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Re: [Discuss-gnuradio] Comb Filter

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] Comb Filter
Date: Thu, 06 Jan 2005 01:16:23 +0100
User-agent: Mozilla Thunderbird 0.9 (X11/20041124)

Prateek Dayal wrote:
Thanks Martin,

Going by this approach, I feel following simplifications will again work

1. No need to supress the audio carrier

2. No need to shape the VSB modulated signal. (to compensate for the
frequency information that is there in both + and - bands around 0 )

I mean there should be atleast some display, but the point 2 above may
cause more problem like some kind of saturation ....

If you use as first component a freq_xlating_fir_filter with a bandwith of 1 MHz in stead of 5 MHz then you supress most of the audio carrier and you have less vestigal sideband problems and supress most of the audio carrier.
(one sideband is 1 Mhz, the other sideband is more then 5 Mhz, if you use only 
the lower 1 Mhz you have a normal symmetrical AM signal)
You miss the fine details and the ability to extract color information this way 

The decimation factor to use in the freq_xlating_fir_filter depends on the IF 
frequency used.
If you use the normal IF of 36 Mhz you can go up to around 18 to still have 
1Mhz of signal bandwith in the output signal.
If you use a Rf frontend with a lower IF then you need to use a lower 
decimation factor.


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