[Elecraft] K3 question, PSK and AM filter option from G4HUE

[Joe Subich, W4TV]

> My question is that I would like to be able to simultaneously decode
> more than 2.8KHz (HRD is limited to 3.9KHz) of the ham band at once.
> I have thought about fitting the 6KHz AM filter (there not being a
> 4KHz filter available). One part of me says that would work just
> fine and the other part of me says “don’t be silly” there will be
> 3KHz of LSB and 3KHz of USB and it will all go horribly wrong. I
> guess someone out there has tried and can tell me which of my
> premonitions is correct??

I don't think your premonitions are correct abut things going terribly
wrong.  However, my feeling is "why bother?"  The K3 transmit audio in
DATA A rolls off significantly below roughly 300 Hz and above 3000 Hz
(maybe 200/2900 Hz it's been a while since I tested it) thus any RX
bandwidth above 3 KHz would be "receive only".

The 2800 Hz/8 pole filter is about 2900 Hz or slightly wider at the
-6DB points in any case and will have significant response on the
filter skirts so you will certainly find response to 3.9 KHz if you
set the DSP to allow it (even though the response may be down a fair
bit).

> As a suplementary will this be limited by any audio filtering in the
> K3, I seem to recall reading that the K3's audio is limited to a
> bandwidth of 4.2KHz but of course I can find the reference now!!

The DSP is limited to approximately 4.2 KHz output.  The DAC which
feeds the headphone and speaker outputs is followed by a lowpass
filter at 4.2 KHz to remove clock leakage and other artifacts.
Although the DAC which feeds the Line Out does not also include
a LPF, the DSP programming is the same including the 4.2 KHz
cutoff.

73,

    ... Joe, W4TV


On 12/24/2012 4:19 PM, ANDY NEHAN wrote:
> Happy Xmas guys and a healthy and prosperous New Year to all.
>
> I am
> a recent convert to the K3 with model 6990.
>
> I am primarily a data mode operator (PSK31 etc. etc.) and my
> K3 has the 2.8KHz and 250Hz 8 pole filters fitted and let me say its doing a
> very fine job too. I use HRD version 5 which appears to force the sound card to
> sample at 8KHz (in my case it’s the Signalink USB). My question is that I would
> like to be able to simultaneously decode more than 2.8KHz (HRD is limited to 3.9KHz) of the ham band at once.
> I have thought about fitting the 6KHz AM filter (there not being a 4KHz filter
> available). One part of me says that would work just fine and the other part of
> me says “don’t be silly” there will be 3KHz of LSB and 3KHz of USB and it will
> all go horribly wrong. I guess someone out there has tried and can tell me
> which of my premonitions is correct?? As a suplementary will this be limited by any audio filtering in the K3, I seem to recall reading that the K3's audio is limited to a bandwidth of 4.2KHz but of course I can find the reference now!!
>
>
> Thanks in advance guys.
>
> Andy
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