转自：
http://www.eham.net/articles/11472一种挺有意思的数字通讯模式。
hellschreiber -- the forgotten mode
scott schultz (n0iu) on july 20, 2005
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john wa6bfh has inspired me. he has a passion for particular bands and is not shy at telling people about them and encouraging people to use them. one of my passions are the digital modes. in particular, i enjoy hellschreiber. like 220 mhz, there is precious little activity on this mode. but unlike 220 mhz where you will need to buy dedicated equipment, if you are already using other soundcard-based digital modes, it will cost you nothing to try this mode since there are two popular software packages available for free!
hellschreiber is a german name, meaning "bright writing", or "clear writing". hellschreiber is anything but a new mode. it was first patented in 1929 which makes it the oldest machine generated data transmission mode used in amateur radio. to put this in perspective, ssb was not introduced to the amateur radio community until 1948! like it's younger cousin rtty, hellschreiber was originally a land based method of transmitting information and was later adapted for radio transmission. also like rtty, this mode is experiencing a resurgence in popularity due to the recent development of computer software used in conjunction with a soundcard which has taken the place of cumbersome mechanical devices which were originally required to use this mode.
if you are not interested in learning how this fascinating mode works, then this will be a very short article. if you are already using psk31 or any of the other sound card based modes, all you need is the hellschreiber software.
one program is from nino porcino iz8bly and can be found at:
http://www.geocities.com/iz8bly/hell/index.htm.
this program only does the various flavors of hellschreiber. the website also includes links that go into detailed theory of this mode.
another popular choice is multipsk. don't let the name fool you. not only does it do psk31, it also does just about every other soundcard-based mode known to man, including the various flavors of hellschreiber including a faster version called hell80. the latest version (v3.9) can be found at:
http://members.aol.com/f6cte/index_anglais.htm.
now to the theory -
in order to transmit information from point a to point b, it has generally been thought it had to be done in either an analog or digital format. modes such as phone, voice and even cw are analog while modes such as rtty and psk31 are digital. by definition, when something is put into a digital format, it is put into a binary or two-state format. also, there must be some sort of interpreting mechanism on each end to convert the data into digital signals and vice versa. the mechanism (usually a personal computer with appropriate software and hardware, i.e. a sound card, multi-mode controller or tnc) takes the analog data (the words you type on the keyboard) and converts it into distinct audio tones which are fed into your radio. on the receiving end, this process is reversed. the software converts those tones into characters which are displayed on your screen. to be considered truly digital, data must also be coded. this means there are other bits of information wrapped around the text that synchronize the information and tell the receiving mechanism where each letter begins and ends. there are many schemes for coding data in order to (hopefully) assure it will be received properly.
but the transmission of information does not necessarily fall neatly into one of these two categories. in between there are uzzy?modes and hellschreiber is one of those fuzzy modes. why is it called fuzzy? perhaps because the definition is unclear and it leaves many people scratching their head! the basic definition of fuzzy states that the data is machine generated (as with all other digital modes), but the output is intended to be readable only by a human. so how is this different from rtty or psk31 which also displays human readable characters on the screen? the main difference is that fuzzy transmissions must be uncoded; without any synchronization or error correcting data wrapped around the information. that is the subtle but crucial difference.
with psk31 and rtty, you are presented with the actual computer generated characters (ascii characters or resident fonts) which are the result of complex de-coding algorithms which are specifically meant to be machine readable. you as the human do not have to decide what character was being sent; the software does its best to do that for you. hellschreiber, however, just paints pictures that represent characters which are specifically not machine readable. in other words, the hellschreiber program is merely drawing a picture on your screen and it is up to you, the human, to look at the pixelated image and decide what character it is. the bottom line is that it is the human that makes the final character recognition determination in the fuzzy mode, not the computer. another example of a fuzzy mode is slow scan tv. while the image being sent is generated by a machine, the computer on the receiving end has no idea if it is drawing a picture of a sail boat or the operator's dog! as with hellschreiber, only the human looking at the screen determine what is being drawn on the screen.
so is the fuzzy mode better than digital? when using a digital mode and there is a loss of signal quality through natural noise like lightning or static (qrn), interference from closeby stations (qrm) or fading (qsb), the end result is garbage on your screen. why? if any piece of the complex digital puzzle is not received exactly as it was transmitted, the coding information can be lost along with the actual data and this confuses the computer. when this happens, the software makes its est guess?at what character it thinks it should be and it is usually wrong! with hellschreiber, it is impossible for the software to display an incorrect character on the screen since there is no interpretation of the incoming data as to what that data represents. so how does it handle interference or fading? one can tell the quality of the signal by the relative darkness of the pixelated characters on the screen. by using this grey scale method, a solid s9 signal would yield nearly solid black print and a weak signal would result in very light print. when the signal is too weak to copy, the characters just fade away to nothing.
here is an example of what hellschreiber looks like. this is a screen snapshot from the iz8bly program. you will see that the bottom half (where the other station is talking to me) is what ess than perfect?copy looks like. it may look fuzzy, but is still readable.
this article is just meant to be a teaser about this mode. for more detailed information about the fuzzy modes and how they relate to ham radio, check out murray greenman's site at
http://www.qsl.net/zl1bpu/ 73,
de scott n0iu
