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Hell in Space



You may remember that I've experimented on AO-10 using PSK31.  Recently, I
tried a very diffent mode:  Hellschreiber.  The most simple form, called
Feld-Hell, uses on-off keying to draw dot patterns of letters on the
screen.  It's sort of like a dot matrix printer or a stock ticker.  

"Hell" is a fuzzy mode, meaning that the computer does not decode the data,
but simply transforms it into a form readable by the human eye.  It is the
pattern-matching ability of the eye and brain that does the actual
decoding.  For further details, see Murray, ZL1BPU's web site at:

	http://www.qsl.net/zl1bpu/

Murray's site provides a link to download free Hellschreiber software,
including an excellent program written by Nino, IZ8BLY for Windows and a
sound card.

Now, all this is very "retro."  Hellschreiber was invented in 1929!
However, Feld-Hell's tuning requirements are nowhere near as stringent as
PSK31.  Since Feld-hell uses on-off keying, it shouldn't hog the
transponder.  So I wondered what its performance would be on AO-10.  

I ran some tests on 14 April.  Feld-Hell is not as sensitive as PSK31, so
it doesn't work as far out in the orbit or as deep into the worst QSB.  But
it also isn't nearly as frequency-sensitive as PSK31.  So you can use it on
AO-10 with occasional, rather than constant tuning.  And since it's an
on-off keying mode, Feld-Hell isn't a power hog and should be OK to use on
satellite. It really shows visually what is going on with the signal.  

Working myself with Feld-Hell, copy was excellent out to 17,000 km  with
only 35 watts of power, using ~11 db (10-foot long) CP Yagis.  Copy was
still quite good out to 27,000 km with 90 watts.  

At 33,000 km range, cyclical QSB was terrible, with the signal disappearing
for several seconds at a time.  The IZ8BLY software allows you to slow the
Feld-Hell signal to 1/4 or 1/8 of normal speed.  1/8 speed is about one
character every 3 seconds. Though this is excruciatingly slow, 1/8 speed
provided usable copy through the fades.  

At 37,700 km range, the QSB put big "holes" in the copy even at the slowest
speed.

I have some small JPEG files that show what copy was like at these ranges.
If anybody is interested, I can email them (sorry, I don't have a Web page
at present).

Bottom line is that Feld-Hell can give similar performance to ordinary CW
at medium AO-10 altitudes.  Near apogee, slow CW with very narrow-bandwidth
receive DSP filtering is better.  PSK31 is better than either, BUT you have
to tune constantly.

If anyone is interested in an AO-10 contact using either Hellschreiber or
PSK31, please email me.  It might be interesting to try Feld-Hell on a LEO
satellite, too.

Hope this is of interest!
73 from KD7MW,

--- Peter
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/ b b ,| ,| ,| ,|  ,| ,|  '  ,|   | ,|   |__|__|__|   |__|   |  |   |  |
                                ~'                            ========= 

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