sdrangel/plugins/channeltx/modam

AM modulator plugin

Introduction

This plugin can be used to generate a narrowband amplitude modulated signal. "Narrowband" means that the bandwidth can vary from 1 to 40 kHz.

Interface

The top and bottom bars of the channel window are described here

1: Frequency shift from center frequency of transmission

Use the wheels to adjust the frequency shift in Hz from the center frequency of transmission. Left click on a digit sets the cursor position at this digit. Right click on a digit sets all digits on the right to zero. This effectively floors value at the digit position. Wheels are moved with the mousewheel while pointing at the wheel or by selecting the wheel with the left mouse click and using the keyboard arrows. Pressing shift simultaneously moves digit by 5 and pressing control moves it by 2.

3: Channel power

Average total power in dB relative to a +/- 1.0 amplitude signal generated in the pass band.

4: Channel mute

Use this button to toggle mute for this channel.

5: RF bandwidth

This is the bandwidth in kHz of the channel signal filtered after modulation. It can be set continuously in 1 kHz steps from 1 to 40 kHz.

6: Modulation level

Adjusts the AM modulation level in %

7: Volume

This is the volume of the audio signal from 0.0 (mute) to 2.0 (maximum). It can be varied continuously in 0.1 steps using the dial button.

8: Level meter in %

• top bar (beige): average value
• bottom bar (brown): instantaneous peak value
• tip vertical bar (bright red): peak hold value

You should aim at keeping the peak value below 100% using the volume control

9: Input source control

9.1: Tone input select

Switches to the tone input. You must switch it off to make other inputs available.

9.2: Morse keyer input select

Switches to the Morse keyer input. You must switch it off to make other inputs available.

9.3: Tone frequency (kHz)

Adjusts the tone frequency from 0.1 to 2.5 kHz in 0.01 kHz steps

9.4: Audio input select and select audio input device

Left click to switch to the audio input. You must switch it off to make other inputs available.

Right click to select audio input device. See audio management documentation for details.

10: CW (Morse) text

Enter the text to be keyed when Morse input is active and in text mode

11: Clear CW text

Clears the CW (Morse) text

12a: Morse keyer controls (line 1)

12a.1: CW keying speed

Sets the CW speed in Words Per Minute (WPM). This is based on the word "PARIS" sent 5 times. For 5 WPM the dot length is 240 ms. In other terms the dot length is calculated as 1.2 / WPM seconds. The dot length is used as the base to compute other timings:

• Element (dot or dash) silence separator: 1 dot length
• Dash: 3 dot lengths
• Character silence separator: 3 dot lengths
• Word silence separator: 7 dot lengths

12a.2: Dots keying

Switch this button to send dots continuously

12a.3: Dashes keying

Switch this button to send dashes continuously

12a.4: Text keying

Switch this button to send the text typed into the text box (10)

12a.5: Text auto repeat

Switch this button to auto repeat the text keying

12a.6: Text play/stop

Use this button to stop sending text. When resuming keying restarts at the start of text

12a: Morse keyer controls (line 2)

⚠ WARNING: what follows is not really useful if you do not use a proper Morse keyer with direct audio feedback. There is a significant audio delay either with the direct monitoring or by monitoring the transmitted signal so keying with this audio as feedback is not practical

12b.1: Activate morse keys keyboard and mouse control

This disables text or continuous dots or dashes. Toggle input from keyboard or mouse (see 16b.3). Occasionally the focus may get lost and you will have to deactivate and reactivate it to recover the key bindings.

12b.2: Iambic or straight

Choose iambic or straight keying style. When straight is selected the dot or dash key may be used.

12b.3: Mouse control pad

When keyboard and mouse control is activated move the pointer to this area to use the left button as the dot paddle and the right button as the dash paddle. In straight mode both buttons have the same effect (key down).

12a.4: Register dot key

Click on the button and while selected type a character or character and modifier (Shift + key for example) to select which key is used for dots. The key or key sequence appears next (here dot .)

12a.5: Register dash key

Click on the button and while selected type a character or character and modifier (Shift + key for example) to select which key is used for dashes. The key or key sequence appears next (here minus sign -)

13: Audio file path

The path to the selected audio file to be played or dots if unselected

14: Audio file play controls

14.1: Audio file select

Opens a file dialog to select the audio file to be played. It must be mono 48 kHz F32LE raw format. Using sox a .wav file can be converted with this command: sox piano.wav -t raw -r 48k -c 1 -b 32 -L -e float piano.raw

14.2: Audio file loop

Audio replay file at the end

14.3: Play/pause file play

Toggle play/pause file play. When paused the slider below (17) can be used to randomly set the position in the file when re-starting.

15: Play file current position

This is the current audio file play position in time units relative to the start

16: Play file length

This is the audio file play length in time units

17: Play file position slider

This slider can be used to randomly set the current position in the file when file play is in pause state (button 14.3)