Message-ID: <3C01071D.34B4F3AC@att.net>
Date: Sun, 25 Nov 2001 09:58:37 -0500
From: "Dexter McIntyre W4DEX" <dmcintyre@att.net>
Organization: JDM Communications
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RTTY on 73.3 kHz?
References: <4f.14ca23c4.293040de@aol.com> <007401c174d6$fc38f8a0$a3ca28c3@ericadodd> <001501c174ec$f212b260$0300a8c0@charter.net> <000201c1751b$6063bb00$3dce28c3@ericadodd> <3C000DE3.AED73455@att.net> <3C0011CB.3156569C@att.net> <001d01c175b1$0b29bb30$0400000a@parissn2>
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I lost all signal from the 73.3 kHz RTTY station by 0100 UT last
evening.  QRN was very high so the signal could have been just below my
noise level.  Relative signal strength logged are as follows:

2100 UT -52   dbm
2300 UT -48   dbm
0000 UT -47.5 dbm
0100 UT  undetectable
0200 UT      "
0300 UT      "
0400 UT      "

Bob, K3DJC, in Pa. also was hearing the signal.

I will be looking for the signal again.  I don't recall hearing it
before but when listening for G3AQC the receiver was in 20 Hz IF mode so
I would not have heard the RTTY.

73,
Dexter

Stewart Nelson wrote:
> 
> Dexter McIntyre W4DEX wrote:
> 
> > Just for grins, I recorded a 15 sec .wav file of the 73.3 kHz RTTY
> > signal and uploaded it at:
> >
> > www.qsl.net/w4dex/73khzRTTY.wav
> 
> > It sounds strong enough I almost believe it would print here
> > if the static crashes were absent.
> 
> Many thanks, Dexter, for the great puzzle.  Unfortunately, I failed
> miserably trying to solve it.  Although this is an FSK signal,
> I don't think it is RTTY in the usual sense.  Does anyone know the
> format (or at least the source)?
> 
> The apparent baud rate is 74.99; of course this is affected by the
> sampling rate of Dexter's sound card.  The frequency shift is also
> very close to 75 Hz, but I don't believe that it's precisely one
> carrier cycle per bit time, because attempts at coherent detection
> were unsuccessful.  However, even with a time-between-zero-crossings
> detector, the S/N was quite good (with aggressive predetect filtering).
> I considered a bit questionable when its frequency offset was less
> than 40% of average; only one of 1142 bits failed this test.
> So I'm confident that the data is nearly correct.  Unfortunately,
> I couldn't find any start or stop bits, any sign of a character
> length, any repeating patterns, or any other indication that it
> is anything but random.  I suspect that this data is compressed,
> encrypted, uses ECC, or perhaps all of the above.
> 
> If you can make any sense of the message below, let us know. "X"
> might be one or zero, "." is the opposite.
> 
> ...X.XX.X.XX..XXX..X.XXX.X...XX..X...X..X...X.X..XX...X...X....X...XXX..
> X..XX.X..XXX.X.XXX.XXX.XX..XX.X.X.XXXXX.X.....XXXXX...X.....XXX..X.XXXXX
> .XX.X.X.XXX...XXXXX..XX..XX..XXX..X.X.XX.X.X.XX......X..XXX..XX.XXXXX..X
> ...XX.XXXX..XXXX.X..X.XXXX.X........X.X.XXXX?XXXX.XX.....XXX.XXX...X....
> XX.X.X......XX.X..XXX...XXXXX..X.XX.XX..XX....X...XXXXXX.XXXX...X..XXX..
> .X.X..X.XXXXX..XX.X...XXX....XX.X.XX.X....X.XX..X....XXXXXX.X.X...X..X.X
> ....X.XXX..X.X...XX...X..XX.X..XX.X.......XXX.X..X.X.X.X.XX.....X..XX...
> X.X..XX..X.XXX..XX.XXX.X...X....XX.X......X...X.XXX.X.XX..XXX..X.....XX.
> .X..X.XXXXX...X.X.X.X.X..XXXXX...X.XX..X.....XXX.XX.XXX...XXXXX..XXX.XXX
> ...X.X....XX..XXXX.XXXXXX.XX..X.XX.X...XXXXXXXXXXXX..X.......XXX.X.X..XX
> XXX..XXX...XX.XXX.X..X......XXX.X....X.X.X.....X...XX.X..XX..X..X.X.X...
> ..X....XXX.X......X..XX.X..X....X.XX.X...X.X.X...X.XXXX.X.X.X..XX...X..X
> .X..X..XX.X.....XX.X.XX.XXXX......X.X.X..X..X....X..X..X.X..X..XX.XX..X.
> XXXX...X...X.X.XXXX....X.X.XXXX.XX.XX...XX.XX......X.XXX.XX..X..X.....XX
> X.X.XXX.X....XXXX.X.XXX..XXX.....X.X.XXX.XX...X..XXXXXXXX.X.X.X.XX.XX..X
> XX..X..XX........XX..X.XX...XX.XXX....X.XX..X....X..XXX...XXXX
> 
> 73,
> 
> Stewart KK7KA