Tuesday, November 30, 2010

Feld Hell Contesting at KD8JHJ

On November 20th I participated in the Feld Hell Club's monthly 2 hour sprint.  It has been a while since I got on the air using one of my favorite digital modes called Hellschreiber.

Hellschreiber, or Feld Hell as we call it in ham radio didn't start out as a digital sound card mode.  In fact it's been around for 80 years and only in the past 20 years has the technology been adapted into amateur radio software and allowed us to use this early forerunner of the fax machine in our radio exploits.

So what's with the funny name?   

Rudolph Hell (1901-2002)

Rudolph Hell was born on December 19, 1901 in Eggmuhl, Bavaria.  His father was the station master of the town's stop along the Bavarian State Railway.  Obviously young Rudolph was exposed to Morse Code then the pinnacle of communications technology.  As he successfully progressed through school he knew his future lay in electrical engineering.   Hell attended university at the Munich Technical College.

By 1930 Hell had started his own business and developed a system called the Hell writing telegraph.  This electro-mechanical device broke down text into dots for transmission then reassembled the data into readable text at the receiving end.  In time the system was refined and found to be suitable for radio communications. By 1934 this technology was in use by news agencies and by the end of World War Two more than 50,000 units had been produced.

Hellschreiber works by dividing a line of text into columns in which each column is 7 pixels tall. the data is then transmitted from the bottom pixel up.  Black pixels are transmitted as a signal and white pixels are sent as silence.  This takes place at a speed of 122.5 baud.  Because the incoming text was printed out on continuous paper rolls the number of columns a message could contain was indefinite.  

Take a close look at the screen shot I made during the Feld Hell Contest at the top of my post.  Pictured are both my transmissions and those of WB2HTO.  They are easy to differentiate because we each have a different font style selected in our software.  The original Hellschreiber machine printed the incoming message onto a narrow paper strip that was adhesive backed.  the message could be transcribed by hand as shown in the picture below or the strips could be cut and assembled onto a sheet of paper like a telegram.

As a modern digital mode Hellschreiber is unique in several ways.  The incoming text feeds onto the screen from left to right at a speed that I imagine is very close to that of the original mechanical print head. This preserves the look if not the feel of the original Feld Hell mode.  Once the screen is full the uppermost strip disappears as the next line begins printing at the bottom.

Because Feld Hell is based on Facsimile it does not suffer certain conditions that plague the other sound card modes. Other digital modes employ forms of error correction to counter the negative effects of  atmospheric conditions and weak propagation.  The software does the best it can to decipher the received message but often the text is garbled or characters are missed completely.  With Hellschreiber there is never a missed character or annoying misspellings caused by the error correction.  Again the screen shot shows WB2HTO's signal to be strong and clear -nearly solid black on a white background.  If the incoming signal is very weak or propagation is not favorable the signal will show up on an increasingly gray background.  Notice on the top line is a section of gray space between each of our transmissions.  This is just the static present on the frequency while neither of us is transmitting.  A weak signal can be so faint that it blends into the gray "noise" and may be only partially visible or not at all. 

Hellschreiber prints all of the received columns twice one on top of the other.  This is done to make up for small timing errors that can be present in the equipment.  The text can print like WB2HTO's two identical lines or like mine with one readable line of text in the middle with the other line split some on the bottom and the rest on top.  The print can also be slanted running off the "strip".  Regardless enough characters are present to get the message copied complete.

It's the fascinating history behind this mode that makes it one of my favorites.  
Although this post deals with Feld Hell,  patented by Hell in 1929 this man's contributions to information technology as we know it today are amazing.  Here are some of Rudolph Hell's inventions and innovations:

1925  Hell and Max Dieckmann invented the scanning tube.  The first step in developing the ability to break a picture down into dots for transmission.

1927  Hell invents the first radio location device for aviation.  For the first time in history aviators could fly through inclement weather and find their way to a destination by following radio beacons.

1950-60s  Hell developes the Digiset.  A virtual "typeset" of electronically produced characters.  For the first time in  500 years since Gutenburg invented moveable type and the printing press, the three dimensional letters which had always been physical objects in a typecase were now electronic symbols broken down to dots and stored in a computer for use as needed. 

1960's Hell invents several prepress systems that revolutionized the graphic arts industry as well as color scanners, faxes and engraving machines. 

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