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

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Pierfrancesco Caci

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

Hello,
I'm dabbling with wsjtx, and I see that my rx audio has some definite roll
off at <300 Hz and >3500 Hz. Selected filter is the 12 kHz one, and
width is set to 4 kHz. Audio soundcard is the Numark studio-io, but I
also saw this with an el-cheapo adapter.
Also, I see the same roll-off in fldigi, so the final application should
not matter.
Am I doing something wrong? What should be the audio passband available
at line out connector?

Thanks

Pf

--
Pierfrancesco Caci, ik5pvx
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Matt Zilmer-3

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

Hi Pf,

Most tone modes operate at an offset from carrier frequency, so that
the audio frequencies of interest are more or less cenetered in the
filter passband. I believe the JTx modes are already in the 1200 to
1500 Hz range so no offset is required.

The crystal filter being used only restricts the bandwidth of the RX
chain (1st IF). The DSP imposes its own audio filtering on the
baseband, and that's what you're seeing as rolloff below ~300 and
above ~3500 Hz.

73,
matt
W6NIA

On Sun, 23 Aug 2015 19:03:21 +0200, you wrote:

>
>Hello,
>I'm dabbling with wsjtx, and I see that my rx audio has some definite roll
>off at <300 Hz and >3500 Hz. Selected filter is the 12 kHz one, and
>width is set to 4 kHz. Audio soundcard is the Numark studio-io, but I
>also saw this with an el-cheapo adapter.
>Also, I see the same roll-off in fldigi, so the final application should
>not matter.
>Am I doing something wrong? What should be the audio passband available
>at line out connector?
>
>Thanks
>
>Pf

Matt Zilmer, W6NIA
--
"Always store beer in a dark place." -R. Heinlein

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Pierfrancesco Caci

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

>>>>> "Matt" == Matt Zilmer <[hidden email]> 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

--
Pierfrancesco Caci, ik5pvx
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Joe Subich, W4TV-4

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

> 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.

It depends on your "roofing" filter ... If you have an AM (6 KHz) or
FM (13 KHz) filter, you will see 300 Hz to 4200 Hz with FC=2.20 and
BW=4.00 (at -3dB). If you only have a 2.8 KHz filter, bandwidth
will be around 2800 Hz (900 - 3700 with FC=2.20 and BW=4.00 or 400 -
3200 with FC=1.60 and BW=4.00).

If you see roll-off at 3400 Hz you either have a narrow roofing filter
or the DSP center frequency (FC) is set too low.

73,

... Joe, W4TV

On 8/23/2015 3:51 PM, Pierfrancesco Caci wrote:

>>>>>> "Matt" == Matt Zilmer <[hidden email]> 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
>

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Pierfrancesco Caci

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

>>>>> "Joe" == Joe Subich, W4TV <[hidden email]> writes:

Joe> It depends on your "roofing" filter ... If you have an AM (6 KHz) or
Joe> FM (13 KHz) filter, you will see 300 Hz to 4200 Hz with FC=2.20 and
Joe> BW=4.00 (at -3dB). If you only have a 2.8 KHz filter, bandwidth
Joe> will be around 2800 Hz (900 - 3700 with FC=2.20 and BW=4.00 or 400 -
Joe> 3200 with FC=1.60 and BW=4.00).

Joe> If you see roll-off at 3400 Hz you either have a narrow roofing filter
Joe> or the DSP center frequency (FC) is set too low.

Joe> 73,

Thanks Joe,
this is exactly what I needed to know. I'm using the FM filter, and
moving the passband up (by using SHIFT until FC=2.2), I can get the full
4 kHz, from slightly less than 300 Hz to slightly more than 4100.
I've saved this as NORM2 for data mode.

Pf

--
Pierfrancesco Caci, ik5pvx
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Jim Brown-10

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

In reply to this post by Pierfrancesco Caci

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 <[hidden email]> 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
>