K2: audio thumps and pops on key closure - is K1 app note relevant?

[VK7JB]

Hello Group,

I've been using my K2/100 on CW a bit lately and have noticed that there are low frequency thumps/pops on the receive audio at the rx to tx transition - ie onset of keying (key closure).  They are most noticable if the noise floor is high or if there are other signals in the receiver passband.  If I wind the RF gain right back or operate on a really quiet band and the artefacts disappear.  

They don't relate to the DSP (they occur even when DSP is bypassed), to the state of the 8R Hold parameter or to the presence or absence of transmitted RF (the artefacts are present also in TEST mode).

I see there is mention of this issue in the K1 in an application note found here:

http://www.elecraft.com/Apps/K1_qsk_app_note.htm

It describes what I hear in my K2.  Does anyone know if there is a similar mod for the K2, or whether this K1 mod might be relevant to the K2 if adapted?

Thanks for any ideas.

73,
John
VK7JB

[Don Wilhelm-4]

John,

A long time ago, there were pops and thumps with keying in a few K2s
having the KDSP2 and KPA100 options.  It was coming from the KPA100 T/R
switch, and several changed capacitor values in the KPA100 to combat it.

Check your KPA100 - if it has red toroid cores at L15 and L16, then
adding KPA100UPKT would be the first order of business.

I have not seen mention of a K2 parallel to that K1 mod - you could try
it, but you would need two caps and two resistors - connect to the drain
of Control Board Q7 and Q8.

73,
Don W3FPR

On 4/15/2012 12:56 AM, VK7JB wrote:

> Hello Group,
>
> I've been using my K2/100 on CW a bit lately and have noticed that there are
> low frequency thumps/pops on the receive audio at the rx to tx transition -
> ie onset of keying (key closure).  They are most noticable if the noise
> floor is high or if there are other signals in the receiver passband.  If I
> wind the RF gain right back or operate on a really quiet band and the
> artefacts disappear.
>
> They don't relate to the DSP (they occur even when DSP is bypassed), to the
> state of the 8R Hold parameter or to the presence or absence of transmitted
> RF (the artefacts are present also in TEST mode).
>
>

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[VK7JB]

Thanks Don.  This is a relatively new K2/100 # 6998 and the KPA100UPKT mod has been incorporated, as far as I understand.

I'll try the resistor & cap mod to the drains of the mute  FETs on the K2 control board and see what happens.  

73,

John
VK7JB