[RTTY] Spectrum of RTTY signal
Marijan Miletic, S56A
artinian@siol.net
Sun, 2 Sep 2001 20:46:05 -0000
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Sharp 270 Hz filter seems to be the optimum, if we can only get phase
continious AFSK within 22 msec data frame.
I hope this is done within modern radios with digital techniques and two
separate division rates for mark and space tones from the common baud rate
frequency source.
I survived 5 days without Internet while enjoying SSB FD contest.
73 de Mario, S56A, N1YU
----- Original Message -----
From: Kok Chen
To: rtty@contesting.com
Sent: Wednesday, August 29, 2001 3:55 PM
Subject: [RTTY] Spectrum of RTTY signal
Hi Folks,
I have the spectrum of an RTTY signal posted at
http://homepage.mac.com/chen/.Public/RTTY/fskspec.pdf
This is an Acrobat (pdf) file.
A 45.45 baud, 170 Hz shift signal with 32 uniformly distributed
random bits is generated, and a Hamming windowed FFT is taken.
The FSK is generated in a phase continuous manner (the carrier
phase angle at the beginning of a bit is set to the phase angle
at the end of the previous bit).
[i.e., the FSK time waveform is continuous, although the derivative
of the waveform is not necessarily continuous]
There is no shaping of the data bits, data transitions are
instantaneous.
4,000 of these spectra are computed and averaged, equivalent
to something like 45 minutes of real time signals (but only took
a couple of seconds of computation on a current portable computer).
The vertical axis of the plot is on a square root amplitude scale.
This is so that the sidebands show up well. A linear power scale
won't show them at all, as you can imagine, and with a linear
scale, the details are not clear. A traditional log plot would
have overwhelming sidebands. So, I settled for square root
amplitude plot.
The tick marks on the horizontal scale are at 10 Hz intervals.
The vertical dotted lines indicate the 250 Hz bandwidth limits.
73
Chen, AA6TY
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
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<DIV><FONT face=3DArial size=3D2>Sharp 270 Hz filter seems to be the =
optimum, if we=20
can only get phase continious AFSK within 22 msec data =
frame.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I hope this is done within modern =
radios with=20
digital techniques and two separate division rates for mark and space =
tones from=20
the common baud rate frequency source.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I survived 5 days without Internet =
while enjoying=20
SSB FD contest.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>73 de Mario, S56A, N1YU</FONT></DIV>
<BLOCKQUOTE=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dkchen@apple.com href=3D"mailto:kchen@apple.com">Kok =
Chen</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Drtty@contesting.com=20
href=3D"mailto:rtty@contesting.com">rtty@contesting.com</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, August 29, =
2001 3:55=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [RTTY] Spectrum of =
RTTY=20
signal</DIV>
<DIV><BR></DIV>Hi Folks,<BR><BR>I have the spectrum of an RTTY signal =
posted=20
at<BR><BR><A=20
=
href=3D"http://homepage.mac.com/chen/.Public/RTTY/fskspec.pdf">http://hom=
epage.mac.com/chen/.Public/RTTY/fskspec.pdf</A><BR><BR>This=20
is an Acrobat (pdf) file.<BR><BR>A 45.45 baud, 170 Hz shift signal =
with 32=20
uniformly distributed<BR>random bits is generated, and a Hamming =
windowed FFT=20
is taken.<BR><BR>The FSK is generated in a phase continuous manner =
(the=20
carrier<BR>phase angle at the beginning of a bit is set to the phase=20
angle<BR>at the end of the previous bit).<BR><BR>[i.e., the FSK time =
waveform=20
is continuous, although the derivative<BR>of the waveform is not =
necessarily=20
continuous]<BR><BR>There is no shaping of the data bits, data =
transitions=20
are<BR>instantaneous. <BR><BR>4,000 of these spectra are computed and=20
averaged, equivalent<BR>to something like 45 minutes of real time =
signals (but=20
only took<BR>a couple of seconds of computation on a current portable=20
computer).<BR><BR>The vertical axis of the plot is on a square root =
amplitude=20
scale.<BR>This is so that the sidebands show up well. A linear =
power=20
scale<BR>won't show them at all, as you can imagine, and with a=20
linear<BR>scale, the details are not clear. A traditional log =
plot=20
would<BR>have overwhelming sidebands. So, I settled for square=20
root<BR>amplitude plot.<BR><BR>The tick marks on the horizontal scale =
are at=20
10 Hz intervals.<BR><BR>The vertical dotted lines indicate the 250 Hz=20
bandwidth limits.<BR><BR><BR>73<BR><BR>Chen,=20
AA6TY<BR><BR>_______________________________________________<BR>RTTY =
mailing=20
list<BR><A =
href=3D"mailto:RTTY@contesting.com">RTTY@contesting.com</A><BR><A=20
=
href=3D"http://lists.contesting.com/mailman/listinfo/rtty">http://lists.c=
ontesting.com/mailman/listinfo/rtty</A></BLOCKQUOTE></BODY></HTML>
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