Thomas Martin, DF7TV, Stuttgart, Germany.

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iCW - Internet CW at DF7TV

PacmanDit by DF7TV

Windows 10 Setup for iCW (Testing)

iCW - Internet CW[1], [2] allows for full duplex, QSK conversations using Morse code audio signals in Mumble[3] voice chat. I set up a Mumble[3] client to connect to the iCW Chicago server; address: 216.52.148.10, port: 5360. An Audio Mixer, a RX-Path and a TX-Path are set up on a notebook (Windows 10 Pro 64-Bit). For the connection to the Internet an Ethernet cable is preferred over Wifi. A modification of the K1EL WK3 WinKeyer USB-SMT Kit[13] as presented in Morse Code Circuits is used to get a square-wave side tone signal out of the WinKeyer. This signal is provided to the TX-Path.


Audio Mixer


Select one or more local Hardware Outputs for Audio, switch Receiver CW Regeration ON/OFF

Voicemeeter Potato[4]

Virtual Audio Cable: CABLE Virtual Audio Device[9]Used for Mumble[3] Output / RX-Path

Realtek Line IN - the Side Tone - is the selected device for Voicemeeter Potato Hardware Input 1

CABLE Output (VB-Audio) - the Mumble[3] Output - is the selected device for Voicemeeter Potato Hardware Input 2

Voicemeeter Potato "VAIO3" is selected in Windows "Sounds" as the standard playback device for Windows applications (Mozilla Firefox etc.).

A two-positions macro button "CW Regen" is defined within Voicemeeter Potato to switch CW Regeneration "ON" (using RX-Path - "strip[5") or "OFF" (using the Mumble[3] Output provided via VB-AUDIO's CABLE Output - "strip[1") for reception (by mouse-click on the golden macro button).

Several two-positions macro buttons for Audio Output are defined within Voicemeeter Potato to send the Side Tone (TX-Path) and RX-Output to the selected outputs - "bus[0] to bus[2" (by mouse-click on the blue macro buttons).

A push macro button "Shutdown" is defined to shut down Voicemeeter Potato (by mouse-click on the red macro button) before shutting down Windows 10.

DF7TV iCW Voicemeeter Potato DF7TV iCW Potato Macro Buttons DF7TV iCW Potato Buttons Definitions

Morse Code Signal Shaping Filter


Shape the Morse Code signal in the RX- and in the TX-Path

VST Plugin "EngineersFilter" from RS-MET[6] within Pedalboard2 (32bit) VST Host[5]

A cascade of filters is used to shape the regenerated Morse Code Signal in the RX-Path and in the TX-Path.

Side tone frequency is f_tone = 700 Hz.

Filter 1 (LP) is a 4th order low-pass filter (Papoulis[16]), cut-off frequency = 2 * f_tone

Filter 2 (BP) is a 2nd order band-pass filter (Bessel), BW = 0.39 oct (Q = 3.7), center-frequency = f_tone

Filter 3 (BR1) is a 2nd order band-reject (notch) filter (Bessel), BW = 0.71 oct (Q = 2), center-frequency = 2 * f_tone

Filter 4 (BR2) is a 2nd order band-reject (notch) filter (Bessel), BW = 0.71 oct (Q = 2), center-frequency = 3 * f_tone

The cascade proved to provide a pleasingly sounding side tone at its output, even for the cases of a switched square-wave, triangle or saw-tooth signal at its input. Rise and fall times of the shaped Morse Code signal are at about 6 ms each and are mainly determined by the parameters of the band-pass filter (Filter 2).

DF7TV Morse Code Signal Shaping Filter DF7TV Morse Code Signal Shaping Filter

RX-Path


CW Regeneration

Windows 10, Pedalboard2 (32bit) VST Host -- 1st Instance[5]

Additional VST Plugins from RS-MET[6], SocaLabs[7] and REAPER[8]

Virtual Audio Cable: CABLE Virtual Audio Device[9]

DF7TV iCW setup RX-Path DF7TV iCW RX-Path Settings DF7TV iCW setup RX-Path, VST DF7TV Mumble setup RX-Path DF7TV Mumble setup network

TX-Path


WK3 WinKeyer Side Tone & CW Regeneration

Windows 10, Pedalboard2 (32bit) VST Host -- 2nd Instance[5], WK3 WinKeyer[13] (modified, see Morse Code Circuits) Side Tone Output

Additional VST Plugins from RS-MET[6], SocaLabs[7] and REAPER[8]

WK3 WinKeyer[13] Side Tone Frequency set to 3906 Hz.

External sound card: Behringer U-Control UCA222[10], Behringer ASIO Audio Driver 2.8.40. Driver retrieved from DROPBOX -- for 32-Bit: [11] and for 64-Bit: [12]

RTL Utility[15] was used to measure the Round Trip Latency (sum of the Output and Input delays) of the UCA222 to be abt. 9 ms (at sample rate = 48000 Hz, audio buffer size = 48 samples and using the Behringer ASIO Audio Driver 2.8.40). The UCA222 makes use of a Burr-Brown Stereo Audio Codec PCM2902[14]

Audacity - Audio Editor and Recorder[17] is used for signal analysis.

DF7TV iCW setup TX-Path DF7TV iCW setup TX-Path DF7TV iCW TX-Path Settings DF7TV Mumble setup TX-Path

The letter "V" sent at 40 wpm (f_tone = 700 Hz) and then received as a .wav-file from the Mumble Loopback test server:

DF7TV Letter V sent and received

Presented is a short recording of the output of the TX-Path at a speed of 40 wpm (f_tone = 700 Hz) as received from the Mumble Loopback test server:

This is the spectrum of the recording at 40 wpm (f_tone = 700 Hz):

DF7TV TX-System output spectrum

References

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