NRSC5 is multi-platform software that allows reception of HD Radio using an SDR – see www.rtl-sdr. com/tag/nrsc-5/ Note that as HD Radio is only broadcast in North America, it could only be received in Australia/NZ under extremely rare skip conditions. • To decode DAB/DAB+ signals, you can use qt-dab (siliconchip.com.au/ link/ab6b) for Linux and Raspberry Pi, or QIRX SDR (https://qirx.softsyst.com/ and www.welle.io) for Windows, Linux, macOS and Android. • swradio-8 (siliconchip.com.au/link/ ab6c) for Windows and Linux decodes DRM and many other modes – see Fig.6. • For a variety of digital radio opensource tools for DAB for Linux, see https://github.com/Opendigitalradio • Dream (https://sourceforge.net/ projects/drm/) is a software DRM decoder. Signals can be received with a modified analog receiver (SW, MW or LW) and fed to a PC sound card, but read comments at the link before trying to use it. See our detailed articles on this topic in the November 2013 and September 2017 issues at siliconchip.com.au/Article/5456 and siliconchip.com.au/Article/ 10798    More details are in the video titled “Decoding Digital Radio Mondiale DRM Using Dream Decoder” at youtu. be/lextsInwtUQ restrial Digital Multimedia Broadcasting) is a video and multimedia delivery service by radio on VHF and UHF bands. It is used in South Korea (Fig.7), Norway, Germany, France, China, Mexico, the Netherlands, Indonesia, Canada, Malaysia and Cambodia. See the video titled “Korean Mobile TV, DMB” at https://youtu.be/ 2kx92SZ4grU The ATSC-M/H (Advanced Television Systems Committee – Mobile/ Handheld) standard is used in the USA. The signals are broadcast in the digital TV spectrum, and it is an extension of the digital TV format used in that country. Fig.8: the VK3RTV transmission tower on Mount View in Melbourne. It is a shared tower, but the transmit antenna is at the very top, and there are three receive antennas covering onethird of the horizon each, just below the tower ‘outriggers’. 4) Mobile TV S-DMB or T-DMB (Satellite or TerAustralia’s electronics magazine April 2021  19 Fig.9: a screengrab of EasyPal from the video titled “EasyPal Digital SSTV 40m Band #Shortwave, 02nd January 2019, 1100-1120 UTC” at https://youtu.be/K0bcrnIB7sU About 65 TV stations transmit this format, although there don’t appear to be any phone-type devices that can receive it. 5) Digital TV Australia’s TV system is now fully digital, with the transition occurring from 1st January 2001 to 10th December 2013. We use the European DVB-T standard, although there are numerous variations within this standard including the codecs used, the number of sub-carriers, channel bandwidths and modulation schemes. The data stream is transmitted using coded orthogonal frequency-division multiplexing (COFDM). The precise details are beyond the scope of this article. You can see an overview of the standard at siliconchip.com.au/link/ab6x We published articles on digital TV in the March & April 2008 issues (siliconchip.com.au/Series/49), plus March 2010 (siliconchip.com.au/ Article/77), June 2013 (siliconchip. com.au/Article/3820) and April 2016 (siliconchip.com.au/Article/9903). Australia’s DTV system allows for high-quality video and sound, datacasting, video program information and a higher number of channels for a 20 Silicon Chip similar spectrum space than was possible with analog TV. The government is currently calling for submissions regarding reforming television in Australia including the technical standards. Submissions close very soon: 23rd May 2021. Go to siliconchip.com.au/ link/ab6d to find out more. In the USA, Canada, Mexico and South Korea, the digital TV standard used is ATSC. Japan uses its own IDSB standard, and several countries in Asia, South America and Africa have adopted it. (Does this remind anyone of the PAL/NTSC/SECAM mess?) Fig.10: a daily weather map from the BoM. This can be downloaded from www. bom.gov.au/difacs/IDX0854.gif For other maps from the weatherfax service, see the list under “Australian Weather Charts” at www.weather.gov/media/marine/ otherfax.txt (they don’t appear to be listed on the Australian website!). Australia’s electronics magazine siliconchip.com.au You can watch some live analog and digital SSTV streams at www. g0hwc.com iv) Analog slow-scan TV (SSTV) and radio fax These two types of transmission might initially seem to be digital, but both are transmitted by an HF or VHF analog modulated radio signal using the same bandwidth as voice. Like voice transmissions, it is possible to have long-distance or global reach under the right ionospheric conditions and frequencies. Of course, modern transmission and receiving equipment is likely to be digital, such as a computer, making these modes much easier and cheaper to work with. So we are including them here due to the extensive digitisation at both ends. The hardware requirements are modest, typically just needing an old PC with a sound card in addition to Fig.11: a screengrab of DroidSSTV from a suitable radio receiver (possibly an SDR) and antenna. a smartphone. The original way to view slow-scan TV was with a military-surplus long iii) Amateur digital TV persistence ex-radar CRT, where the image would stay long enough until 1) Amateur DVB-T broadcasts that part of the screen was refreshed Melbourne has a DVB-T amateur with a new image. This is unnecessary 200W TV repeater, VK3RTV (www. when the image is stored digitally in vk3rtv.com) at Mt Waverley, shown a computer. in Fig.8. You need to be a radio ham to transUnlike the SSTV modes mentioned mit SSTV, but anyone can receive both below, this operates at a full video frame rate, just like consumer digital TV. The signal can be received on some TVs or set-top boxes at 445.5MHz, or you can view live streams online from anywhere, according to the details on their website. You can view a recorded video of Amateur TV Net night titled “VK3RTV Net 05th January 2021 Off-air log [mixed quality, missing first 3 minutes]” at https://youtu.be/fNgK3B6ptr0 2) Digital slow-scan TV Strictly speaking, this mode is not slow-scan TV (see next section) because it’s digital, but the name has stuck. The late Australian Erik Sunstrup VK4AES developed a digital SSTV for radio amateurs known as EasyPal (Fig.9). Versions of his program are still available for download. For more information, see www.g0hwc.com/ sstv_drm_news.html siliconchip.com.au SSTV and weather fax. Radio fax is now primarily used to transmit weather information (weather fax) to ships at sea, but has been mostly replaced by other methods such as satellite transmissions. Nevertheless, several weather fax transmissions are active worldwide, including from North America, Europe, Asia and Australia (see Fig.10). Some useful radio fax links are: • a schedule of worldwide transmissions: siliconchip.com.au/link/ab6e • a schedule of Australian transmissions: siliconchip.com.au/link/ab6f • software to receive and decode weather fax on a PC: https://arachnoid .com/JWX/ • receive weather fax on your Android or iOS device: http://siliconchip. com.au/link/ab6g You will need an appropriate radio receiver. • interesting commentary on problems and sample images from the BoM: siliconchip.com.au/link/ab6h • video showing receipt of Australian weather fax titled “Weather Fax from Australian BOM HF radio transmission”: https://youtu.be/SxKn69JAuaE • receive SSTV on a PC: www. essexham.co.uk/sstv-the-basics • another popular SSTV receiver program for PC, MmSSTV: https:// hamsoft.ca/pages/mmsstv.php • a newer version of MmSSTV is called YONIQ: http://radiogalena. es/yoniq/ (in Spanish but you can Fig.12: HDSDR, popular free software for SDR radios although it only supports analog modes. Australia’s electronics magazine April 2021  21 v) Software-defined radios (SDRs) Fig.13: two self-contained SDRs: a Malachite SDR (left) and PortaPack H2 combined with Hack RF (right). Source: the video at https://youtu.be/ Ja6LTDf9wAk use a translator on the web page, and the program can run in English). • view SSTV images from the International Space Station on VHF 145.800MHz FM: https://amsat-uk. org/beginners/iss-sstv/ It is even possible to view SSTV on your phone by holding the phone next to a radio loudspeaker tuned into an SSTV channel with the right App. The App for iOS is “SSTV Slow Scan TV”. For Android, use “DroidSSTV - SSTV for Ham Radio”, shown in Fig.11. We haven’t tested either ourselves. These can be very cheap devices, available for as little as $20, that can receive various digital signals on your computer. Popular free software for doing this is HDSDR (Fig.12), SDR Console, SDR# (see our article in November 2017; siliconchip.com.au/ Article/10879), Linrad, SdrDx, Gqrx SDR, and SDR Touch. If you plan to buy an SDR dongle, make sure its chipset is compatible with any software you intend to use. Besides the November 2017 issue, we have published multiple articles on SDRs, including two projects to build your own. The following issues and articles are relevant: • LF-HF Up-Converter For VHF/UHF Fig.14: a screengrab of fldigi in action. 22 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.15: an image received by US radio amateur KD8TTE from Shortwave Radiogram (https://swradiogram.net/). Digital TV Dongles, June 2013: siliconchip.com.au/Article/3810 • SiDRADIO integrated SDR, October & November 2013: siliconchip.com. au/Series/130 • More Reception Modes For SiDRADIO & SDRs, December 2013: siliconchip.com.au/Article/5629 • Tunable HF Preamp for SDRs, January 2020: siliconchip.com.au/ Article/12219 • New wideband RTL-SDR modules, May & June 2020: siliconchip.com. au/Series/306 Self-contained SDR radios with inbuilt software and a display can also be purchased or constructed – see Fig.13. You can try your hand at receiving digital radio with a communications receiver or SDR and appropriate software. There are a large number of software packages, due to space we will just look at one. “fldigi” is a free and popular software suite for digital radio modes (see Figs.14-16). It can transmit or receive digital radio when connected to a transceiver, although you need to be a ham or commercial radio operator to transmit. The software runs on many types of PCs and other computers; even the Raspberry Pi. It supports many general and ham radio digital modes such as Contestia, CW, DominoEX, FSQ, Hell (for Hellschreiber machines), IFKB, MFSK, MT63, Olivia, PSK, RSID, RTTY, Thor and Throb. It is available for download at www.w1hkj.com and https:// sourceforge.net/projects/fldigi/ There is a detailed 576-page PDF user manual at http://siliconchip.com. au/link/ab6i and a comprehensive collection of spectra and the sounds of various digital modes at www.w1hkj. com/modes/index.htm In the United States, this software is used by various emergency management services for communications during natural disasters. Shortwave broadcasters such as Radio Australia (before they became an online-only service) have experimented with digital modes using this software. Shortwave Radiogram (https:// swradiogram.net/) is a radio show by Dr Kim Andrew Elliott KD9XB that transmits digital text and images via shortwave radio. It can be decoded with fldigi, TIVAR or AndFlmsg on Android devices. We have seen various reports that it can be received in Australia. For tips on receiving Shortwave Radiogram, see siliconchip.com.au/link/ ab6j and the videos titled “Receiving Shortwave Radiogram – A Digital Text and Image Shortwave Broadcast” at https://youtu.be/0mNgGnvjzVs and “Shortwave Radiogram 170, 20th September 2020, 7780 kHz, 2330-2400 UTC” at https://youtu.be/ Stt4C8Rwu18 For an extremely comprehensive guide to what various digital mode signals sound like and look like in spectrograms check the following links: siliconchip.com.au/link/ab6j siliconchip.com.au/link/ab6k http://m0obu.net/digital-modes.html There is a comprehensive list of other software packages to receive digital modes at www.qsl.net/rv3apm/ (it is not clear if it is entirely up to date) and http://siliconchip.com.au/link/ab6l NEXT MONTH: In Part 2 of this feature, Dr David Maddison will look at more of the digital modes in use today and the promSC ise of things to come! Fig.16: some digital modes as they appear on the fldigi waterfall display. Source: Summerland Amateur Radio Club (https://sarc.org.au/fl-digi/). siliconchip.com.au Australia’s electronics magazine April 2021  23