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From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <DUB114-W527B4B9708FCDF5FD0ABC5D3460@phx.gbl> <520F60AF.2000004@iup.uni-heidelberg.de> <0127125B54F94B748D9AC87A4A813300@Clemens0811> <5210BB04.9000401@iup.uni-heidelberg.de>
In-Reply-To: <5210BB04.9000401@iup.uni-heidelberg.de>
Date: Sun, 18 Aug 2013 22:15:03 +0200
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Subject: RE: LF: QRM on 472.5kHz
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Status: O

Hi Stefan,=20

>But why did you=20
>write that email at 10 hours after the QSO took place? When beeing in=20
>the shack, i'm mostly watching incoming emails

I was unsure if you would do that, so I decided to resort to listening =
to
the
interesting stuff you were talking about (antennas,drinks, girls...:-) =
).

>And they all use true class D PAs.
>Somehow most of the active CW stations do not have a "clean"=20
>signal and=20
>those who have a clean signal are not QRV :-)

I have no hands-on experience with class D PAs,only class B,
but it seems that key klicks with class D are NOT inevitable,see
http://amfone.net/Amforum/index.php?action=3Dprintpage;topic=3D28417.0
Quoting from there:
---------------------------
"...Well, I know from the tube days that you couldn't just key the drive =
to
a tube class C final - major key clicks.  The same goes for class C, D =
or E
solid state amps.  You can't just key the drive - same problem - key =
clicks.
This is because the shape of the keying waveform is not preserved in =
class
C, D, E or F due to the fact that the amplifiers are not linear (nor =
should
they be!!).

"Overshaping" of the input waveform is NOT recommended with MOSFETs =
because
they have so much gain.  A parasitic can result when the MOSFETs are
operating in the linear region.  And if you are using digital drive =
(which
is a better way of driving MOSFETs) you can't even overshape the input.

So, what is generally done is to key the drive and key the high voltage
using a series element (a MOSFET or MOSFETs in parallel) - with the =
input to
the series element being a good CW rise and fall time.  The series =
element
is most easily created using a source follower and some type of pull up =
with
controlled rise and fall times.  Easy to do with simple R/C circuits. "
------------end of quote--------------------

So my main point is that it should be doable for a serious homebrewer to
generate a (nearly) key klick free CW signal also with a class D amp.
The stronger the signal the more important is a clean spectrum.

>Did you listen by ear or did you use a CW decoder?

My aural limit is at about 12-15wpm and you were going near 30wpm...
My compliments!

73
Clemens
DL4RAJ=20
=20
=20
>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org=20
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan =
Sch=E4fer
>Sent: Sunday, August 18, 2013 2:16 PM
>To: rsgb_lf_group@blacksheep.org
>Subject: Re: LF: QRM on 472.5kHz