Using Fldigi

  1. Using Fldigi For Cw
  2. Decoding Cw Using Fldigi
  3. Using Dl-fldigi
  4. Using Fldigi To Send And Receive Morse Code
  5. Using Fldigi With N1mm

To start fldigi: /usr/bin/fldigi. Or, click on the fldigi icon in Launcher on the desktop. Configuring Fldigi. On the first startup, a configuration wizard opens. You can also complete this process using the fldigi Configuration Menu. Detailed instructions are in the User Manual. Here are some settings for fldigi with a MicroHam USB Interface III. The Fldigi package can be quite capable for low-power operations. I have run contests using Fldigi on the RasPi 3, while portable in a state park, and it is a very rewarding experience to be able to do digital modes without a full-sized computer. FLdigi ('Free Light Digital Modes) is a free open-source computer program that uses a computer sound system as a DSP modem to send and receive text and computer data over two-way radios. It can generate a large variety of transmission modes that trade off various combinations of transmission speed, occupied bandwidth on. FLDIGI will be sending tones to our radio for transmission, receiving tones from our receivers for display on our computer screen, and commanding our radios to go from receive to transmit when we send data.


Finally got FLDIGI working completely over USB with FLRIG on WIN 10 PC with ICOM 7300 - Here's How....


I finally got FLDIGI working completely, modulating the ICOM 7300 signal and controlling it using a single USB cable with FLRIG. On a Win 10 PC 64 bit, with the latest Win 10 update.
Thank you guys (all the guys from this group that gave lots of this information in my earlier post) and I hope this makes a complete listing of what you have to do for any new hams (like me) or anyone else that wants to get their 7300 set up for digital mode operation (receive AND send):
Before all the settings are listed below, let me give a brief explanation of how this connection works, for anyone interested, especially any new hams, because it's very complicated and not completely self evident from the titles and abbreviations of all the settings....Some of you know this....I didn't! I may be missing a few things here, but this is my dissertation at this time...I hope others will add to it or correct it as needed.
The 7300 lets you switch to transmit mode and also modulate its transmitted signal either through the mic or the accessory port or the USB port. When you load the driver from ICOM into your PC, it enables communication between the 7300 and your PC over the USB cable, assigning one of the PC ports to it. You can check this and see if it is really installed by going to the device manager of your pc, checking under ports, and looking to see if a silicon labs driver is there, assigned probably to COM 3. If you don't see that, your 7300 is not connected to your PC. You need to get that working first before anything happens.
In FLDIGI you need to set the soundcard for both Capture and Playback to USB audio Codec, which is the connection to the 7300 and not your soundcard in your PC. (I didn't have the PLAYBACK set to the USB audio codec, so while I heard the transmitted signal from FLDIGI over my PC speakers, it was not going into the USB cable and modulating the 7300). This was driving me crazy and I finally saw this error, and it corrected it and I finally had a modulated signal being transmitted!
On the 7300, when you select SSB-D (data mode) this makes the 7300 modulated by the signal over the USB cable and not the mic or key, as well as keying the transmission on. So you need Data mode on for this.
Now, concerning FLRIG: I think there is a bug that stops it from recognizing the COM3 selection when you start it. You need to see the COM3 in the Transceiver setup as you configure it to control the 7300. I had to mess with it a few times, turning it on and off, hitting UPDATE, hitting INIT (Initialize) until it finally saw it and connected to the 7300 and did initialize. Then it didn't appear the next time I started FLDIGI and FLRIG, but if you continue to mess with it, it does appear and you can connect again. I saved the configuration in settings but I'm not sure it will work again without messing around. I suspect a bug.
When FLRIG is working properly, you WILL actually see the 7300 frequency you are on appear on the FLDIGI screen, and you will have control of the 7300, as well as being able to decode signals and also send form your text entry box.
Here is a way to make sure you are actually modulating, not just can watch the ammeter on your power supply modulate with the signals if you are sending CW, but if you go to the Audio Scope screen on the 7300 and start transmitting for instance a MFSK16 message, you will see the complex waveform being generated on the little waterfall display on the left. It's really cool. You do see it as the individual digital bits on the FLDIGI waterfall.
Here are the 7300 settings sent to me earlier by others. I copied them and put SET because I matched them. The only difference is I am using 9600 baud instead of 19200. I can change it eventually...I'm just happy to be working now!!!

Select Menu / Set / Connectors
ACC/USB Output Select = AF That's what we want to decode SET
ACC/USB AF Output Level = 50% Avoid overload of fldigi's SET
audio processor
ACC/USB AF SQL = OFF (Open) Keep squelch open, let fldigi SET
do the job
ACC/USB AF Beep/Speech... Output = OFF Keep USB Audio controller free SET
of keyboard confirmation beeps.
What the hell should fldigi do
with that strange noise?
ACC/USB IF Output Level = 50% In this case we really don't care SET
ACC MOD Level = 50% We really don't care too
USB MOD Level = 50% That's what we want to send. SET
Use 50% input and output MOD
level to avoid overload of fldigi's
DSP and the IC-7300's finals.
DATA OFF MOD = MIC Keep ACC on for debugging purposes SET
... just in case :-)
DATA MOD = USB Use internal soundcard only! SET
EXTERNAL KEYPAD This parms are not related to SET
fldigi ... just to avoid confusion :-) ALL SET
CI-V Output (for ANT) = OFF Just set this parameter SET
CI-V USB Port = Unlink from [Remote] Make USB Port available SET
CI-V USB Baud Rate = 9600 Fixed communication speed, SET to 9600
may be increased ... this may
require H/W flow control mimics
CI-V USB Echo Back = ON This is what we expect to ensure SET
a command has been transferred properly
USB Serial Function = CI-V Make USB Port available for SET
serial CI-V-Commands
RTTY Decode Baud Rate = 9600 We really don't care ... SET
keep default or any other value
USB Send = OFF Do NOT use DTR or RTS unless you SET
have very good reasons!
USB Keying (CW) = OFF Do NOT use DTR or RTS unless you SET
have very good reasons!
USB Keying (RTTY) = OFF Do NOT use DTR or RTS unless you SET
have very good reasons!
Com3 is the Silicon Labs CP210x USB to UART Bridge.

Also, be sure you are using the USB Audio CODEC for your Icom for the Capture and Playback. The radio mode should be USB-D and Fldigi should be PKTUSB.
NOTE: It was suggested I try using Hamlib as the 7300 control program instead of FLRIG, but it will not load properly in the latest version of Win 10.
I Hope this acts as a guide for others trying to get this working. It's pretty complicated, but very cool once you get it going.
On to the other features of FLDIGI now to learn....
Mike Paitchell
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This modem is able to receive and transmit HF-Fax images, traditionally used for weather reports.

More technical information is available on the wikipedia article Radiofax.

Two modes are implemented IOC=576 or 288. The focus is made on black-and-white images, color mode is still experimental.

Many frequencies are available at for example.

When entering any Wefax mode, the reception window opens, and optionally the transmit window. it is always possible to bypass this with the menu bar:

As for any modem, weather fax has its own tab in the configuration window.

Embedded vs floating display mode

There are two display modes for this modem:

Using Fldigi
  • Embedded mode: This is the default mode, the normal receipt and transmit windows gets graphic (Like Hellschreiber mode).
  • Floating mode: There are two separate windows for transmission and reception. This was the only available mode until fldigi 3.21.49.

Hide transmission window.

This option, allows to closed by default, the transmission window, when entering Wefax mode. In embedded mode, this means that the entire window is used for reception (Most common mode). In floating mode, this implies that the transmission window is not opened by default.However, it is always possible to manually open or close the transmission window at any time.

Logging messages to ADIF file

Using Fldigi For Cw

Each time an image is saved, it is possible to log this event, with the frequency and reception time, to the Adif file. This option is disabled by default.

Frequency shift adjustment

The default frequency is 800 Hz. However, it is possible to adjust for example to 850 Hz for Deutsche Wetter Dienst.

Maximum rows number

It non-continuous (Non non-stop) reception mode, an image is automatically saved when it has more than this number of lines (Default 2500 lines). Once this number of rows is reached, the image is saved and a new image is read with the same parameters. This feature has two applications:

  • In automatic mode (APT control), if an image end is not detected, we can guarantee that the result will take no more than, for example, the size of two faxes. Typical faxes have about 1300 lines, so the max lines parameters can be tuned to, for example, 200 lines.
  • In manual mode, where images are read continuously, this cuts the received images into chunks of equal size.

Destination directory for saved images

Received images are saved in the default folder

$HOME/.fldigi/images (Linux) or <defaultpath>/fldigi.files/images


Additionally, they can be saved manually, at any time, using the button 'Save'. The PNG images received some extra text comments which can be displayed, for example, with GIMP.

Monochrome images

Fax images are monochromes and are saved as such by default. However, it is possible to bypass this parameter and save them as color RGB images.

To open the transmit window, you must of course select one of the two Wefax modems, and then right-click on the transmit (blue) window:

Then, the transmit window just opens. This is the same logic as sending MFSK images.

Then, you must open an image file using the button 'Load'. The image is then displayed, for example like that:

Now, to start the transmission, you just need to click 'Tx B/W' for black-and-white images, etc... During transmission, image reception is paused. The window will display each image line as it is sent. Please be patient, this may take a while. You might note that FlDigi status line displays the estimation transmit time, and the current stage (Start, phasing etc...); Color transmission ('Tx Color') is intentionally disabled at the moment.

To enter reception mode, one can click the 'View' menu tab, and select 'Weather Fax Image'.

At this time, the reception window opens. A big blank picture is visible, this is where the received image will be displayed. Several controls are available:

  • Save: This allows to save the current image as a PNG file at any moment.
  • Non-stop: At startup, the modem goes into automatic mode, and the text 'Abort' is displayed. When clicking 'Abort', this blanks the image and resets the APT detection. When 'Manual mode' is clicked, no APT detection is done. The Automatic/Manual mode is displayed in the reception window label.
  • Pause/Resume: At any moment, the image reception can be paused and resumed (State is displayed in the reception window label).
  • Zoom: This allows to zoom in/out the image.
  • FIR: This allows to select an input FIR (Finite Impulse Response) filter. Practically, the narrow filter (Default value) gives the best results. The selected value is saved in the configuration file.
  • Skip APT/Skip phasing: When in automatic mode, this allows to skip detection steps. This is often necessary when the signal is not very good.

When receiving an image, either in manual or automatic mode (APT control), other controls are displayed:

  • Line: The number of the line currently received.
  • Width: The image width in pixels. This is usually 1809, if LPM is 120.
  • LPM: Lines per minute: Typically 120, can be 60, 90, 120 or 240. This is detected in automatic mode, but can be manually adjusted.
  • Slant: This is used to adjust the slant of the image due to a clock inaccuracy. This value is saved in the configuration file, so it is not needed to reenter it each time.
  • Center: This is used to manually adjust the horizontal center of the image, if it could not be detected in the phasing step.
  • Auto: When this button is set, the image will be automatically centered. This process starts after some hundredth of lines are received, by shifting left and right the image. It takes some time to converge.


APT control reception mode

This mode uses the APT start and STOP frequencies to detect the beginning and end of an image. Additionally, it tries to detect the phasing signal - a wide black band - to detect the center of the image. This method is helped by the estimation of the signal power of these frequencies.

Decoding Cw Using Fldigi

Manual reception mode (Non-Stop)

In this mode, the image is continuously read and displayed. When the maximum number of lines is reached, the image is saved and blanked, and the line counter returns to one.

Input FIR filters

There are three input Finite Impulse Response filters available. Here are their frequency characteristics:

Narrow filter, the default one, give the better results.

Centering an image

If the phasing was not automatically detected, the modem could not deduce the beginning of an image. The result is an image which is horizontally shifted. To correct this, one can use the 'Center' slider.

Picture with a slant

If either the send, receive or both ends of the transmission are using an uncalibrated sound card whose sampling rate is not an exact multiple of the sample rate the resulting picture at the receive end will appear slanted. The degree of slant is directly related to the accumulation of the frequency error at both ends of the transfer. Stations wishing to receive Weather fax pictures should calibrate their sound card.

The WWV calibration mode is used to measure and set the parts per million (ppm) correction factor for the sound card.

Your sound system may be fully corrected, but the sending station may have an uncorrected sound card. You can usually correct for small errors during reception by using the slant slider. Its value (Typically between - 0.005 and 0.005) will be stored in fldigi configuration parameters.

Automatic centering.

If the phasing signal could not be used for centering the image, the program waits for a string image signal anyway to go into reception mode, but it sets an internal flag allowing to automatically center the image. This feature can be freely enabled and disabled at any moment. it works by detecting a wide vertical band of about hundred pixels, where the sum of the contrast as the lowest among the complete image width.


That is: It computes for each row and each pixel, the absolute value of the horizontal derivate. It then sums these derivatives pixel-wise, row by row. Then, it computes an average of about hundred pixels along this single row. The column which has the lowest averaged contrast is considered to be the image margin, which is then shifted on the left of the window.

This method takes some time to stabilize, because at the beginning, there are many areas of the image, without details. It gets stable at the end, when only the margin stays with few contrasted details.

Image detection based on signal power

The APT control - inherited from the Hamfax signal, does not work very well when the image is noised. On the other hand, fldigi provides ways to evaluate the signal power on a given bandwith. This is used because APT control relies on the emission on specific frequencies.

Therefore, in the APT start and phasing loops, when check for the presence of strong signals associated to APT control. This information is used to take a decision when the traditionally method does not detect anything.

These two methods are interchangeable but used together for better detection.

AFC: Automatic Frequency Control

Using Dl-fldigi

This option controls the frequency on the complete spectrum width. After several hunderads of lines have been correctly loaded (That is, with a high line-to-line correlation), the AFC locks until the frequency or mode is manually changed.

Noise elimination

This option eliminates short-lived noise, individual pixels with a different value from their horizontal neighbors. They are modified using median values. This is based on the fact that no line should be narrower than two pixels, otherwise such an image would not be broadcast, because not correctly readable. It is therefore impossible to have one single pixel, simultaneously very different from its left and right neighbors.

Binary images

Faxes can be stored as binary or grey level images. The cutoff level between black and white (Default 128) can be adjusted. No information is lost until the image is saved, therefore this level can be freely modified until image end. The purpose of this option is to save disk space.

Using Fldigi To Send And Receive Morse Code

Displaying received files

Using Fldigi With N1mm

Each time the end of an image is detected, an image file is created and its name appears on the file list of the reception window. By clicking on a file name, it is displayed in the transmit window.

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