CW rise time setting

[ANDY DURBIN]

"I repeat my advice that keying characteristics must be evaluated in the FREQUENCY domain (as occupied bandwidth), NOT in the TIME domain (oscilloscope). The reason has been stated here many times -- it's not only the TIME of the transition that determines bandwidth, it is the SHAPE of the transition from off to on and on to off that matters, NOT the time it takes, and this cannot be seen on a scope."

The frequency domain will have no information (other than lack of signal) until RF is generated.  A spectrum analyzer cannot be used to determine the timing of the various switching events during CW keying.  It can only provide useful information while RF is being generated.

Your post was in reply to "Thanks for the scope shot and info. I compared the waveform to the QST K3S review, which seems to show a little over 10ms before RF appears. Is this because they used different settings?"  This appears to relate to the timing of the switching events not to the characteristics of the RF itself.  I think the oscilloscope is the right instrument for this measurement.

I would submit that both a 'scope and a spectrum analyzer are required for a full evaluation of keying characteristics.

73,
Andy, k3wyc
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Edward H Russell]

In computer space 4ms is an eternity. I do wonder what is going on there. And also hope the K4 fixes it. Thanks again for the scope shot.

 

Ed / w2rf

 

 

 

From: Bob Wilson, N6TV <[hidden email]>
Sent: Friday, June 12, 2020 10:37 AM
To: Elecraft Reflector <[hidden email]>
Cc: E.H. Russell <[hidden email]>
Subject: Re: [Elecraft] CW rise time setting

 

The plot in the QST review of the K3S shows the delay between "key closure" (the KEY jack of K3S) and RF out.  My plot shows the delay between "amp relay closure" (the KEY OUT jack of K3S) and RF, which is more critical.

 

Most folks assume there will be no delay between KEY closure and KEY OUT closure, but there is an extra delay (of about 5 ms, minimum) in the K3S.  The same applies to PTT IN closure and KEY OUT closure; that is, there is an unexplained fixed 5 ms delay in the K3S, probably due to slow firmware logic testing for TX Inhibit or an intentional enforcement of some minimum delay in RF output.

 

Most radios close KEY OUT immediately upon key closure of either the KEY jack or the PTT IN jack.  The K3 does not; it "hesitates" before closing KEY OUT.

 

I'm also hoping the K4 will eliminate this unusual behavior.




73,

Bob, N6TV

 

On Fri, Jun 12, 2020 at 3:23 AM E.H. Russell <[hidden email] <mailto:[hidden email]> > wrote:

Bob,

 

Thanks for the scope shot and info. I compared the waveform to the QST K3S review, which seems to show a little over 10ms before RF appears. Is this because they used different settings?

 

Will be interesting to see how the new radio CW looks in time and frequency domains. Also how the turnaround latency is managed.

 

Tks,

73 Ed w2rf

 

 

 

From: Bob Wilson, N6TV <[hidden email] <mailto:[hidden email]> >
Sent: Thursday, June 11, 2020 2:05 PM
To: Elecraft Reflector <[hidden email] <mailto:[hidden email]> >
Cc: E.H. Russell <[hidden email] <mailto:[hidden email]> >
Subject: Re: [Elecraft] CW rise time setting

 

On Mon, Jun 8, 2020 at 12:31 PM E.H. Russell <[hidden email] <mailto:[hidden email]> > wrote:

I suppose shaping of the curve corners removes harmonics introduced by the abrupt transitions, allowing an accelerated ramp inbetween. But does this really reduce the total rise time to 2.5ms? It seems that the softening process must take some time. Wish I had a K3 here to scope against other radios. Anything published out there?

 

Ed,

 

Per your request, I am publishing this scope screen capture which plots the CW rise time in my K3 with the KSYN3A synthesizer upgrade.  It's about 4 ms from 0 RF to full RF (2 ms per horizontal division):

 

https://www.kkn.net/~n6tv/N6TV_K3_Ser_1494_FW_05.64_TX_DLY_8_CW_QRQ_OFF.png

 

The vertical markers are there to illustrate that CONFIG:TX DLY nor 008  provides only about 6 ms of RF delay after "KEY OUT" goes to ground, not 8 ms, and there is jitter in that delay as well (not shown).  If CW QRQ mode is enabled, the delay drops to about 4.6 ms and the TX DLY setting is completely ignored.

 

This was discussed here two years ago.  See this post for suggestions on how to avoid hot-switching a non-Elecraft amplifier driven by a K3 or K3S:

 

http://elecraft.365791.n2.nabble.com/Default-K3-transmit-delay-may-be-too-short-for-slow-QRO-amplifiers-td7641779.html 

 

73,

Bob, N6TV

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]