Posted by
Jim Brown-10 on
Jun 09, 2020; 7:45pm
URL: http://elecraft.85.s1.nabble.com/CW-rise-time-setting-tp7661876p7661948.html
On 6/9/2020 11:07 AM, Al Lorona wrote:
> The reduction in the sideband levels (what some folks here called 'clicks'... not sure that's a good name for this) varies depending on where you measure it, but in general the sidebands will drop anywhere from 0 to 12 dB-- sometimes less, sometimes more-- when you go from 2 msec to 8 msec rise/fall times. For instance, arbitrarily choosing an offset of 500 Hz from the carrier, the sideband drops by 11 dB for the longer rise time. That turns out to be a fairly typical value. And by the way, in general the sigmoid does a better job than a raised cosine.
I've not looked at the math, but I've measured more than a half dozen
radios, most with variable time constant shaping, and Elecraft with
their fixed sigmoidal shaping. The data is here.
http://k9yc.com/P3_Spectrum_Measurements.pdfA K3 at 25W (driving a KPA500 to full power) is 50 dB down 230 Hz either
side of the signal, 60 dB down at 305 Hz. At 40W driving a legal limit
tube amp (Ten Tec Titan) sidebands at the power amp output are 50 dB
down at 235 Hz, 60 dB down at 335 Hz.
A neighbor's FT1000 Mark V Field was 50 dB down at 665 Hz.
Another neighbor's FTDX5000 set for 6 msec was 50 dB down at 410 Hz, 60
dB down at 1.05 kHz before the firmware update. It improved to -50 dB at
310 Hz and -60 at 535 Hz after the update.
73, Jim K9YC
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