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
>
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