Posted by
P.B. Christensen on
Dec 01, 2009; 7:04pm
URL: http://elecraft.85.s1.nabble.com/K3-killing-RX-key-clicks-tp4093607p4095586.html
> When I first received my Icom 756Pro (now my backup rig) several years
> ago I discovered that the default rise/fall times (adjustable in one of
> the menus) was set to 2 msec (!). That's unconscionable...
It's unconscionable with some rigs, but not all. Take a look at the K3's
keying envelope on a scope since the ca. 3.00 firmware release earlier this
year. Compare it against the QST Product Reviews. I currently measure the
rise time of about 2.5 msec and the K3 occupies minimal RF spectrum. Even
at very fast CW speeds, it's the slope of the rise and fall that primarily
determines occupied bandwidth. As keying speed increases, there's a point
where the keying rate becomes a dominant factor but that's largely due to
the fact that as the keying rate increases so must the envelope slope.
The clicks heard with many transmitters occurs because the slope is
discontinuous. Using a Blackman-Harris or raised-cosine window function
minimizes occupied bandwidth but that function is also dependent on envelope
distortion created by a transmitter's ALC circuitry. So, it's possible to
set two completely different brands of transmitters to 2 msec and the
bandwidth results can be radically different.
Paul W9AC
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