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