Re: [RTTY] Filters

[Kok Chen <chen@mac.com>]

On Mar 27, 2004, at 7:12 AM, Bill Turner wrote:
> But you're right about shape being important too.  That affects how far
> off you would tune and how quickly the interfering signal drops off.

When two signals are intertwined, a double humped filter would help 
since 45 baud modulation hardly uses any of the bandwidth at the center 
of a 170 Hz shift FSK signal.

If there are going to two RTTY signals cohabiting the same part of the 
spectrum, a 85 Hz Mark separation between the two interfering signals 
is probably ideal.  It then gets _worse_ as the separation increases, 
until the Mark tones are 170 Hz from one another.  From there it gets 
better as the separation increases, until you get to where they no 
longer overlap.

The Timewave 599zx has a filter that is double humped, but the DSP 
filter on the FT-1000MP does not, in spite of Yaesu ads touting it as a 
"digital mode receiver" or something like that.  Perhaps they think OOK 
is a "digital mode" :-).

Any of you who wants to steal my frequency should place yourself 
precisely 85 Hz away, HI HI.

Hmmm (evil grin)... during a pile up, placing yourself 85 Hz above the 
pile is perhaps a good thing?  You are still in the DX's receive 
passband, plus you are moderately orthogonal to the rest of the 
unwashed masses... as long as there is no second smart aleck who had 
placed himself 85 Hz _below_ the pile!!

73
Chen, W7AY

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