[Elecraft] K3 - AFSK anamoly? No replies, try again

[Mike Murray]

Joe, et.al.,

I finally got back to the shack to check the setup.  It looks like I was
actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
dual PB DSP filter.  I also checked the filter offsets which were all at
0.0 (all 8 pole) and I was using AFSK A mode.  Is the effect I'm seeing due
to use of the 1.8 filter or do I have more research to do?

Thanks for everyone's input and patience - seems like the learning curve is
getting worse with age.

Mike - W0AG

On Wed, Jan 6, 2016 at 6:14 PM, Joe Subich, W4TV <lists at subich.com> wrote:

>
> Since I'm new to RTTY, I probably didn't describe my question in
>> correct terminology - I mainly only operate CW. I'll try again....
>>
>
> And I'll ask my questions again ... what *ROOFING FILTER* and what DSP
> bandwidth are you using?
>
> As Eric said in reply to your posting, this sounds like the offset is
> incorrect on the roofing filter and allowing you to tune "past" zero
> beat.  This is particularly true if you are using the SSB filter and
> a wide DSP setting instead of the more typical CW filter (500 Hz)
> centered on the mark/space tones (915/1085 Hz in your case).
>
> Note: RTTY is typically lower sideband with MARK being the lower audio
> tone and space being the higher audio tone because of the "reversal"
> that occurs in the audio to RF translation.  In the K3 AFSK A is LSB
> but DATA A is USB ... if you are using them interchangeably that may
> also be causing you some confusion.
>
> 73,
>
>   ... Joe, W4TV
>
>
> On 1/6/2016 6:47 PM, Mike Murray wrote:
>
>> Bob, Joe, Bill & Mike,
>>
>> Since I'm new to RTTY, I probably didn't describe my question in correct
>> terminology - I mainly only operate CW.  I'll try again....
>>
>> I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY
>> dual-PB
>> filter.  To illustrate what I'm hearing/seeing, imagine tuning down from
>> 14.090 until you hear and can decode an RTTY signal.  Then continue tuning
>> down 915 Hz (to what I probably erroneously referred to as zero beat) and
>> then down another 915 Hz, I can now hear the same signal but inverted
>> (slightly weaker, but definitely there).  It is not decodeable, but it is
>> definitely there.  I assumed (yeah, I know) that the opposite sideband
>> should be suppresed, but I think that's what I'm hearing.  Any advice will
>> be appreciated.
>>
>> Mike - W0AG
>>
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