[Elecraft] CW rise time setting

Wed Jun 10 09:34:19 EDT 2020

Jim,

Interesting results, especially the dramatic difference in the FTDX5000 after the firmware update. The K3 looks great. Hopefully the K4 will be at least as good.

Ed / w2rf

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of Jim Brown
Sent: Tuesday, June 9, 2020 3:46 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] CW rise time setting

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.pdf> http://k9yc.com/P3_Spectrum_Measurements.pdf

A 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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