[Elecraft] RTTY Filter for K3

[Frank Lammel]

Hi Axel,

full ack with Joe. I use the 400 Hz 8 Pole with a DSP of about 300-350 
in dual tone. Perfect!

73!
Frank, DD7ZT



Joe Subich, W4TV schrieb:

> After making extensive tests and plotting the selectivity curves 
> of the 200 Hz filter in my K3, I'm convinced that it is too 
> narrow for reliable weak signal RTTY operation, particularly in 
> conjunction with the dual-tone filter.  
> 
> The measured -6dB bandwidth of the 200 Hz crystal filter was 
> 209 Hz and the composite bandwidth of the 200 Hz crystal filter, 
> 200 Hz DSP and dual tone fitter was less than 170 Hz.  A standard 
> 170 Hz shift 45.45 baud RTTY signal needs at least 235 Hz 
> (170 + 3*22.7) and the dual tone filter represents a 220 Hz (two 
> 50 Hz filters with center frequencies separated by 170 Hz). 
> 
> After extended discussion with a well know RTTY op and K3 beta 
> tester, I believe the combination of a 300 Hz 5-pole crystal filter,
> 300 Hz DSP and the dual tone filter will have a composite -6 dB 
> bandwidth of about 250 Hz - about optimum for narrow RTTY.  The 
> currently available, "250," "400" or 500 Hz filters in combination 
> with a 300 Hz DPS bandwidth and dual tone filter are very close to 
> optimum.  
> 
> 73, 
> 
>    ... Joe, W4TV 
>      
> 
> 

>>
>> Hi K3-folks,
>>
>> What would be the best RTTY roofing filter for the K3? Is the 
>> 400Hz 8-pole 
>> filter too small and the 500Hz 5-pole filter the better choice?
>>
>> Thanks in advance for your answers.
>>
>> 73 de
>>
>> Axel, DL3ZH
>>