CW Mode

Fldigi generates CW using AFCW (A2).

AFCW, A2 is generated by tone insertion into a transceiver operating in either USB (preferred) or LSB mode.  The actual transmitted signal will be at the USB carrier + the audio frequency, or the LSB carrier - the audio frequency.  If fldigi is tracking and receiving a CW signal on the waterfall your transmitted signal will be exactly on the frequency of the other operator.  The CW generated this way has a nearly ideal attack and decay time, controlled by the software modem.  But ... a caveat ... your transmitter must never be overdriven and it should have excellent opposite sideband suppression.  Overdriving the transmitter can cause multiple audio signals within the SSB passband, and cause unwanted interference to other ops.  The same is true for a poorly designed or adjusted transmitter with bad sideband suppression.  I recommend having a trusted and knowledgable operator assist you when first trying A2 CW.  Have them carefully look for evidence of your signal above and below your primary signal (by at least +/- 3 Khz).  If there is no evidence of extra signals then your are set to go.  If there is you might want to have the transceiver adusted for sideband suppression, or check to be sure you are not over driving the audio.

This is what the A2 signal should look like with various settings of weight, Dash/Dot and Edge.  The audio frequency is 400 Hz and the TxWPM is 100 WPM.


Dash/Dot = 3.0, Edge = 0.0
Dash/Dot = 4.0, Edge = 0.0

Dash/Dot = 3.0, Edge = 3 msec
Dash/Dot = 3.0, Edge = 6 msec

Dash/Dot = 3.0, Edge = 12 msec

Changing the weight, dash/dot or edge of the waveform does not change the WPM at which the code is generated.  When a conflict occurs between the various settings WPM takes first priority, and Edge second.  In the above examples, the Edge setting could not exceed 12 msec even if the control were set higher than 12.0.  The figures were generated by capturing the output data being sent to the sound card and then formatting it using Gnumeric.  An oscilloscope photo of the signal is virtually identical.

The setting for inter-character and inter-word spacings are fixed at 3 and 7 respectively.  The 3 is achieved by sending a silent period of 1 dot (element) length at the beginning of each character and 2 at the end of each character (shown in the figures).  This silent period is sufficient for most transceivers to respond to the PTT signal which occurs at the beginning of the transmission so that the first dit or dash is not lost in transmission.QRQ (high speed CW operation)

You may wonder why fldigi can go as high as 200 WPM.  It's hard to believe but there are CW operators who can decode 100+ WPM in their head.  These operators also usually operate QSK (full breakin).  A2 CW and PTT operation and QRQ/QSK are not a natural mix.  But fldigi can be used for this type of operation if an external keyer is used.  For that purpose the A2 Tx output from fldigi is full wave rectified and detected to create a keyline control.  The outboard conversion from A2 to keyline requires a nearly square wave pulse output of audio at the CW keying rate.  Setting the Edge control to 0.0 and then the audio frequency to about 1000 Hz provides the needed signal to effect this type of keyline control.

If you are operating QSK with a separate receiver / transmitter you can very quickly stop your transmit signal with the TAB key.  In the CW mode only the TAB key causes the program to skip over the remaining text in the transmit text buffer.  The text that is skipped will be color coded blue.  The program remains in the transmit mode (PTT enabled), but since the buffer is now empty no A2 CW signal is generated.  Code transmission will then restart with the very next keyboard closure of a valid CW character.  The Escape and Pause/Break keys still can be used to respectively abort and pause transmission.

CW Prosigns

The prosigns available in the CW mode are:

PROSIGN
 KEYBOARD
 DISPLAYED AS
AA ~ <AA>
AR } <AR>
AS % <AS>
HM ^ <HM>
INT & <INT>
SK
 >
 <SK>
KN
 <
 <KN>
VE
 {
 <VE>

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