Re: K3: killing RX key clicks
Posted by
gm3sek on
Dec 01, 2009; 11:27pm
URL: http://elecraft.85.s1.nabble.com/K3-killing-RX-key-clicks-tp4093607p4097008.html
Joe Subich, W4TV wrote:
>
>
>> Clicks are a function of a FAST RISE TIME and DISTORTION, not
>> keying speed.
>
>Not quite ... keyclicks are often a second derivative effect.
>They occur when the rate of change of the rate of change is
>high - specifically at the "corners" of the waveform (a abrupt
>change in the slope coupled with high power levels).
>
>At one time W8JI had some scope and spectrum samples of CW
>waveforms with "slow" rise/fall rates but very bad clicks.
>In every case the ramp was fine but there was an abrupt change
>when the ramp reached the steady state (on) condition or at
>instant of transition from the steady state (on) condition to
>the start of the decay phase.
>
Correct - both the overall rise/fall time and absence of sharp corners
are important. W9CF shows that an optimum wave shape has a gradual
start, accelerating to a more rapid rise/fall through the middle part,
and then slowing to a more gradual finish.
The 'RC rise/decay' wave shape that was in the handbooks for many years
is actually a *bad* shape because it has a very sharp corner on key-up.
Another factor that can cause nasty key-clicks from a K3 is the default
TX delay of 8ms. This may not be enough time for some amplifiers to
change over, causing clicks due to hot-switching. This time can be
increased using CONFIG / TX DLY.
--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek______________________________________________________________
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