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@ewarg.org
---------- Original Message ----------------------------------
From: "Joe Subich, W4TV" <lists@subich.com>
Reply-To: lists@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@contesting.com
>> [mailto:rtty-bounces@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@contesting.com http://lists.contesting.com/mailman/listinfo/rtty
>
>_______________________________________________
>RTTY mailing list
>RTTY@contesting.com
>http://lists.contesting.com/mailman/listinfo/rtty
>[This E-mail scanned for viruses by ClamAV]
>
>
[This E-mail scanned for viruses by ClamAV]
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|