Fldigi Setup Guide: Sound Card, Rig Control and Macros

FT8 may dominate the waterfall today, but a huge range of keyboard digital modes is still alive on the bands: PSK31, RTTY, Olivia, MFSK, Contestia, Thor and many more. For most operators the gateway to all of them is fldigi, the free, open-source multimode program originally written by Dave Freese, W1HKJ. A good fldigi setup lets you move between these modes from one window, with rig control, macros and logging built in. A poor one produces splattered signals, frustrating PTT problems and decodes that never quite appear.

This guide walks through the setup step by step: the sound card and audio levels, rig control with flrig or Hamlib, PTT options, the waterfall, macros that save typing, and logging. Menus and options change between releases, so treat the descriptions here as a map and check the current fldigi documentation for exact wording.

What Fldigi Is and Why It Is Still Worth Learning

Fldigi is a sound-card digital modem. It turns received audio from your radio into text on the screen, and turns the text you type into audio for the radio to transmit. Unlike WSJT-X, which focuses on structured, timed weak-signal exchanges, fldigi supports free-form keyboard conversations. You can chat, send longer messages and run nets.

The wider suite

Fldigi is part of a family of programs from the same developers. flrig handles rig control, while other companion programs handle structured messages and file transfers. Many emergency communication groups use this suite because it works over radio without internet access. Even if you never use the companions, knowing they exist helps you understand some of fldigi’s menus.

Modes at a glance

If you are not sure which modes to try, our comparison of digital modes beyond FT8 explains how PSK31, RTTY and others differ. Fldigi supports all of them and more.

Before You Start: The Hardware Chain

Fldigi needs three connections between the computer and the radio:

1. Receive audio from the radio into the computer.
2. Transmit audio from the computer into the radio.
3. PTT and rig control, so the computer can key the transmitter and, optionally, read and set the frequency.

Many modern transceivers include a built-in USB sound card and a virtual serial port for CAT control over a single USB cable. Older radios use an external interface with its own sound card and a keying circuit. Either works well. If you already run FT8, the same hardware connections serve fldigi; our WSJT-X setup guide covers the audio chain in detail.

Step 1: Operator Details and First Run

On first launch, fldigi typically offers a configuration wizard. It asks for your callsign, name, locator and other operator details, which are used in macros and the log. Fill them in carefully; macros insert this information into your transmissions, and a typo will be repeated in every contact.

Next, the wizard moves to the sound card, rig control and PTT sections. You can return to all of these later through the configuration menu, so do not worry if something is not right the first time.

Step 2: Sound Card Configuration

In the audio section, choose the sound device for capture (receive) and playback (transmit). With a radio’s built-in USB audio, the device usually appears with a name that identifies the codec or the radio. With multiple sound devices on the computer, choose deliberately and write down which is which. A classic mistake is to transmit through the computer’s speakers while wondering why the radio stays silent.

Sample rates

Fldigi lets you set sample rates and offers correction for sound cards whose clocks are slightly off. For most keyboard modes, the defaults are fine. Some precise modes are more sensitive to sound card timing, and the documentation explains how to measure and correct it if necessary.

Receive level

Set the receive audio so the band noise appears as a moderate level on the waterfall and the signal level indicator, not flat and not saturated. Too little audio hides weak signals in quantisation noise; too much overloads the sound card and creates false traces. Adjust the radio’s USB audio output level or the computer’s recording level until the noise floor sits comfortably in the middle of the range.

Step 3: Transmit Audio and Clean Signals

Transmit audio level is the setting that most affects other operators. Overdriving the transmitter creates a wide, distorted signal with sidebands that interfere with nearby stations, which is particularly harmful on narrow modes like PSK31.

Setting the level

• Start with the transmit audio low on both computer and radio.
• Transmit into a dummy load or on a clear frequency and raise the level slowly.
• Watch the radio’s ALC indicator. Aim for little or no ALC action; set the power with the radio’s power control, not by pushing audio harder.
• Remember that modes with constant amplitude and modes with varying amplitude load the transmitter differently, so check levels when you change mode families.

Check your signal

Ask another operator for a report, or look at your signal on a web SDR receiver. A clean PSK31 signal shows two distinct traces with nothing else around them. Extra traces or a smeared signal mean the audio is too high or something in the chain is distorting.

Step 4: Rig Control Options

Rig control lets fldigi read your frequency for the log and waterfall scale, change frequency and mode, and in many cases key PTT through CAT commands. Fldigi offers several ways to do this.

flrig or Hamlib?

Both work well. flrig gives you a dedicated control panel and lets several programs share one radio through its network interface. Hamlib is a good choice if other programs in your station already rely on it. If you use Hamlib elsewhere, our guide to rig control with Hamlib explains serial ports, baud rates and the network daemon approach. The main rule is to choose one path and avoid two programs trying to open the same serial port directly.

Step 5: PTT

PTT can be triggered in several ways: a CAT command, the RTS or DTR line on a serial port, a GPIO on some USB sound interfaces, or VOX in the radio. CAT PTT through flrig or Hamlib is often the neatest when available. Serial RTS or DTR is reliable with interfaces designed for it. VOX works but can clip the start of transmissions and trigger on system sounds, so disable computer notification sounds on the transmit audio device if you use it.

Test PTT before you go on the air: the radio should switch to transmit when fldigi transmits and switch back cleanly when it stops, without hanging in transmit.

Step 6: The Waterfall and Tuning

The waterfall is where you find and tune signals. Click on a signal to place the receive cursor on it, and fldigi decodes it. Automatic frequency control (AFC) can keep the cursor locked on a drifting signal, and a squelch setting suppresses random characters from noise.

Useful waterfall habits

• Set the waterfall so the noise floor is dark and signals stand out clearly.
• Use the signal browser or multi-channel view for PSK to see several conversations at once.
• Keep your transmit signal near the centre of the radio’s passband to avoid the filter edges.
• Mode identification features and reverse sidebands help when a signal does not decode as expected, particularly for RTTY.

Step 7: Macros That Save Typing

Fldigi macros are pre-written transmissions attached to function keys and buttons. They use tags that fldigi replaces with real values: your callsign, the other station’s callsign, the signal report, the time and so on. Tags also control the transmitter, for example starting transmission at the beginning of a macro and returning to receive at the end.

Macros worth setting up

• CQ: a short call repeated a few times, ending with a return to receive.
• Answer: the other station’s call, your call, and a return to receive.
• Exchange: signal report, name and locator.
• Station details: a short description of your radio and antenna for longer chats.
• Sign-off: thanks, 73, and a final return to receive, often combined with logging the contact.

Keep macros short. Long “brag files” about station equipment waste time on shared frequencies and are often ignored. For contests, fldigi offers contest-oriented features and exchange fields, and macros can insert serial numbers automatically.

Step 8: Logging

Fldigi includes a built-in logbook that records contacts with fields filled from the QSO entry area. It can export in ADIF for import into your main logging program or for uploading to confirmation services. Many operators prefer to keep one master log elsewhere and use fldigi’s connection features or exports to feed it. Whatever you choose, make sure contacts end up in your main log with the correct mode and frequency.

Operating Etiquette on Keyboard Modes

Keyboard modes are conversational, and a few habits make you a welcome presence on the band.

Listen before you transmit

Watch the waterfall for a while before calling. A quiet area of the waterfall may be quiet because a weak station is there, and on narrow modes several conversations can share a small slice of spectrum. Leave space between your signal and others, and check your national band plan for the segments where each mode is expected.

Keep overs short and clear

Typed contacts are slower than voice. Short overs keep the conversation moving and are more robust when conditions fade. End each over with a clear handover, such as the other station’s callsign followed by your own and a return to receive, so the other operator knows it is their turn.

Choose the mode for the conditions

If a PSK31 contact keeps breaking up, suggest moving to a more robust mode such as Olivia or MFSK. Fldigi makes switching easy, and both stations change mode from the same menu. Agree the new mode and frequency before switching so you do not lose each other.

Troubleshooting Common Fldigi Problems

• Nothing on the waterfall: wrong capture device or muted recording level.
• Radio does not transmit: PTT method misconfigured, wrong serial port, or another program holding the port.
• Transmits but no power: wrong playback device, audio too low, or the radio’s data input not selected.
• Wide, splattered signal: transmit audio too high and ALC active.
• Frequency display wrong: rig control not connected or the mode offset incorrect.
• Garbled RTTY: reversed shift or mismatched baud rate; try the reverse option.

The Bottom Line

A solid fldigi setup comes down to a handful of careful steps: choose the right sound devices, set receive and transmit levels for clean signals, connect rig control through flrig or Hamlib without port conflicts, test PTT, learn the waterfall and write a few short macros. Once it is working, fldigi opens the door to dozens of keyboard modes from one program. It rewards the effort with real conversations on the bands, something structured weak-signal modes rarely offer.

Frequently Asked Questions

Is fldigi free?

Yes. Fldigi is free, open-source software available for Windows, macOS and Linux, and the source code is published on SourceForge.

Should I use flrig or Hamlib with fldigi?

Both work. Flrig offers a dedicated control panel and easy sharing with other programs, while Hamlib suits stations that already use it elsewhere. Avoid two programs opening the same serial port directly.

How do I set transmit audio levels in fldigi?

Start low, transmit into a dummy load or a clear frequency and raise the level until you reach the desired power with little or no ALC. Set power with the radio’s power control.

What are fldigi macros?

Macros are pre-written transmissions on function keys. Tags insert details such as callsigns and reports automatically and control when the transmitter starts and stops.

Can fldigi and WSJT-X share the same radio?

Yes, if they use the same sound device and rig control path without conflicts. Run one at a time or share control through flrig or a Hamlib network daemon.

Why does my PSK31 signal look wide?

Usually because the transmit audio is too high and the transmitter is being overdriven. Reduce the audio until ALC action stops.