Extreme QRQ CW sending(keying) with the ELECRAFT K3 - 200 wpm with incredible accuracy and performance

Using LINUX MINT 17.3 and some free DSP AUDIO LV2 Linux plugins...it is possible to get better cw keying on your Elecraft K3 and more versatility by bringing in the ability to use your ST KEY and IAMBIC PADDLES ... while preserving fast QSK full break in.

This is done by using AFCW A2 CW MODE and injecting a CW AUDIO TONE into the K3's own USB SOUND card input...BUT FIRST activating the PTT(so the K3 is operating without VOX)

The timing of both the PTT and when the CW AUDIO TONE arrives to the K3 soundcard is critical. The settings are shown for what works on my setup...through trial and error while watching the RF K3 OUTPUT on an oscilloscope and recording the K3 SIDETONE(audio monitor from the K3) observing, making changes, re-testing...etc...

After FLdigi sends cw at 200 wpm, EXTREME STRESS TEST for the K3 TO XMIT CW at such a high speed, a recording of what was sent...is shown , so you can visualize the 200 wpm cw waveforms and see how well the K3 does at sending at this extremely high speed using AFCW A2 MODE(note: this would not be possible using normal a1-mode normal K3 cw jack keying on the K3[s)

Using 2 instances of the Xchat plugin - cwirc - i was able to use both iambic paddles and a straight key using 2 different serial ports...the included serial port on the computer and then adding a 2nd serial port via a USB to SERIAL PORT ADAPTER(prolific driver)

To wire up all the apps and get everything where it needs to go, jack audio does the job well...AND using multiple pulseaudio jack-sink modules...where you can individually name each jack-sink ..it is easy to connect the outputs and inputs to all the apps you see at the end of the video...inside the JACKROUTER CONNECTION BAY

1. the PTT needs to be activated first on the K3...using an audio derived cw keying circuit...the output of a USB SOUND CARD, is directed towards the input of the ADCWKC ...the output grounds the PTT JACK of the K3 for the normal time of the cw element PLUS an additional 75ms(still leaves plenty of qsk HF receive audio between letters or words...depending on how fast you're sending)

to hold the PTT SWITCH open for another 75 ms, TEST TONES and CALF GATE are used...the TEST TONES audio output is about 10 db's below the gate threshold by CALF GATE attenuating its input until a higher volume from the ST KEY, PADDLES, or FLDIGI CW KEYBOARD sends their tones...then that will make the GATE OPEN and pass the CW TONES from the ST KEY, PADDLES or FLDIGI and then after the cw note is finished, TEST TONES audio output(3khz) keeps the PTT CLOSED until the 75 ms holding time is finished...then the CALF GATE turns off and the K3 PTT turns OFF.

The quality and volume of the actual cw audio notes that goes to the K3 USB sound card LINE INPUT, is VERY CRITICAL, you have to look at your RF wave form on your scope and then lower your volume until you see the RISE TIME EDGE of your cw note go from a SPIKE to a smooth curve - as it should be.... on my system it took about 40 to 50 db's of attenuation of the cw audio note, to remove any rise time edge spikes on the RF ENVELOPE as seen on the scope. You do NOT want the K3 ALC to activate...and even if you can't see any ALC action on the K3 METERS... you can still have significant RISE TIME SPIKES on your RF OUTPUT ...so you have to lower the volume of your audio input to the K3 USB SOUNDCARD until the SPIKE is no longer seen on the rising edges of your cw notes... even with this low amount of volume, i was able to get FULL POWER out of the K3. Also....do a spectrum analysis of your cw notes in general - using any of the free audio spectrum analysis LINUX APPs and make sure your spectrum is very clean with no harmonic spikes above the pitch of your cw note.

This is not an exhaustive HOW TO tutorial, but an introduction to an advanced setup that i thought was well worth the learning curve...having all my morse code instruments available for keying the K3, being able to have better, faster QRQ & QSK than usual, and routing the audio through the computer software so i can control it, apply DSP to it etc...i thought that there are some significant advantages for sending and copying cw this way on the ELECRAFT K3.

NOTE: grig can be used, so you do not have to move from the computer station, to the RIG to change your frequencies...

NOTE:   here is a scope shot  of how to make sure you are not over driving the K3 USB LINE INPUT with too much cw audio volume output from the sine wave morse code generator APP:   lower the volume until there are no spikes

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Comment by Joe on November 29, 2016 at 9:38am

Wow, fascinating stuff, Chuck. I will have to read this a few times before I get it all, though. Unfortunately, my K3 is still in the distant future. Since the Bank of Dad morphed into the Bank of Granddad, I will be using my old Ten Tec Omni D for a while yet!

Joe W3GW


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