[RTTY] MMTTY Tx Tab settings

[Joe Subich, W4TV]

If your computer is not CPU limited (e.g. an old < 2 GHz Pentium),
I would use 512 taps and 400 Hz (type in 400).  With an older CPU,
you can probably get away with 96 or 128 taps but not have quite as
"clean" a signal (even the default 48 tap setting has some benefit).

Note - it is still important to connect AFSK audio to the rig's "Line"
input (typically a DATA, ACC or PKT jack - even a phone patch input) to
prevent over driving the audio stages as well as as well as properly
bonding the computer, interface and rig to avoid introducing hum and
RF feedback ("common mode" RFI).  Also disconnect the microphone and
keep power output below about 80 watts (with rigs using "12V" final
transistors) to minimize IMD in the final amplifier.

A good article on the issues of "filtered AFSK" was written by K0SM
several years ago:
     http://www.frontiernet.net/~aflowers/k3rtty/k3rtty.html

73,

    ... Joe, W4TV


On 4/26/2017 10:35 AM, Ktfrog007 at aol.com wrote:
> Hi Joe,
>
> What do you consider the best/optimal settings for Tap and Freg?  I do
> AFSK.
>
> 73,
> Ken, AB1J
>
>
> In a message dated 2017-04-26 1:31:04 P.M. Coordinated Universal Tim,
> lists at subich.com writes:
>
>
>>  What do each of these do and what are the optimum settings?
>> Tx BPF  check  box                [default  = Selected?]
>
> Enables a bandpass filter in the AFSK  output.  The bandpass filter
> removes distortion products and  harmonics.
>
>> Tx LPF check  box         [default  = not Selected]
>
> Enables a  lowpass filter in the AFSK output.  The lowpass filter
> removes  harmonics, it does not impact distortion or  switching
> transients.
>
> Note: these filters only act on the audio  generated by the sound
> card.  They do not remove distortion/harmonics  generated by
> running the sound card at maximum output level (clipping in  the
> analog output) or over driving the input of the transceiver. Nor
> do  they remove hum caused by improper grounding/bonding of the
> computer  soundcard, interface, and transceiver.
>
>> Tap (range 24-512)   [default = 48]
>
> Controls the steepness  of the filter skirts.  Full details is an
> in depth topic on the  mathematics of digital signal processing.
>
>> Freq in hz (range  40-600)    [default = 100]
>
> Controls the width of the bandpass  filter.  Note: with high tap
> numbers (steep sided filters) the  bandwidth should be *greater than*
> 400Hz to prevent loss of "sharpness" in  the mark/space transitions.
>
> 73,
>
> ... Joe,  W4TV
>
>
> On 4/26/2017 9:00 AM, Kermit (aka Ken) via RTTY wrote:
>>  I'd like some info on setting parameters in the TxBPF/TxLPF box in   the
>> MMTTY TX Tab section .
>>
>> I can't find good  documentation in the MMTTY help file.  There has  been
>> some  discussion here recently.
>>
>> The parameters and their apparent  default settings (from  most Profiles)
>> are:
>>
>> Tx  BPF check  box                [default  = Selected?]
>> Tap (range 24-512)       [default = 48]
>> Tx LPF check  box     [default  = not  Selected]
>> Freq in hz (range 40-600)    [default =  100]
>>
>> What do each of these do and what are the optimum  settings?
>>
>> Thanks & 73,
>> Ken,  AB1J
>>
>>
>>
>> In a message dated 2017-04-25 2:18:13  P.M. Coordinated Universal Tim,
>> lists at subich.com  writes:
>>
>> On  4/25/2017 10:04 AM, Ed Muns  wrote:
>>>  Set MMTTY taps to 512  too.
>>
>> AND  *check* TxBPF (TX tab) it is not checked by default.
>> TxBPF  is  not needed for FSK and increases the processor
>> load (for  marginal  systems) on AFSK.
>>
>> You will also want to set  Freq (bandwidth) to 600 Hz  (or
>> enter 400 Hz manually).  300  Hz is too narrow with  512
>> taps.
>>
>>  73,
>>
>> ... Joe, W4TV
>>
>>
>> On  4/25/2017  10:04 AM, Ed Muns wrote:
>>> AFSK on the K3/K3S is fine with low   tones if the radio AFSK TX filter
>>> is enabled. Set MMTTY taps to  512  too. Make sure to set the same
>>> audio  tone pair in  both the radio  and MMTTY.
>>>
>>> 73,
>>>  Ed  W0YK
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