[Elecraft] Filters and Configuration Questions

[Guy Olinger K2AV]

I'll vote with Bill here.

Since the CW envelope in the digital number stream is pristine, the
filters and any envelope delay can only distort it. In the case of the
2.7, the delay is far enough away frequency-wise from the signal to be
insignificant.

Given that the filters are subject to manufacturing variance, and a
super clean filter would be prohibitively expensive, to use a narrow
one would involve some kind of routine to "reverse modify" the CW
envelope number stream to the transformative opposite of the
distortion, so that the delay undoes its distortion by distorting it,
kind of like two amps in series that together have less IMD than
either alone, common enough.

While that is attractive in a geeky way, it would have to be done on a
bench for the exact filter.

Given the results we have, aside from unfortunate and now-fixed issues
such as the microphonic sensitivity of the VCO boards, CW is
remarkably clean. It's the only rig available to me I would consider
using to park on 7000.25 as a run frequency.

It MAY be that Wayne et al have some of that reverse magic in effect,
but I haven't heard of it.

Trying to fix something that ain't broke?

73, Guy.

On Wed, Jan 5, 2011 at 11:19 AM, Bill W4ZV <btippett at alum.mit.edu> wrote:
>
>
> P.B. Christensen wrote:
>>
>> Since keying bandwidth is a function of the RF envelope shape, I'm not
>> sure
>> why anyone would want to narrow the K3 filter on CW transmit.
>>
>
> Because most rigs have spurs and I wanted to make my signal as clean as
> possible.  Typically these may be <80 dBc but still readable if the
> transmitter is using high power and the receiving station has good antennas
> (e.g. on 160m in particular).  I often hear +/- 1 kHz -80 dBc spurs from
> FT1000 series rigs and of course the 2.4 kHz -60 dB spur from the Flex 5k
> (recently fixed thanks to W5ZN and others' persistence).
>
> If you look carefully at Figure 2 in ARRL's original K3 product review, you
> can see a few suspicious blips which I wanted to clean up.  Unfortunately
> using 1 kHz to TX in the K3 caused other problems so I abandoned the idea.
>
> I'm not aware of any spur reports on the K3 since the VCO stiffener and KPA3
> mods were implemented, so I agree there's probably no need now.
>
> http://www.elecraft.com/manual/ELECRAFT%20KSYN3%20Stiffener%20Mod%20Rev%20D.pdf
> http://www.elecraft.com/K3/mods/K3%20Technical%20Alert%201.pdf
>
> For any interested in assuring clean signals you should also consider the
> chirp mod (if applicable):
>
> http://www.elecraft.com/K3/mods/KSYN3%20DDS%20Gain%20Modification.pdf
>
> 73,  Bill
>
> --
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