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hellschreiber - revisited Regular readers will recall Stan Swan’s enthusiastic “Hellschreiber” feature back in the May 2005 issue of SILICON CHIP. It attracted a lot of interest and correspondence – not all of it 100% positive! First of all, a brief recap for those who might have missed it. Stan talked about the “rediscovery” of this WWII-vintage communication system, actually used to great effect by the German army with their portable “Feld-Hell” electromechanical units. In some ways, Hellschreiber may be thought of as a forerunner to modern-day facsimile machines, since it writes an image to paper. However, it was/is limited to transmission and reception of letters/numbers. Stan talked about the free Hellschreiber software available on the ’net and then went on to describe how it could be used on the “data only” channels 22 and 23 of the Australian UHF CB radio system, along with a suitable computer and sound card. Whoops! What Stan didn’t realize at the time was that the “data only” channels are restricted to absolutely miniscule amounts of data – three seconds maximum in each hour. This is much less than Hellschreiber requires. We only twigged to this ourselves when several readers (presumably users of the data-only channels!) wrote in to tell us of the transgression. Item Channel 6 22 23 Carrier Frequency (Megahertz) 476.950 476.975 It’s not mentioned at all on the Australian Communications Authority (ACA) website Class Licencing page (http://internet.aca.gov.au/ACA INTER.65650:STANDARD:pc= PC_1265). In fact, you have to go right back to the ACA’s “Radio Communication (Citizen Band Radio Stations) Class Licence 2002” page (http://internet.aca.gov.au/acainterwr/aca_ home/legislation/radcomm/class_licences/cbrs.rtf), then wend your way right through to Schedule 1 (CB station operational requirements) and finally work your way down to Section 6(g), before you find the specific reference to Channels 22 and 23 having a time limit. Phew! No wonder people don’t know about it! Moreover, those regulations, reproduced below (with the relevant clause in italics), don’t even mention the limitation to “telemetry and telecommand” – something Hellschreiber definitely is not. (Telemetry and Tele-command are digital signals, transmitted from one UHF CB to another, designed to either do something or read something – such as open or close an electronic gate lock or measure the water level in a dam on the opposite side of the property). To find those limitations, you need to go back to the Class Licencing Page mentioned above and . . . oh yes, there it is – Telemetry and Telecommand. Therefore, we must warn UHF CB users that, despite their being no licence requirements for their operation, there are most certainly regulations which have to be obeyed and the authorities could take a very dim view of people tying up the data channels with such things as Hellschreiber or even SSTV. (Stan had also been toying with the idea of using UHF 22/23 for SSTV but following our advice has shelved that idea, too!) There was one other small oversight in the Hellschreiber article. Stan supplied a photograph of a Hellschreiber transceiver (which we published on page 42 of that issue), which he had obtained from an obscure site on the ’net (good old Google!) and he‑ could not determine who, if anyone, owned the copyright. However, it seems that the photo in question may have itself been copied from the website of another NZ ham, Murray Greenman, ZL1BPU, who was not happy that he was not acknowledged as the rightful owner. To be honest, had we known about an original version of this contentious photo (http://www.qsl.net/zl1bpu/ FUZZY/History/fh44.jpg) we would have asked for permission to use it instead because it is of significantly better quality than the one Stan gave us and we actually printed! In any case, we apologise to Murray Greenman for the apparent inadvertent use of his photograph. SC Restriction A transmitter employed in a CB station: (a) must operate with a transmitter power not exceeding 5 watts; and (b) must not exceed an EIRP of 8.3 watts; and (c) must operate with an occupied bandwidth not exceeding 16 kHz; and (d) must not exceed a carrier frequency error of ±3 kHz; and (e) must not exceed an adjacent channel power of –22 dBm; and (f) must not exceed a conducted spurious emission of –30 dBm; and (g) must operate on a duty cycle of not more than 3 seconds in any period of 60 minutes; and (h) must be fitted with a device that shuts the transmitter down after 3 minutes of continuous operation. A receiver employed in a CB station must operate with a conducted spurious emission not exceeding –57 dBm. Note: The use of single frequency store and forward repeaters is permitted. 102  Silicon Chip siliconchip.com.au