Fldigi
can send and receive morse code from 5 wpm to 200 wpm. The
operating controls for CW are found on the Config/CW tab. You can
open that tab by selecting the "Configure/Modems" menu item and the
clicking on the Modems/CW tab. You can also open up the CW tab by
first selecting CW as the operating mode and then clicking on the
left-most item "CW" on the status bar at the bottom of the fldigi main
window. During operation the Rx and Tx WPM settings are
annunciated on the status bar in the two boxes next to the mode
indicator.
The CW decoder has a DSP filter than is implemented with a sin(x)/x impulse response. This is a very steep sided filter that is centered on the received signal in the audio passband. You can control the bandwidth of this filter using the BW control.
Fldigi can track the incoming signal. Enable Rx WPM tracking by enabling the check box "Enable Tx Trkg". The tracking range (+/- Hz around the TxWPM setting) can be set using the "Rx Trkg Rng" control.
The RxWPM controls are indicators and are not used for setting the operation of the CW decoder.
The TxWPM sliding controller is used to set the transmit WPM. To make the setting easier two additional controls are provided. "Lower" sets the lower limit of the slider and "Upper" sets the upper limit of the slider. The resolution of the TxWPM slider is 1 WPM. The Lower/Upper controls are in in 5 WPM increments.
The transmit encoder settings for WPM can also be adjusted with three hot keys:
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 A2 signal is completely generated in the software so it is possible to control many aspects of the CW signal.
Many QSK operators use high speed diode antenna switching between receiver and antenna. fldigi generates a signal that can be used for that purpose. The left audio channel is always the AFCW signal. When selected the right audio channel can be configured to generate a square wave signal that begins earlier and ends later than each of the CW elements. The square wave signal can be rectified and filtered to provide the diode switching signal for the Rx/Tx antenna switching.
The right audio channel QSK signal is selected by checking the box and then adjusting the pre and post timing in millisecond increments. See CW Keying for additional information and a circuit which converts this signal into a keying waveform.
Operating CW and additional notes on CW configuration is described in Operating CW.
Setting up a QSK device can be quite difficult. Fldigi helps to ease the adjustment by generating a continuous series of characters. This allows a dual trace scope to be properly synched while making the adjustments to both the software and the associated QSK hardware. You enable continuous characters by selecting the checkbox, and then enabling the T/R button for transmit. The repeated character can be change on the fly with the pick control. It can be one of either E, I, S, T, M, O or V.
The CW decoder has a DSP filter than is implemented with a sin(x)/x impulse response. This is a very steep sided filter that is centered on the received signal in the audio passband. You can control the bandwidth of this filter using the BW control.
Fldigi can track the incoming signal. Enable Rx WPM tracking by enabling the check box "Enable Tx Trkg". The tracking range (+/- Hz around the TxWPM setting) can be set using the "Rx Trkg Rng" control.
The RxWPM controls are indicators and are not used for setting the operation of the CW decoder.
The TxWPM sliding controller is used to set the transmit WPM. To make the setting easier two additional controls are provided. "Lower" sets the lower limit of the slider and "Upper" sets the upper limit of the slider. The resolution of the TxWPM slider is 1 WPM. The Lower/Upper controls are in in 5 WPM increments.
The transmit encoder settings for WPM can also be adjusted with three hot keys:
- Numeric keypad "+" increases the TxWPM by 1
- Numeric keypad "-" decreases the TxWPM by 1
- Numeric keypad "*" toggles between the selected TxWPM and a default WPM
- Wt % control sets the weight of the CW. Normal CW is at 50% weight, ie: a dot is equal to the interval between dots or between code elements. It has a range of 20 to 80 percent.
- Dash/Dot controls the relative weight between a dash and a dot. The standard for CW is 3 to 1. The dash is 3 times the length of a dot. Some operators prefer the sound of either a heavier or lighter sounding CW. This control can be adjusted from 2.5 to 4.0 in 0.1 increments.
- Edge shape provides two leading/trailing edge shapes (1) Hanning, or raised cosine, and (2) Blackman a modified raised cosine with a steeper attack and decay. Both of these edge shapes give a more narrow bandwidth CW signal than the traditional exponential waveform. They are very easy to listen to even at speeds exceeding 100 wpm.
- The Edge control sets the rise and fall times of the CW waveform. It can be set anywhere from 0.0 to 15.0 milliseconds in 0.1 millisecond increments. DO NOT operate A2 CW with the control set below 4 msec. This is the control that sets the effective bandwidth and sound of your CW. If the edge is too steep you will have a clicky signal and be the bane of the CW bands. The purpose of being able to set the edge to 0.0 or a very quick rise/fall time is explained below. A good setting for nice sounding CW at 40 WPM and below is 4 to 6 milliseconds.
- Edge decreases pulse width, when checked will give a slightly narrower dot length as the edge timing is increased. This is useful when operating QSK and listening between the character elements.
QSK
You might ask why fldigi doesn't simply provide a keyline output on one of the parallel port pins or on RTS or DTR via a comm port. The answer is quite simple. Linux is a multi-tasking operating system and the interaction between the OS and the application causes the timing to be adversely effected. The driver implementation of the audio sub system must be responsive and so the OS gives that sub system a very high priority in its multi-tasking structure.Many QSK operators use high speed diode antenna switching between receiver and antenna. fldigi generates a signal that can be used for that purpose. The left audio channel is always the AFCW signal. When selected the right audio channel can be configured to generate a square wave signal that begins earlier and ends later than each of the CW elements. The square wave signal can be rectified and filtered to provide the diode switching signal for the Rx/Tx antenna switching.
The right audio channel QSK signal is selected by checking the box and then adjusting the pre and post timing in millisecond increments. See CW Keying for additional information and a circuit which converts this signal into a keying waveform.
Setting up a QSK device can be quite difficult. Fldigi helps to ease the adjustment by generating a continuous series of characters. This allows a dual trace scope to be properly synched while making the adjustments to both the software and the associated QSK hardware. You enable continuous characters by selecting the checkbox, and then enabling the T/R button for transmit. The repeated character can be change on the fly with the pick control. It can be one of either E, I, S, T, M, O or V.