[Elecraft] QSK THUMPS?

[Guy Olinger K2AV]

One of the issues found in QSK operation is that TX-RX state changes
MUST modulated the received envelope. It is a fact that the RX stream
must be turned off, and then turned on, to support transmitting and
that is a modulation. The RX is ON after the latter state change and
will hear the modulation. The only way to modify that modulation is by
changing the shape and rise/fall times.  This is the point at which
the desire to hear between bauds, and to not hear artifacts of the
state changes, are at odds with one another.  A slower transition does
less modulation, but slower can cause the transition to exceed the
baud space, defeating the reason for QSK in the first place.

To have clean hearing between bauds at 25 WPM does not allow time for
soft and no-thump transitions.  If there is anything being received,
then the modulation of the RF envelope creates sidebands.  The wider
the energy being modulated, the greater likelihood of modulation
sidebands. Set TX TEST, CW mode, QSK, then turn MON all the way down.
Now hold down dits with your paddle and tune across a loud signal of
any kind. Loud carrier between 7.2 and 7.3 is a good test.  Most of my
friends call that thumps, particularly if there is a really loud
signal in the passband.  This change is being imposed as far forward
as the PRE/ATT.  If you study the schematics, a lot of RF and 1st IF
circuitry is either being switched out or reversed, thus imposing the
modulation at points of mandatory artifact sideband generation.

Having said that....

Now turn the RX EQ to -16 in bands 1 and 2 and note the large drop in
the amplitude of the "thump".  Also note (if you have the roofing
filters for this) that the thumping is quite more pronounced with wide
roofing filters than narrow.

This is one instance where having headsets with hi fi response down to
15 Hz is no advantage.

73, Guy.


On Wed, Apr 28, 2010 at 1:01 PM, The Smiths <notforchat at hotmail.com> wrote:
>
> You'll find that the louder the noise floor the worse the thumping. Again, reducing your RF gain, Turning on your NB and NR will help the thumping go away.
>
> It's possible that when you started hearing the problem the noise floor had risen up some, and then when it went away it had reduced again..
>
>> Date: Wed, 28 Apr 2010 05:00:36 -0700
>> From: lstavenhagen at hotmail.com
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] QSK THUMPS?
>>
>>
>> I heard this too during a QSO not too long ago. It was intermittent tho and
>> just started happening in the middle of the QSO. I was keying the rig
>> through the USB->rs232 adapter with RUMLog's keyer at about 20wpm, I thought
>> something had suddenly gone wrong. It did go away tho as the QSO went on...
>>
>> I can't reproduce it with the build-in keyer plus paddles into a dummy load
>> at any power setting. Perhaps I'll have another go with this with the
>> computer and see what happens.
>>
>> Interesting....
>>
>> 73,
>> LS
>> W5QD
>> --
>> View this message in context: http://elecraft.365791.n2.nabble.com/QSK-THUMPS-tp4971836p4974029.html
>> Sent from the [K3] mailing list archive at Nabble.com.
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