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Granddad’s 1930s text messaging? hellschreiber Data over UHF CB Younger readers may be unimpressed with yesteryear’s quaint technology but during the golden age of radio, beside such local 1950s staples as “Life with Dexter” and “Dad and Dave”, considerable international communications came via wireless signals on the adjacent short wave bands (3-30MHz). Gasp – you mean no global roaming text messaging? by Stan Swan siliconchip.com.au May 2005  41 Y and a chain-sawing woodpecker and es – pre TV, FM, satellites, GPS no doubt prompted many a spouse or (and certainly WiFi, mobile mum to hit the mains switch. phones, internet and email) things were pretty tough on the elecHellschreiber tronic communications front. Perhaps the most enduring of However that did motivate many, these short wave data signals was a myself included, to explore the tech1929 invention by Dr. Rudolf Hell nological magic then represented by (1901–2002!), known as Hellschreiber radio. Numerous ham radio and elec(German – Dr. Hells “bright writing”). tronics careers began when curious Aside from his engineering genius, youngsters twiddled the dial on the which also covered early TV and an family wireless and wondered how aircraft autopilot, Dr. Hell (just his the sound reached them from the other surname – nothing satanic!) was a side of the world. shrewd businessman and benevolent Along with such diverse short wave employer, with eventually some 2000 voice stations as the Voice of America staff in his German factories making and the BBC News, a huge volume radio gear, fax machines, scanners of powerful commercial, embassy, A 1940s era portable “Feld-Hell” and commercial printing presses military and news service information transceiver, as used by the (Linotype/Heidelberg) . passed as hideously sounding pulsed German army throughout WW2. On his 100th birthday in 2001 his data traffic over these bands. Tuning weak foreign stations amongst the cacophony of grateful hometown of Kiel (in northern Germany) even sounds that represented SW listening at that stage was often renamed a street “Dr-Hell-Strasse” in his honour. Hellschreiber is a form of 1-D fax and although ancient, an frustrating but entertaining experience, compounded by atmospheric static crashes, propagation fades, heterodyne is still considered (along with Morse Code) one of the most whistles, deliberate jamming interference and – oh yes – effective techniques for sending text information in weak or noisy signal conditions – both wireless and landline. analog dials. And you thought video games were noisy! However, unlike audible Morse decoding (which also It often sounded like a cross between an orchestra tune up Here’s a screen grab for the IZ8BLY Hellscreiber sound card software. 42  Silicon Chip siliconchip.com.au needs a trained operator), “Hell” uses 56kbps dial-up modems but simplicity the outstanding ability of our human and robustness ensure this narrow bandeye and brain to recognise shapes and width mode remains durable. distorted patterns. Sound card software Instead of deciphering with your ears, Hell is decoded as an image with With war surplus equipment just your eyes, via its signals traditionally a memory for most old timers and as printed out as characters on paper even post-war commercial equipment ticker tape for anyone who can read was scrapped in favour of modern datato understand. comms, Hellscreiber became a technology Also, the printed copy allows later that time almost passed by. consideration of confused noisy mes- It’s not every living person who has a In the early 1980s however radio hams sages - misheard Morse characters street named after them. Dr Hell had! began experimenting with fully elecmay be lost forever. tronic implementations, although these Such eye/brain data decoding has lead to Hellschreiber were not for the faint hearted. being in fact recently titled as a human readable “fuzzy The whole wireless data field however underwent an mode” – neither quite analog or totally digital. enormous upsurge only some six years ago, as cheap PC Hellschreiber became very popular in the 1930s, at a hardware and sound cards became well established. time when teleprinters were complex and costly, since it When combined with ingenious software, the PC sound allowed direct keyboard text transmission on machines that cards inbuilt digital signal processing features can offer near were cheap and reliable with few moving parts. effortless external data encoding and decoding. Its most celebrated use however came during WW2 with Such has been the phenomenal uptake of this approach, the German Army, when field portable electromechani- especially with radio hams on their short wave bands, that cal “Feld-Hell” units often were the only viable wireless brand-new weak signal data modes (CLOVER, PICCOLO, communication link under battle conditions and enemy PSK etc) have recently evolved, some even allowing fully jamming. digital Slow Scan TV (SSTV) images to be sent via low Such a character-forming tradition ensured wide sub- power HF radio transceivers around the world. sequent peace-time use, with commercial short wave Naturally such offerings are appealing for isolated services employing the mode for decades afterwards well communities or seafarers and of course emergency use – into the 1980s. Even SONY once made suitable units ubiquitous Internet cafes and mobile (cell) phones may under licence. be early casualties in disasters such as the recent Indian Ocean tsunami and earthquakes. Hell basics Although it’s now fully electronic and can be enhanced with sub modes such as FM-Hell, classic Hellschreiber involves on/off keying that portrays each text character (only capitals are used) as a series of vertically delivered dot pixels in a 7x7 matrix. In effect the outgoing keyboard characters are broken into a string of dots and then suitably reassembled at the receiver. Two identical lines are displayed so that legibility remains with even major errors and blank spaces and gaps between characters are also considered, as are half height pixels to increase resolution. Here’s a capital E, with tones black and silence white- Hell’s been rediscovered! Although perhaps best employed at lower frequencies 7 6 ! ! ! ! ! 5 ! 4 ! ! ! ! 3 ! 2 ! ! ! ! ! 1 1 2 3 4 5 6 7 Traditionally 150 characters were transmitted a minute, with each taking 400ms. This equates to 2½ ch/sec or about 25 “PARIS” words a minute – a comfortable typing speed for many! With 7x7 (49) pixels a character, each pixel duration is .4/49 = 8.163ms, so the data rate is 1/8.163ms = 122.5bps. Naturally this is very pedestrian beside even today’s siliconchip.com.au Close-up of a classic electro-mechanical Hellscreiber. Note the paper tape under the keyboard. May 2005  43 The human eye and brain combine for enhanced image decoding, allowing characters in “noisy” messages to be distinguished. when no other link is feasible, it’s now very easy to experiment with Hellscreiber over licence-free UHF CB. Enhanced modes, such as FM-Hell, offer great weak signal performance on even cheap CB sets– especially if used in conjunction with range-boosting antenna as outlined in the January 2005 SILICON CHIP. Virtually any old Windows PC and sound card will do, since even a Win98 slow-coach laptop will readily keep up with the slow data employed. Naturally other transceivers and approved bands can be used if suitably licensed, with the old 27MHz CB band particularly tempting. Software – what’s involved? Shareware Hellschreiber sound card software abounds, (Google “Hellschreiber”) with V4.0 of “IZ8BLY” by Italian ham Nino justifiably considered outstanding. In addition to classic Feld-Hell (and even Morse), it offers many enhanced modes, with the bolder characters and impulse noise immunity of FM-Hell particularly appealing. For extreme conditions, even meteor scatter and ultra- The IZ8BLY software will also allow normal Morse code to be sent and received. Messages can be “read” from the width of the bars, with a short “dit” visibly thinner than a long fatter “dah”. Hence SOS .../---/... slow modes are available. Screen data can be saved as a .bmp snapshot & then printed, although if emailing images you would first convert them to a smaller .gif file. The PC screen display can’t be taken as straight text to a spreadsheet or graph however. It’s an image, remember! Once downloaded (~1MB) and installed, you may only need to just start typing if you’ve two nearby sound card PCs both set to use the same mode. Such is the robustness of this technology that with suitably adjusted mic & speaker levels, even exchanging data as audio signals across a small room will usually be enough to display characters on the second PC – hard walls will show up as ghosted reflections. Modern switched-tone Hell implementations are quite musical incidentally, although the classic WW2 mode sounded “scratchy”. Although direct audio is an entertaining party or classroom trick, for proper wireless links simply turn on each UHF CB transceiver, set to a data channel and enable VOX (voice activated switching). Suitable sound card mic/speaker and CB volume ad- (Left, above:) Jaycar and DSE both stock handheld UHF CB’s that are typical of the cheap sets now on sale. Their units sport a multifunction socket for external mic and earphone connections, allowing easy acoustic coupling with a laptop’s mic and speaker by positioning CB mic to PC speaker and vice versa. For more professional linking a wired connection, simply made with 3.5mm stereo phono plugs, is preferable (and quieter!). (Right:) Positioning, perhaps by Velcro, headset mic to PC speaker and headphone to PC mic will allow easy acoustic coupling but you’ll hear the musical tones and room noises may corrupt data. 44  Silicon Chip siliconchip.com.au TO PC SOUND CARD INPUT TO 477MHz UHF CB CHANNEL 22 OR 23 SET TO “VOX” (eg, JAYCAR DC-1030, DICK SMITH D-1793, etc) POSSIBLE 3.5mm to 2.5mm ADAPTOR TIP SLEEVE RING TIP POSSIBLE LIMITING RESISTOR (~330kΩ) RING SLEEVE Three 3.5mm stereo plugs can be easily wired to connect the CB set to a PC soundcard, and as well as Hellscreiber may suit other soundcard digital modes as well. To save wiring a fiddly 2.5mm plug, just use a 3.5/2.5mm adaptor if using the DSE sets and even consider sacrificing a cheap headphone set for its flexible cables and single prewired plug. You may need to experiment with the dropping resistor value, CB volume and sound card settings. justing will usually be enough to trigger the transmitter, although naturally volume levels may be rather loud unless you place the CB speaker very near the PC mic. For more elegance, it’s suggested you use the headset and mic combo that is now available for most budget CB sets. These usually position nicely above the inbuilt mic and speaker of a laptop and allow much quieter acoustic coupling – Velcro or Bluetak assist in securing the PC mic to the CB speaker and vice versa. However for extended use room noises may interfere and the faint data tones may be annoying, as also may the PC SOUND CARD I/O TIP SLEEVE RING (NC) TO PC SOUND CARD OUTPUT MIC LINE TIP SLEEVE RING (NC) SPKR disabled background squelch noise if monitoring weak signals. Cable connection Direct cabling of two budget CB handhelds (DSE D-1793 & Jaycar DC-1030) was investigated and although these sets differ in their I/O socket size they were found electrically similar and readily converted with 2.5-3.5mm adaptors. To ease soldering woes on the 3.5mm stereo plug, a budget stereo headphone could be sacrificed for its shielded coaxial leads and CB plug pre-wiring. Such a cable allows a completely silent electrically-coupled connection direct to the soundcard but audio levels will almost certainly need tweaking on both your CB set and PC. Experimentation with a Toshiba P-233 480CDT laptop showed optimum Feld-Hell connection to its soundcard mic input was via a 330kW series resistor. FM-Hell however, being very impulse noise immune, behaved well on both the mic and line inputs without this limiting resistor. Applications Since anyone with suitable CB and PC sound card software can join in, it’s feasible for a UHF Hell chat room to evolve, suiting perhaps a scout or school group. Nino’s free software is not intended for commercial use however, so using it to co-ordinate big game fishing, courier deliveries, gas field exploration and the like may be frowned on. Perhaps the best use might be delivering weak telemetry data for an educational project – much as initially envisaged the UHF CB channels 22 and 23 would be suited for. Data images will eventually scroll off the screen top after a few minutes unless paused but the IZ8BLY software includes macros that may assist. Mmm – fancy a challenge? I wonder if a suitable Picaxe could be persuaded to generate Hell! SC References and web links: IZ8BLY software: www.geocities.com/iz8bly/ For convenience these are hot linked at www.manuka.orcon. net.nz/hellrefs.htm siliconchip.com.au May 2005  45