FLdigi, FLrig, and the sound-card suite

The FL suite (maintained by W1HKJ and contributors) covers sound-card digital modes: PSK31, RTTY, Olivia, MT-63, and more. FLrig provides CAT rig control shared with FLdigi; FLmsg handles formatted messages (NBEMS-style traffic — separate from casual POTA).

Manual: Fldigi help — rig control

When FLdigi still matters

FT8 dominates weak-signal hunting, but PSK31 and RTTY remain valid POTA modes — especially for activators who want variety after the minimum QSO count. Each distinct mode on the same band can count as a separate QSO toward POTA minimums (same hunter, same UTC day). Confirm current rules on docs.pota.app.

FLdigi fits when:

You already know PSK31 pileup rhythm.
Your radio lacks native WSJT-X integration but has USB audio.
You want lower duty cycle than FT8 for battery-powered summits.

Field architecture

Radio (USB audio + CAT) ←→ FLrig (optional) ←→ FLdigi ←→ headphones
                              ↑
                         WSJT-X can also use FLrig as rig

Recommended path: install FLrig and enable in FLdigi → Configure → Rig control → Enable flrig xcvr control with fldigi as client. Default host 127.0.0.1, port 12345. FLrig then handles frequency, mode (USB-D), and PTT; FLdigi handles modem encode/decode.

WSJT-X can select FLrig as rig type — useful when switching between PSK31 and FT8 on one IC-705 or X6100 without replugging USB CAT.

Alternative: RigCAT XML per radio (no FLrig). More setup, one less process.

Audio levels and duty cycle

From common IC-7100/705 setup notes (Fldigi wiki):

Radio in USB-D (or LSB-D on lower bands per band plan).
Adjust FLdigi TX attenuator so RF power is modest — many ops target ~30 W max on PSK for clean signals; QRP activators lower still.
Waterfall: click a trace to tune; do not transmit until the frequency is clear.

Warning: PSK31 is 100% duty cycle at full power. Reduce power and consider intermittent TX on battery activations. Heat and BMS load add up.

Portable interfaces

Options from lightest to heavier:

Setup	Weight	Notes
Phone + AndFlmsg / audio cable	Lightest	VOX PTT on some HTs; verify separation on TX
Radio USB direct	Medium	IC-705, X6100, KX3 — one cable if drivers behave
SignaLink / digirig / homebrew	Flexible	Isolation transformers reduce ground-loop hum

For SOTA-style minimalism, some ops use audio coupling without a interface on MT-63 — PSK31 deserves proper isolation if RF gets into the laptop.

Logging POTA QSOs

FLdigi can log internally and export ADIF. For POTA activations, prefer:

Polo or N3FJP as master log with MY_SIG_INFO pre-filled.
FLdigi → Configure → Logging → enable post-QSO dialog or macro that reminds you to copy call/RST to Polo.

N3FJP digital guide: set N3FJP rig control to none when FLdigi/FLrig owns CAT (N3FJP digital setup).

Mode field in ADIF should reflect actual mode (PSK31, RTTY, etc.) — awards treat them separately from FT8.

Operating tips in a park pileup

Same phone etiquette as SSB, faster cadence:

Short exchanges: call, RST, park ref if they need it, 73.
Activators: announce “PSK31” in the spot and hold a stable frequency.
Hunters: one short call; do not tune up on the activator (ethics).

Habits / gotchas / checklist (FLdigi)

FLrig on 127.0.0.1:12345. WSJT-X can use FLrig as the same CAT owner when you flip modes.
USB-D. TX attenuator for a clean PSK — 100% duty cycle cooks a QRP pack and a G90.
Spot mode PSK31 / RTTY, not SSB. Stable dial frequency.
Master log is Polo/N3FJP. FLdigi ADIF merges in Doctor like WSJT.
AC Log rig = none while FLrig has the port.
Mode tag in ADIF is PSK31 / RTTY — awards treat them as distinct from FT8.

WSJT-X (often paired via FLrig)
Software hub · Calling CQ

Notes & edits

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