FreeDV sends speech as modem tones in an ordinary SSB channel. Radio Remote does the FreeDV work on the Pi, so you only need the browser:
Modes: RADE V1 (the neural mode most stations use today) and RADE V2 (see below). Both come from one optional library, the same one that has always held RADE. The older codec2 modes (1600, 700D, 700E) were removed from the program; a configuration file that still names one of them is read as RADE V1.
Status: the modem round trip (voice to tones to voice, noise rejected) is covered by automated tests. How well it works over the air with your radio, antenna and band has to be found out by trying it: start with receive, then transmit into a dummy load.
Switching FreeDV off passes the radio's audio through as before (it does not change the radio's mode back).
A FreeDV modem only locks when the signal is close to where it expects it, and a radio dial cannot be set that finely by hand. Measured with ideal signals: RADE V1 locks only within about ±50 Hz, so the Pi does the fine tuning in software (RADE V2 locked across the whole ±300 Hz tried, so for V2 the search is rarely needed):
FT-991A: use plain USB/LSB, like the other stations (recommended, and the default). Below 10 MHz FreeDV uses LSB, above it USB, with the same dial frequencies as the channel list and the FreeDV Reporter. Every station you meet is on its radio's ordinary SSB mode, and a DATA mode can put your signal somewhere else (see below). In USB/LSB the radio's filter is 2400 Hz, which carries RADE V1 (audio 750 to 2250 Hz) and V2 (about 1000 to 1900 Hz), and the radio's own SSB transmit filter (menu 110, for example 400-2600 Hz) trims the edges of the signal. What the radio must not do is process the audio:
| Menu / control | Value |
|---|---|
| Speech processor | OFF (also RF/AF compression, noise reduction, notch and contour on receive) |
| Parametric microphone equalizer (menus for the mic EQ) | OFF |
| 110 SSB TX BPF | at least 400-2600 Hz (100-2900 Hz is the widest of the usual choices) |
| 106 SSB MIC SELECT, 109 SSB PORT SELECT | REAR, USB (the page's microphone button sets 106) |
| 107 SSB OUT LEVEL | the receive level to the Pi: the tones clearly present, never clipping |
Set the transmit level with the Level test (see below): the radio's ALC must stay under its mark and the power should be close to what you set; a compressed RADE signal cannot be decoded.
Alternative: the radio's DATA mode (the way the FreeDV guide for the FT-991A does it). The DATA modes bypass the radio's microphone chain, but they have traps of their own: the receive filter starts at 500 Hz (see the filter width below), the transmit band is not trimmed by menu 110, and the OTHER DISP / OTHER SHIFT menus (064, 065) change the relation between the displayed frequency and the carrier, so at the same displayed frequency your signal may sit up to 1500 Hz away from where a USB/LSB station expects it (V1 only locks within about 50 Hz: nothing would decode). Use it only if you have checked all three. FreeDV's own guide sets these menus once on the radio:
| Menu | Name | Value |
|---|---|---|
| 031 | CAT RATE | 38400 |
| 059 | CW FREQ DISPLAY | DIRECT FREQ |
| 062 | DATA MODE | OTHERS |
| 064, 065 | OTHER DISP (SSB), OTHER SHIFT (SSB) | 1500 Hz |
| 066, 068 | DATA LCUT FREQ, DATA HCUT FREQ | OFF |
| 070 | DATA IN SELECT | REAR (the page's microphone button sets it) |
| 071 | DATA PTT SELECT | DAKY |
| 072 | DATA PORT SELECT | USB |
Then switch on Use the radio's DATA-USB / DATA-LSB mode in the FreeDV tab (administrators): FreeDV then puts the radio in DATA-USB (DATA-LSB below 10 MHz) instead of USB (LSB). It is off by default because it needs the menus above. The receive level that goes to the Pi is then menu 073 DATA OUT LEVEL (in USB/LSB it is 107 SSB OUT LEVEL).
The radio's filter width: RADE V1 needs about 1500 Hz of the audio, and the DATA modes start too narrow (BENCH-FOUND). RADE V1 occupies about 1500 Hz: the audio from about 750 to 2250 Hz (V2 about 900 Hz, around 1000 to 1900 Hz). An FT-991A in a DATA mode starts with a 500 Hz receive filter (width code 10 in the radio's table): a recording of the noise in DATA-L spanned exactly 1225 to 1750 Hz, and the reference RADE decoder found nothing in it, because only a third of the carriers get through. The DATA filter is centred on 1500 Hz, so 1700 Hz is the least that carries V1 and about 2000 Hz is comfortable; in USB/LSB the passband starts near 300 Hz, so about 2100 Hz is needed and the default 2400 Hz is fine. More than that only lets in more noise and neighbouring stations (it does not help RADE). The width is kept per mode (USB and DATA-L have their own), and the DATA modes have no width key on the radio's front panel, so the Filters tab shows a Width list for DATA-U and DATA-L as well, and the FreeDV tab shows a warning with a Widen button when the filter is too narrow while FreeDV is on. With Open the radio's filter automatically ticked (the default; administrators can change it), the app opens a too-narrow filter by itself a moment after FreeDV is switched on or the mode changes, to the narrowest value from 2000 Hz (DATA) or 2400 Hz (USB/LSB) up. Check it with a recording of the noise (REC on the Radio tab, then Download raw radio audio): it should span roughly 750 to 2250 Hz or more.
Always: speech processor off, no equaliser tricks (the radio must pass the modem tones unchanged).
RADE V1 sends speech as an OFDM signal that is about 2.1 kHz wide and decodes at lower signal-to-noise ratios than 700D/700E (it still locks at about 0 dB on a fading path). It is the mode most FreeDV activity uses. It comes from a separate library of about 24 MB.
A new installation already has it, you do not need to do anything: the ready-made image and the installer pack contain the RADE library, and install.sh (Raspberry Pi or
Debian PC) downloads and installs it as part of the install (--no-rade skips it). Ordinary updates do not carry it, so they stay small, and a library that is already installed is kept.
If it is missing, for example because the install had no internet: an administrator presses Install RADE in Admin > Config > RADE (or in the FreeDV tab, which shows the same
button; once RADE is installed it says Reinstall RADE). The Pi downloads the library from the project's release page, checks its SHA-256, puts it in /var/lib/radio-remote/lib and starts
using it at once, with no restart. It works on 64-bit Linux: a Raspberry Pi with the 64-bit OS, or Debian 12/13 on a 64-bit PC (see installation, route D). The library is built on
Debian 12 and runs on Debian 12 and newer. From the command line:
sudo /opt/radio-remote/current/scripts/install_rade.sh # downloads the matching release file, checks its SHA-256, installs it, restarts the service
sudo /opt/radio-remote/current/scripts/install_rade.sh --file F.tar.xz # from a file you copied to the Pi (no internet)
sudo /opt/radio-remote/current/scripts/install_rade.sh --remove
Then choose RADE in the mode list of the FreeDV tab (or in a channel). Until it is installed the tab says so and offers only the codec2 modes.
rade_c C port (BSD licence, with the Opus sources it uses); the release includes the licence files.
It runs in the same program as the rest of the server (about 3% of one fast PC core to decode, less to encode; expect roughly a quarter to a
third of one Pi 4 core while receiving: not yet measured on your Pi).At the end of every RADE V1 transmission the Pi sends your callsign inside the signal (in the end-of-over frame), the way the FreeDV program does, so other stations' programs can show who was calling.
/. Left empty, the Callsign of the Reporter settings is used
(its first 8 characters). The configuration key is [freedv] callsign.Choose RADE V2 in the mode list. It is a newer version of the same idea with a narrower signal (about 1.1 to 1.9 kHz), its own level control on receive, and it follows a mistuned signal by itself. A V1 station cannot decode a V2 station and the other way round, so use the version the other station uses; most stations are on V1 today.
RADEV2 (as other open-source clients report it).First check that you and the other station use the same RADE version. V1 and V2 are different waveforms and do not decode each other at all (the reference decoder gave 0 % lock on a V2 recording with V1 and the other way round). Many stations on the air use V2 now (about 900 Hz wide, around 1000 to 1900 Hz of the audio) while others use V1 (about 1500 Hz, 750 to 2250 Hz). Ask the station, look at the mode on the FreeDV Reporter list, and set the same one on the FreeDV tab; a station that "cannot understand anything" is very often on the other version.
Check that the transmitted signal stays in its band. The V1 modem's output is made of OFDM carriers with sharp edges; without a band-pass filter about 7 % of its power falls outside 700 to 2300 Hz (skirts down to the audio floor and up past 3 kHz), so on someone's waterfall it looks wider than it should and the radio's ALC and filters see it. RADE V2 has its filter on by default; for V1 the library has it but leaves it off. Libraries installed from 1.1.30 on have it switched on (1.6 % outside the band, a lower peak-to-average ratio): if the FreeDV tab says the installed RADE library is older, press Reinstall RADE.
RADE needs a continuous stream of tones, with no holes in it. The Pi therefore keeps a small cushion (about 0.2 s) of modem tones queued before it starts sending them to the radio, so an uneven network (Wi-Fi, a remote connection) cannot put gaps into the signal; when you release PTT the Pi first sends the last modem frame (silence completes it) and lets the queued tones reach the radio, so the end of the over is not cut off; the radio is unkeyed about half a second after you let go. After every over the service log says whether the tones went out whole:
journalctl -u radio-remote --since "10 min ago" | grep "FreeDV transmit"
no holes is good. the tones had N hole(s) means the audio reached the server unevenly or the PC is too slow: use a wired connection, close other programs, and send the line to the developers.
Admin > Diagnostics (and /api/diagnostics) also shows the slowest processing step, which should stay well under 20 ms on the receive side. A PC that regularly needs longer than that for one 20 ms frame will stutter.
qso.freedv.org is the live list of FreeDV stations: callsign, grid square, frequency, mode, whether the station is transmitting right now, and a short message. Radio Remote can join it. It is off by default.
IO91wm) to be listed, plus an optional short message. Choose whether to announce this station, to show who is on the air, or both. Apply.[reporter] (enabled, announce, watch, callsign, grid_square, message).The list on the FreeDV tab comes from the configuration (freedv.channels). The defaults are the usual FreeDV calling frequencies (160 m
1.997, 80 m 3.625 and 3.643, 40 m 7.177 and 7.197, 20 m 14.236 and 14.240, 17 m 18.118, 15 m 21.313, 12 m 24.933, 10 m 28.330 and 28.720 MHz, all in kHz
as dial frequencies). Check the current activity frequencies on the FreeDV website before relying on them.
Administrators can change the list in the tab (Edit the channel list): name, frequency in MHz, mode.
Settings (Admin > Config or the tab): freedv.mode (the mode used when FreeDV is switched on without choosing one), freedv.tx_level_db (-40..+3), freedv.channels.
RADE's transmit signal has an almost constant amplitude (the paper reports a peak-to-average ratio under 1 dB before the radio). It is meant to be sent at close to the radio's full rated power, and "more is not better" only applies beyond that: an overdriven signal is distorted and decodes badly, but an underdriven one is simply weak at the other station. A radio whose ALC barely moves (one or two bars at every setting) is underdriven.
A measured example (FT-991A in DATA-USB, set to 50 W, an external power meter, the test tone): -6 dB gave 32 W and the ALC barely moved; 0 dB gave 41 W with the ALC just below its limit; +3 dB gave 42 W with the ALC at its limit. So 0 dB was the right level for that radio: the last 3 dB bought 1 W and started the overdrive. The default for a new installation is -3 dB, a safe starting point; every radio and cable is different, so run the level test. Read the external meter if you have one: the app's PO bar saturates at the set power.
The level can go up to +3 dB. If the ALC is still not moving at +3 dB, raise the radio's own input level for the USB audio instead (on an FT-991A the sound-card playback volume on the computer, or the radio's DATA/USB input gain menus) rather than turning up the level beyond that.
Small PCs (an Intel Atom mini PC, for example): RADE V1 receive needs about 40% of one core and the decoder has single steps of 60 to 100 ms. Such a PC also changes its CPU clock all the time (down to 480 MHz when it looks idle), and RADE's short bursts of work then run slowly. Keep the clock up with the "performance" governor, permanently:
sudo tee /etc/systemd/system/radio-remote-cpu-performance.service >/dev/null <<'EOF'
[Unit]
Description=Radio Remote: CPU governor performance
After=sysinit.target
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/sh -c "for g in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do echo performance > $g; done"
[Install]
WantedBy=multi-user.target
EOF
sudo systemctl daemon-reload && sudo systemctl enable --now radio-remote-cpu-performance.service
(undo: sudo systemctl disable --now radio-remote-cpu-performance.service). On the Atom tested the clock still swung between 1.0 and 1.9 GHz (its power limit), but the worst decoder step fell from 107 to 68 ms.
RADE V2 is lighter for the decoder on such a PC (about 30% of a core, worst step 19 ms). Admin > Diagnostics shows the receive timing: the time per 20 ms frame in total and the time inside the decoder; the total must stay under 20 ms on average.
python3 scripts/freedv_probe.py (on the Pi: /opt/radio-remote/venv/bin/python /opt/radio-remote/current/scripts/freedv_probe.py) runs every installed mode as a
transmit-to-receive loopback and prints the share of one CPU core each needs and its slowest single step. On a PC RADE needs about 1% to transmit and 5% to receive; on a small Intel Atom PC receive was measured at about 40% of one core.
| Symptom | Likely cause |
|---|---|
| The FreeDV tab offers no mode | the RADE library is not installed (Admin > Config > RADE > Install RADE) |
| Status stays at "no signal locked yet" | wrong frequency or sideband, signal too weak, RX level too low or clipping, or it is another mode (RADE V1 and V2 signals do not decode as each other) |
| "Tap the speaker icon" | the Pi only decodes while someone is listening |
| Locks, but the speech is garbled | an overloaded receive level (lower menu 107) or a very weak signal |
| Others cannot decode you | overdriven or too-weak transmit level, speech processor on, or the radio not in USB/LSB |