Posts Tagged ‘typewriter’
From Backblocks To High Seas
I came across this great piece of history via the Google+ page of Cristian YO8TNB and had to share it here for others to enjoy. I have a soft spot for New Zealand, being so close to my country of birth, and I particularly noticed the carefully cultured accent of the announcer. On a more serious note, this video is an invaluable record of the wired and wireless technology used in 1939 and the procedures for transmitting a message from land to sea.
Hellschreiber and microprocessors – Bridging more than 80 years
ZL1HIT (Bryan Rentoul) has bridged a gap of more than 80 years by combining the text transmission system developed by Rudolf Hell in the late 1920’s with current microprocessor technology.
|A sample of received Hellschreiber test from Bryan’s beacon|
Hellschreiber sends a line of text as a series of vertical columns. Each column is broken down vertically into a series of pixels, normally using a 7 by 7 pixel grid to represent characters. The data for a line is then sent as a series of on-off signals to the receiver, using a variety of formats depending on the medium, but normally at a rate of 112.5 baud.
This process was historically accomplished with mechanical equipment but there are very few examples of this equipment still in operation and it is now sent and received by computer. Hellschreiber is very tolerant of noise and interference and requires only simple transmitters and receivers to work effectively.
|German Hellschreiber unit in operation|
With a microprocessor generating the digital on-off signals a simple crystal oscillator transmitter can be used to form a beacon station, one that transmits a call sign and perhaps some other information over and over. Changing the transmitted message is as simple as reprogramming the microprocessor or having it respond to a connected input, for Eg. A thermometer, light sensor, switch, etc.
Receiving the signal and decoding requires a radio receiver capable of CW reception and a computer running any of several free software packages like FLdigi or Digital Master 780.
|The ZL1HIT beacon using a PIC microprocessor and a simple crystal oscillator transmitter.|
For more information and the PIC microprocessor source code please visit the web page of Bryan Rentoul here : ZL1HIT Hellschreiber / PIC Beacon