[Elecraft] RE: K2DSP puzzle

[Ken Wagner]

I am observing a similar thing here with the KDSP in #3571. However, I'm
guessing that it is not as severe as Brendan is reporting, because I hear
the l'il pop intermittently and not with each and every Rx->Tx transition,
and I don't hear it at all when the KDSP is in Bypass mode.
73,Ken K3IU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
----- Original Message -----
From: "Brendan Minish" <ei6iz@newsguy.com>
To: "Lyle Johnson" <wa7gxd@fidalgo.net>
Cc: <elecraft@mailman.qth.net>
Sent: Thursday, July 17, 2003 11:12
Subject: [Elecraft] RE: K2DSP puzzle


| Hi Lyle,
|
|          I think you misunderstand the problem slightly, the pop is caused
| by an abrupt truncation of the RX audio by the K2 mute circuit when going
| into transmit.
|
| slowing down the QSK speed only helps a little since we no longer open the
| RX as often (& by extension have less RX -> TX transitions) but it does
not
| solve the problem.
|
| one solution would be to slow down the action of the mute circuit so that
| it does not make quite such an abrupt transition when muting the RX audio,
| one other option would be to delay the mute by a few msec more but this
| would probably require a K2 firmware change and in any case the timing on
| the K2 MCU may be too ' granular '  to allow for this.
|
| in the normal non DSP arrangement the k2 ramps the RX audio down over a
few
| cycles about 4 or 5 msec before the mute circuit comes on, the mute
release
| is shaped C23 and R17 which is why reducing R17 (to speed up the QSK ) too
| much can cause a similar problem.
| The additional delay due to the DSP processing time means that the mute
| circuit comes on before the ramped down RX Audio makes it out of the
filter.
|
| Unfortunately the delay in bypass mode is still long enough to cause
problems
|
| As for how the K2 sounds on QSK without the DSP installed. it's very
| smooth, the side tone sort of feels like another signal on the band. On my
| k2 you cannot actually hear between the dots much above 25 WPM but you can
| hear between the letters fine.
| Smooth QSK is rare and it is one of the (many!) really nice things about
the K2
|
|
|
| At 15:34 17/07/2003, you wrote:
| >Hello Brendan!
| >
| > > Any ideas for a mod to fix this?
| > > Slowing down the onset of the mute circuit slightly should do it but I
am
| > > not sure how best to go about this.
| >
| >All the muting is handled externally to the KDSP2.  It has its own
muting,
| >but that is currently only invoked during during power up, to elimninate
a
| >loud POP that would otherwise leave your ears ringing for a while!
| >
| >Signals do take a while longer to propagate through the KDSP2. The
sidetone
| >is injected after the KDSP2.  Adding delay to the unmute function would
| >probably slow down the K2's top speed for effective QSK, but that may be
a
| >trade-off you're willing to accept to get around the problem you cite.
| >
| >Since I don't personally operate QSK CW, I am not the right person to
work
| >out a mod to get around the problem.  WHat sounds right to me might not
| >sound right to you, and I have no real frame of reference as to what it
| >*should* sound like.
| >
| >In any event, to slow down the unmute process, increasing the value of
C23
| >on the control board would probably be the most direct route.
| >