Re: K3: killing RX key clicks
Posted by
Jan Erik Holm on
Dec 02, 2009; 5:06am
URL: http://elecraft.85.s1.nabble.com/K3-killing-RX-key-clicks-tp4093607p4098066.html
Paul Christensen wrote:
>> 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
>
Are you sure about 2.5 ms? As far as I remember I measured my K3
to about 5 ms and Elecraft also stated 5 ms. This was over a year
ago however, if 2.5 is correct they have changed it or my memmory
is corrupted.
/ SM2EKM
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