[Elecraft] [K3] what audio passband should I expect in TX DATA/DATA A mode?

[Jim Brown]

Hi Guys,

As an active WSJT-mode user, I'll attempt to clarify this set of issues. 
For a more complete answer, download the WSJT 10 and WSJT-X pdf documents.

WSJT 10 and WSJT-X are designed for the rig to be set for the full USB 
bandwidth of an average radio. Each mode has an agreed upon slice of 
each of the HF and VHF bands. For JT65, WSJT-X includes as defaults the 
dial frequencies for those agreed upon slices, which are from about 400 
Hz to about 3 kHz above the dial frequency.  The 400 Hz and 3 kHz points 
are the result of the IF filters, and can be varied a bit from one radio 
to another. On 20M, for example, a dial frequency of 14,076 kHz puts 
JT65 between 14,076.4 and 14,079.

The slice for JT9 is 2 kHz higher, with a dial frequency 2 kHz higher. 
This puts their operating slice between 14,078.4 and about 14,081 kHz. 
Note the overlap, which is intentional. WSJT-X can be set to decode BOTH 
JT65 and JT9. If, for example, you call CQ with a dial frequency of 
14,076 and 2.2 kHz audio, it will be within the passband of other radios 
tuned to 14076, and they can decode you. Go higher than 3 kHz audio and 
you're taking your chances. :)

This one for Matt: Joe Taylor, K1JT, the inventor of the WSJT modes, 
strongly recommends that the rig be set for full USB bandwidth, and that 
we allow his software to do the filtering to separate signals from each 
other. We talked about this at Pacificon several years ago. The reason 
is simple -- filters creates phase shift, and phase shift is the enemy 
of good decoding.

Another thing -- WSJT-X is undergoing extensive development, and will 
eventually include most WSJT modes, not just JT65 and JT9. The latest 
versions of WSJT-X have added a feature that, if the rig supports it, 
will set the rig for split mode with different audio tones on the TX 
than the RX but setting the split so that they come out on the right 
frequency!

Again, RTFM -- this time the WSJT-X manual.

73, Jim K9YC

On Sun,8/23/2015 12:51 PM, Pierfrancesco Caci wrote:
>>>>>> "Matt" == Matt Zilmer <mzilmer at roadrunner.com> writes:
>
>      Matt> Hi Pf,
>      Matt> Most tone modes operate at an offset from carrier frequency, so that
>      Matt> the audio frequencies of interest are more or less cenetered in the
>      Matt> filter passband.  I believe the JTx modes are already in the 1200 to
>      Matt> 1500 Hz range so no offset is required.
>
> Hi Matt,
> actually, I'm seeing JT9 stations transmitting at 3400 Hz, and who knows
> if there are some even above that. JT65+JT9 uses quite a wide receive
> window.
>
>
>      Matt> The crystal filter being used only restricts the bandwidth of the RX
>      Matt> chain (1st IF).  The DSP imposes its own audio filtering on the
>      Matt> baseband, and that's what you're seeing as rolloff below ~300 and
>      Matt> above ~3500 Hz.
>
> Yes, and that was what I wanted to know. I've read in this mailing list
> that the DSP limits the audio at 4 kHz. I'm seeing it roll off at little
> above 3400. The low end rolls off at around 300, so I'm getting an audio
> passband of ~3100 Hz. I wonder if this is normal, or if there's
> something else I can tweak in the settings.
>
>
> Pf
>