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

[Joe Subich, W4TV]

> 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 <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
>