dl-fldigi/fldigi_doxygen/user_src_docs/configCW.txt

/**
\page cw_configuration_page  CW Configuration

\tableofcontents
<br>
\image html config-cw-general.png "General CW Configuration"
\image latex config-cw-general.png "General CW Configuration" width=5.0in
<br>

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.<br>

<br>The CW signals are converted to a baseband signal. It is the
digital equivalent of tuning an analog USB transceiver so that the
carrier is exactly at the CW carrier frequency. The CW decoder
can use one of two different DSP filters. The Fast Fourier
Transform (FFT) filter is implemented with a sin(x)/x
impulse response. This is a very steep sided low pass
filter. Unchecking the FFT filter causes the decoder to use a
Finite Impulse Response (FIR) filter with a cutoff slope that is not as
steep. The FFT filter is optimum when receiving CW in a white
noise environment. The FIR filter may give better response with
impulse noise. Selected a "Matched" filter for either the FFT or
FIR implementation optimizes the filter bandwidth for white noise
suppression. A lot of impuse noise (static) can cause either
filter to ring and increasing the filter bandwidth might improve
detection in that electrical environment.
<br>
<br>

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. When
tracking is enabled the tracking filter is reset every time the
transmit WPM is adjusted.
<br>
<br>

CW detection is basically an amplitude demodulator. You can set
the threshold for detecting when the signal transitions from off-to-on
and on-to-off. These signal levels are relative to the average
signal level. The on-to-off is the "Lower" value and the
off-to-on the "Upper." This implementation provides a hysteresis
detector. Early fldigi CW decoders used this scheme but the
detection levels were not adjustable.
<br>
<br>

The RxWPM control is an indicator and is not used for setting the operation
of the CW decoder.
<br>
<br>

"SOM decoding" provides a fuzzy logic implementation to match the RX
stream detected on-off sequence to a "best fit" character. It can
increase the probability of correctly identifying the text character
under very noisy conditions.
<br>

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.
<br>
<br>

The transmit encoder settings for WPM can also be adjusted with three hot
keys:
<br>

<ul>
<li>Numeric keypad "+" increases the TxWPM by 1</li>
<li>Numeric keypad "-" decreases the TxWPM by 1</li>
<li>Numeric keypad "*" toggles between the selected TxWPM and a default WPM</li>
</ul>

The "Default" control on the CW tab sets that default value. As
shown above the TxWPM is 30 and the default is 18. If during a
QSO you needed to slow down to give the other op a better chance to
copy what you are sending, just hit the "*" on the numeric keypad and
the CW code will immediately switch to sending CW at the set default
value (18 wpm in this example). Press the "*" again to return to
back to the CW speed that you were previously using.<br>

\section subsec_timing Timing
<br>

\image html config-cw-qsk.png "Timing"
\image latex config-cw-qsk.png "Timing" width=5.0in
<br>
<br>

Fldigi generates CW by inserting a keyed tone at the current
waterfall audio frequency. The transceiver should be operated in
either USB (preferred) or LSB mode.
The CW signal is completely generated in the software so it is possible
to control many aspects of the CW signal. 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.

<ul>
<li>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.</li>

<li>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.</li>

<li>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.</li>

<li>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.</li>

<li>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.</li>

<li>The transmitted signal can be further wave shaped using a "Windowed-sinc"
bandpass filter.  It is enabled by checking the "BPF transmit audio" check box.
The bandwidth of the filter can be adjusted from 10 to 1000 Hertz with the BPF bw
control.  The filter will always be centered on the AFCW injection frequency
(waterfall TX cursor position).  You should both visually observe and listen to
the resulting CW signal.  The easiest way to do this is to enable the "Send continuously",
select a test character and then press the TX button on the main dialog.  The
weight, dash/dot, edge shape selection, edge timing, BPF and bandwidth can be
changed with immediate effect.</li>
</ul>

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.
<br>
<br>

\image html cw-00-30.png "Dash/Dot = 3.0, Edge = 0.0"
\image latex cw-00-30.png "Dash/Dot = 3.0, Edge = 0.0" width=2.8in
<br>
\image html cw-00-40.png "Dash/Dot = 4.0, Edge = 0.0"
\image latex cw-00-40.png "Dash/Dot = 4.0, Edge = 0.0" width=2.8in
<br>
\image html cw-30-30.png "Dash/Dot = 3.0, Edge = 3 msec"
\image latex cw-30-30.png "Dash/Dot = 3.0, Edge = 3 msec" width=2.8in
<br>
\image html cw-60-30.png "Dash/Dot = 3.0, Edge = 6 msec"
\image latex cw-60-30.png "Dash/Dot = 3.0, Edge = 6 msec" width=2.8in
<br>
\image html cw-120-30.png "Dash/Dot = 3.0, Edge = 12 msec"
\image latex cw-120-30.png "Dash/Dot = 3.0, Edge = 12 msec" width=2.8in
<br>

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.<br>
<br>

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)<br>
<br>

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.<br>
<br>

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.
<br>

\section subsec_qsk QSK
<br>

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.
<br>
<br>

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 theAFCW
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.<br>
<br>

The right audio channel QSK signal is selected by checking the box and
then adjusting the pre and post timing in millisecond increments.
Additional information and a schematic diagram of a QSK keying circuit
is described in \ref cw_keying_page "CW Keying". 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.
<br>
<br>

\section subsec_prosigns PROSIGNS

\image html config-cw-prosigns.png "CW Prosigns"
\image latex config-cw-prosigns.png "CW Prosigns" width=5.7in
<br>
\image html config-cw-prosign-popup.png "Prosign Popup"
\image latex config-cw-prosign-popup.png "Prosign Popup" width=1.0in

You can assign keyboard characters to be used for Morse prosigns. The
available characters are: ~ % &amp; + = { } &lt; &gt; [ ]
<br>
<br>

The default assignments are shown above. You can also elect to send and
receive the KN prosign as an open parenthesis '('. This is commonly
used on MARS CW operations.
<br>
<br>

See \ref cw_page "Operating CW" for additional information.
<br>
<br>

\ref cw_configuration_page "Return to Top of Page"
<br>
\ref main_page "Return to Main Page"


*/