[RTTY] K3 reduced-bandwidth RTTY analysis

[Joe Subich, W4TV]

 > I have tried to download theirs FW release notes, but no way by now.
 > The .rtf that I could get here is so corrupted that isn't recognized
 > by any MS rtf reader.

The filtered FSK is not reflected in the release notes on the Elecraft
web site.  The capability (enhancement) is still in closed alpha test
and has not been released for open beta.  Contact W0YK for more info.

 > Did they, Elecraft,  have used the 300Hz filter also for TX?

The filtering (or wave shaping) is implemented in the DSP along with
FSK generation much the same as G3YYD's 2tone except the Elecraft FSK
does not need to pass through the audio and separate modulator to get
to RF.

When viewed on the air, the Elecraft FSK bandwidth is in the same
order as 2tone, the new fldigi or MMTTY with TXBPF enabled at 512
tap/300 Hz.  The advantage of Elecraft's frequency shaped FSK is
that there are no audio harmonics or IMD due to sound card output
clipping or mic preamp clipping and absolutely no opposite sideband
or insufficiently suppressed carrier as is common with "AFSK via the
mic jack" in many (most) of the Japanese designed rigs.

The one fault I found with Andy's AFSK work is that he used the K3
with AFSK filter which means his results are not typical of those one
would find with fldigi or 2tone and the tens or thousands of IC706,
IC-746/756/7000/76000, FT-1000MP/2000/3000/5000, TS-2000/870/570, and
older rigs that represent the majority of transceivers in use today.

For examples of overdrive (with an IC-756pro III) or insufficient
carrier/opposite sideband suppression see some of the images at:
        http://www.w1hkj.com/FldigiHelp-3.21/RTTYFSK.html

73,

    ... Joe, W4TV


On 3/22/2013 10:37 AM, Salvatore Irato wrote:
> Hi Andy, great job!
>
> BTW, I don't know if I am late or if I don't remember. But, do you
> have any notice about how Elecraft made this superb improvement?
> I have tried to download theirs FW release notes, but no way by now.
> The .rtf that I could get here is so corrupted that isn't recognized
> by any MS rtf reader.
> It is also unknown to me if those Elecraft release notes cover or not
> what you have explicitly shown to us so effectively
>
> Did they, Elecraft,  have used the 300Hz filter also for TX?
> It seems to that it could be possible, as far as I recall fragments of
> readings here.
> But, I think that this wouldn't be enough to make a so good FSK reshaping.
> Out of any personal speculation it would be really interesting to know.
>
> So if you have any further notice or any clue about how they did I
> will, but also others would, appreciate it.
>
>     73 de iw1ayd Salvo
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