[RTTY] Crystal filter width preferences for RTTY contesting

[WS7I]

You're right most 455 Khz filters are like this one and have a 1.8 shape factor.  
http://www.inrad.net/product.php?productid=157&cat=105

That of course works perfectly fine in the final IF of a Yaesu FT-1000XX transceiver.

Most aren't 8 Mhz IF filters.  

Actually 45.45 baud is 270 Hz wide at 60 WPM.


--
ws7i at ewarg.org



---------- Original Message ----------------------------------
From: "Joe Subich, W4TV" <lists at subich.com>
Reply-To: lists at subich.com
Date:  Tue, 25 Aug 2009 17:33:56 -0400

>
>250 Hz is really too narrow unless one has a high s/n and 
>the interference is from a strong adjacent signal that is 
>activating the AGC. 
>
>As a first approximation the RTTY signal can be thought of 
>as a 22.7 Hz square wave ... to reproduce that square wave 
>with minimal distortion requires at least the fundamental, 
>3rd and 5th harmonics (22.7*5 or approximately 115 Hz) for 
>285 Hz.  Adding the 7th harmonic of the bit clock one gets 
>22.7*7 + 170 or approximately 330 Hz.   
>
>Most amateur filters are specified at -6 dB corner frequencies 
>where we really need to be flat or down no more than 1 dB for 
>the 285 Hz bandwidth so the argument would be for a -6dB width 
>of roughly 300 to 325 Hz.  Again, much of this will depend on 
>the filter behavior at the knee - how sharply it transitions 
>from passband to skirt - and the steepness of the filter 
>skirts. 
>
>Many have had luck in using "250 Hz" filters with shape 
>factors in the 1.8 - 2.0 range but these 250 Hz filters 
>generally measure significantly wider than nominal (see: 
>http://www.inrad.net/product.php?productid=214 or 
>http://www.elecraft.com/K3/K3_8_pole_plots.htm) so the 
>"250 Hz" reports should be taken with a grain of salt. 
>
>73, 
>
>   ... Joe, W4TV 
> 
>
>
>> -----Original Message-----
>> From: rtty-bounces at contesting.com 
>> [mailto:rtty-bounces at contesting.com] On Behalf Of Jens Petersen
>> Sent: Tuesday, August 25, 2009 4:21 PM
>> To: RTTY contesting
>> Subject: Re: [RTTY] Crystal filter width preferences for RTTY 
>> contesting
>> 
>> 
>> On Tue, 25 Aug 2009 12:23:26 -0500, you wrote:
>> 
>> 
>> >Q1. If you only were to get 1 filter, what width would it be?
>> 
>> 250Hz 
>> 
>> I use 250Hz roofing filter on my K3 and it works super.
>> 
>> -- 
>> OV1A Jens
>> 
>>  Good decisions come from experience. Experience comes from 
>> making bad ones _______________________________________________
>> RTTY mailing list
>> RTTY at contesting.com http://lists.contesting.com/mailman/listinfo/rtty
>
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