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John:
Be aware that, if you cascade two 250 Hz filters, you get less than 250 Hz. For
example, if both responses were identical, the -3dB points become -6 dB points.
Also note that the clever overlay showed one 250 Hz filter.
Garry
John Lockhart wrote:
> Thanks Bruce and Chen,
>
> It looks like the 250 Hz filters should work fine, which has been my
> experience with cascaded Kenwood, ICOM and Yaesu factory filters.
> (non-DSP!)
>
> 73,
>
> John W0DC
> -----Original Message-----
> From: Bruce Lifter, WT4I rr <wt4i@cfl.rr.com>
> To: rtty@contesting.com <rtty@contesting.com>
To: <rtty@contesting.com>
> Date: Wednesday, August 29, 2001 23:18
> Subject: RE: [RTTY] Spectrum of RTTY signal
>
> >I did my best to take Chen's figure and overlay one of INRAD's
> >250Hz filters. (I did a screen capture dumped it into paint and then played
> >"connect the dots" with the data extrapolated from the INRAD graph.)
> >
> >Here is the link to the filter:
> >http://www.qth.com/inrad/graphs/186.gif
> >
> >Here is the link to Chen's figure overlayed with the filter:
> >http://www.wt4i.com/Demo/250HzFilter2.gif
> >
> >73, Bruce
> >
> >
> >
> >> -----Original Message-----
> >> From: rtty-admin@contesting.com [mailto:rtty-admin@contesting.com]On
> >> Behalf Of Kok Chen
> >> Sent: Wednesday, August 29, 2001 11:56 AM
> >> To: rtty@contesting.com
> >> 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
>
> _______________________________________________
> RTTY mailing list
> RTTY@contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
--
160 meters-not a band but an obsession
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John:
<p>Be aware that, if you cascade two 250 Hz filters, you get less than
250 Hz. For example, if both responses were identical, the -3dB points
become -6 dB points. Also note that the clever overlay showed <i>one</i>
250 Hz filter.
<p>Garry
<p>John Lockhart wrote:
<blockquote TYPE=CITE>Thanks Bruce and Chen,
<p>It looks like the 250 Hz filters should work fine, which has been my
<br>experience with cascaded Kenwood, ICOM and Yaesu factory filters.
<br>(non-DSP!)
<p>73,
<p>John W0DC
<br>-----Original Message-----
<br>From: Bruce Lifter, WT4I rr <wt4i@cfl.rr.com>
<br>To: rtty@contesting.com <rtty@contesting.com>
To: <rtty@contesting.com>
<br>Date: Wednesday, August 29, 2001 23:18
<br>Subject: RE: [RTTY] Spectrum of RTTY signal
<p>>I did my best to take Chen's figure and overlay one of INRAD's
<br>>250Hz filters. (I did a screen capture dumped it into paint and then
played
<br>>"connect the dots" with the data extrapolated from the INRAD graph.)
<br>>
<br>>Here is the link to the filter:
<br>><a
href="http://www.qth.com/inrad/graphs/186.gif";>http://www.qth.com/inrad/graphs/186.gif</a>
<br>>
<br>>Here is the link to Chen's figure overlayed with the filter:
<br>><a
href="http://www.wt4i.com/Demo/250HzFilter2.gif";>http://www.wt4i.com/Demo/250HzFilter2.gif</a>
<br>>
<br>>73, Bruce
<br>>
<br>>
<br>>
<br>>> -----Original Message-----
<br>>> From: rtty-admin@contesting.com [<a
href="mailto:rtty-admin@contesting.com";>mailto:rtty-admin@contesting.com</a>]On
<br>>> Behalf Of Kok Chen
<br>>> Sent: Wednesday, August 29, 2001 11:56 AM
<br>>> To: rtty@contesting.com
<br>>> Subject: [RTTY] Spectrum of RTTY signal
<br>>>
<br>>>
<br>>> Hi Folks,
<br>>>
<br>>> I have the spectrum of an RTTY signal posted at
<br>>>
<br>>> <a
href="http://homepage.mac.com/chen/.Public/RTTY/fskspec.pdf";>http://homepage.mac.com/chen/.Public/RTTY/fskspec.pdf</a>
<br>>>
<br>>> This is an Acrobat (pdf) file.
<br>>>
<br>>> A 45.45 baud, 170 Hz shift signal with 32 uniformly distributed
<br>>> random bits is generated, and a Hamming windowed FFT is taken.
<br>>>
<br>>> The FSK is generated in a phase continuous manner (the carrier
<br>>> phase angle at the beginning of a bit is set to the phase angle
<br>>> at the end of the previous bit).
<br>>>
<br>>> [i.e., the FSK time waveform is continuous, although the derivative
<br>>> of the waveform is not necessarily continuous]
<br>>>
<br>>> There is no shaping of the data bits, data transitions are
<br>>> instantaneous.
<br>>>
<br>>> 4,000 of these spectra are computed and averaged, equivalent
<br>>> to something like 45 minutes of real time signals (but only took
<br>>> a couple of seconds of computation on a current portable computer).
<br>>>
<br>>> The vertical axis of the plot is on a square root amplitude scale.
<br>>> This is so that the sidebands show up well. A linear power
scale
<br>>> won't show them at all, as you can imagine, and with a linear
<br>>> scale, the details are not clear. A traditional log plot would
<br>>> have overwhelming sidebands. So, I settled for square root
<br>>> amplitude plot.
<br>>>
<br>>> The tick marks on the horizontal scale are at 10 Hz intervals.
<br>>>
<br>>> The vertical dotted lines indicate the 250 Hz bandwidth limits.
<br>>>
<br>>>
<br>>> 73
<br>>>
<br>>> Chen, AA6TY
<br>>
<br>>_______________________________________________
<br>>RTTY mailing list
<br>>RTTY@contesting.com
<br>><a
href="http://lists.contesting.com/mailman/listinfo/rtty";>http://lists.contesting.com/mailman/listinfo/rtty</a>
<p>_______________________________________________
<br>RTTY mailing list
<br>RTTY@contesting.com
<br><a
href="http://lists.contesting.com/mailman/listinfo/rtty";>http://lists.contesting.com/mailman/listinfo/rtty</a></blockquote>
<p>--
<br>160 meters-not a band but an obsession
<br> </html>
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![http://www.qth.com/inrad/graphs/186.gif"](http://www.qth.com/inrad/graphs/186.gif"){kind=link}
![http://www.wt4i.com/Demo/250HzFilter2.gif"](http://www.wt4i.com/Demo/250HzFilter2.gif"){kind=link}