[CQ-Contest] RTTY contesting; filters

[Jeff Blaine]

Like Ed, I generally run a wider roofing filter and rely on the decoder 
software to do the close in filtering.  It takes a while to wrap your 
head around the idea that what we hear as humans is not really the way 
the decoder hears the world.

Using 200 Hz on a set of 170 Hz spaced tones will result in chopping off 
the power in the sidebands which hampers the decoder performance.  And 
depending on the way the rig filtering is implemented, probably 
introducing more problems than it solves.

Modern decoders are exceptionally capable beasties - far more than a set 
of human ears.  For best results, I want the decoder to do the heavy 
lifting and keep the rig - and your human impulses - out of the way.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 2/17/21 7:56 PM, WW3S wrote:
> I was cranked down to 200 hz and would have gone tighter if I could.....btw, congrats John on what appears to be a first place finish, I just couldn’t get much going with low power this weekend....
>
> Sent from my iPad
>
>> On Feb 17, 2021, at 8:37 PM, john at kk9a.com wrote:
>>
>> I am sure that is true on a quiet band. I wish that I could find a 600hz
>> opening anywhere on 20m in last weekend's contest. Any QRM in my passband
>> makes decoding very difficult.
>>
>> John KK9A
>>
>>
>>
>> Ed Muns w0yk wrote:
>>
>> An IF bandwidth of 600 Hz is ideal with our modern software decoders.
>> (Narrower bandwidth introduces phase shift that degrades copy error rate.)
>> Older radios often don't allow narrow filtering in SSB mode.  Yes, you want
>> to shift such that the bandpass is centered on whatever tone pair you use.
>>
>>
>>
>> I do like lower tones and typically use 915/1085 which is less fatiguing
>> over long periods.  OTOH, their TX audio harmonic is still within the normal
>> 2 kHz bandwidth for SSB transmitters when transmitting AFSK.  Not a problem
>> for those of us using FSK.
>>
>>
>>
>> 73,
>>
>> Ed W0YK
>>
>> _______________________________________________
>> CQ-Contest mailing list
>> CQ-Contest at contesting.com
>> http://lists.contesting.com/mailman/listinfo/cq-contest
> _______________________________________________
> CQ-Contest mailing list
> CQ-Contest at contesting.com
> http://lists.contesting.com/mailman/listinfo/cq-contest