FM-FT8 – FT8 via FM on 2 m: an easy way into digital modes

Published 15 November 2026 · Tobias Johnson, DL1TJ

Proposal FM-FT8 is standard FT8 run through ordinary FM radios on 2 m, so anyone with a handheld and a computer can make their first FT8 contacts without an expensive SSB rig. Proposed experimental calling frequency: 144.575 MHz.

This is an experimental proposal put up for discussion, not an established convention. 144.575 MHz is not allocated to FT8 and not coordinated with any band plan authority; the frequency may change with feedback, and nothing here has been tested on the air yet.

Why

FT8 is the most approachable digital mode we have: structured messages, automatic sequencing, and contacts that complete and log themselves. On 2 m, though, it is run on SSB, and that is a barrier.

• An SSB-capable 2 m transceiver costs many times what an FM handheld does.
• Most newcomers, including Class N licensees who start on 2 m, own only an FM radio.
• So the people who would enjoy FT8 most as a first step cannot try it.

FT8 is only audio. Any FM radio can carry it, with the WSJT-X software everyone already uses. What is missing is an agreed calling frequency.

A proposed experimental calling frequency

144.575 MHz lies in the 2 m all-mode segment (144.500 to 144.794 MHz), where the IARU Region 1 band plan allows FM. Neither the IARU nor the DARC plan assigns it a specific use. It sits just below the data centre of activity on 144.600 MHz and deliberately leaves that frequency free for the narrow modes that meet there.

Reference setup for the experiment

So that tests can be compared, everyone starts from the same configuration:

Before you transmit

• Check first: local activity on the frequency, the rules of your licence and country, and the current IARU Region 1 band plan.
• Listen first. It is a shared frequency, not a reserved or exclusive one, and it may be in use or unsuitable where you live.
• One at a time. Do not transmit in a time slot another station is using, and let a running contact finish. Two FM signals at once block each other, as explained below.
• Attended operation only; this segment does not allow unmanned stations.
• Stay off 144.174 MHz, where FT8 is run on SSB. FM and SSB stations cannot decode each other, and FM there would disturb the SSB users.

A skimmer that listens around the clock

So that the frequency has a listener from day one, I have set up a receive-only FT8 skimmer at my station DB0RBX in Regensburg (JN69ba). It listens on 144.575 MHz FM 24/7 and shows every FT8 message it decodes at fmft8.db0rbx.de ↗. If you are within FM range of Regensburg, you can check there whether your signal gets out.

What to expect

This is an entry point, not weak-signal work. FT8 on SSB decodes far below the noise; through an FM receiver most of that advantage is lost.

• Range: about what FM voice reaches on the same radios, perhaps a little more.
• One station per slot: FM receivers lock onto the strongest signal, so you will usually decode one station at a time, not a full waterfall. That is no deal breaker: unlike on HF, range on 2 m is local, so only a few stations share the frequency anyway.
• What you do get: the complete FT8 experience. Calling CQ, automatic exchanges, grid squares, logging, and spots on PSKReporter. And you gain experience: with the software, the timing and the operating habits, all of which carry over unchanged to FT8 on SSB and HF.

For range and DX, SSB remains the upgrade path. FT8 via FM is where you learn the mode with the radio you have.

How FM differs from SSB for FT8

On SSB the receiver hands everything it hears to the computer unchanged, so WSJT-X sees many stations side by side and can pull single ones out of the noise. An FM radio does more to the signal on the way. Four things matter. The explanations follow from how FM radios work; how much each one matters in practice still has to be measured.

Capture effect: the strongest signal wins

When two stations transmit on the same FM frequency at once, the receiver locks onto the stronger one and suppresses the weaker. If both are about equally strong, the result is garbled and neither decodes. On SSB, dozens of FT8 stations share a frequency in the same time slot, each on its own audio tone. Via FM that does not work: expect one contact at a time within range, and no pile-ups. Hence the rule to transmit only in a free slot.

Audio processing: built for speech

FM radios shape the audio for voice. The transmitter boosts high tones (pre-emphasis) and the receiver lowers them again (de-emphasis); filters cut off the lowest and highest tones, roughly below 300 Hz and above 3 kHz; and a limiter clips audio that is too loud. FT8 sends one tone at a time within a span of only 50 Hz, so the tone shaping should do little harm as long as the signal sits in the middle of the audio range. That is why step 4 suggests 1000 to 2000 Hz. Clipping is the thing to avoid: it distorts the tone and adds unwanted tones at multiples of its frequency. Keep the transmit level moderate, as in step 6.

PTT timing: start on time

FT8 runs in fixed 15-second slots, and a transmission fills almost 13 seconds of its slot. The decoder tolerates a timing error of roughly a second. An FM radio needs a moment to get on the air after PTT, and VOX adds to that, because it keys the radio only once it hears audio; it can also drop out in the middle of a transmission. A cable through which WSJT-X keys the radio directly (hardware PTT) starts on time, every time. Use VOX only if there is no other way. On receive, battery save does similar damage: it can cut off the start of a transmission, so switch it off.

Narrow FM: a starting point

Narrow FM, the 12.5 kHz setting, is the reference because it takes up the least room next to the neighbours on the band. It is a starting point, not a measured optimum. How far a given audio level swings the transmitter (the deviation) differs from radio to radio, and a narrow signal sounds quieter on a receiver set to wide. So set both stations the same way, and test levels on the air instead of assuming them.

None of this brings back what FT8 can do on SSB. FT8 via FM does not have the weak-signal performance of FT8 on SSB, and it is not meant to.

Step by step

1Get the three things you need

• An FM radio for 2 m. A handheld is enough.
• A computer with WSJT-X ↗ installed (free; Windows, macOS, Linux).
• An audio cable with PTT between the two: a sound-card interface that fits your radio's speaker/microphone socket.

2Set up the radio

• Tune 144.575 MHz, FM, simplex (no repeater shift). Select narrow FM (12.5 kHz) if the radio offers it.
• Open the squelch fully. A closed squelch hides weak stations from the decoder.
• Switch off battery save, CTCSS/DCS tones and any roger beep.
• Select low power. FT8 transmits for about 13 seconds at a time, every other slot, and handhelds get warm at full power.
• Use a vertical antenna, as on any FM simplex channel.

3Set the computer clock

FT8 works in fixed 15-second slots, so your clock must be right to within a second. Switch on automatic internet time in the operating system.

4Set up WSJT-X

• Settings > General: enter your callsign and grid locator.
• Settings > Radio: Rig “None”. PTT via the cable's serial port (RTS or DTR), so that WSJT-X keys the radio itself. Use VOX only as a fallback if your cable has no PTT line: it starts late and can drop out.
• Settings > Audio: choose the cable's sound device for both input and output.
• Settings > Frequencies: add 144.575 MHz for FT8, then pick it in the main window, so your log shows the right frequency.
• Main window: mode FT8, transmit tone between 1000 and 2000 Hz on the waterfall.

5Check that you receive

With the squelch open you should see noise across the waterfall. Adjust the radio's volume until WSJT-X's level meter reads roughly 30 dB. If another station is on, its messages appear in the Band Activity list at the end of each slot.

6Set your transmit level

Start with the WSJT-X power slider low and raise it only until another station, or a second receiver of your own, decodes you. Too much drive makes the radio clip the tones, which distorts your signal and can keep others from decoding you. Near Regensburg, the skimmer ↗ shows whether you are decoded.

7Make a contact

• Answer a CQ: double-click it in the Band Activity list. WSJT-X sends your call and locator, then the reports and 73, on its own.
• Call CQ yourself: click the CQ message, then Enable Tx. When someone answers, the exchange runs automatically.
• Log it: confirm the log window that opens when the contact is complete. It is an FT8 QSO on 2 m like any other, and you can upload it wherever you keep your log.

70 cm works the same way

Everything above applies on 70 cm as well: same radio settings, same WSJT-X setup. No frequency is suggested for 70 cm yet. The idea starts on 2 m, where more FM radios and more listeners are.

Where FM-FT8 is going

The project has three stages. Only the first is happening now; the other two are plans and ideas, not things that exist.

NowA. Standard FT8 via FM

The current experiment, and the subject of this page. The goal is to show that standard, unmodified FT8 can be sent and received with inexpensive, ordinary FM radios. What exists so far is this proposal, the reference setup and the skimmer. On-air contacts and measurements are still to come.

ResearchB. A digital mode made for FM

FT8 was designed for SSB. It is used here because the software and the operating habits already exist, not because it suits FM well. FT8 squeezes into 50 Hz because bandwidth is scarce on SSB and a narrow signal reaches far there. An FM channel behaves differently: once a signal is strong enough for the receiver, some 2.5 kHz of clean audio is available, and below that point nothing gets through, however narrow the signal. A new protocol designed around this could aim for:

• Shorter transmissions: the same message in a second or two instead of 13, so handhelds stay cool and several stations can share one time slot, one after another.
• Robust decoding with forward error correction, in spite of what FM radios do to audio.
• Efficient use of a single narrow FM channel.
• Compatibility with inexpensive handhelds, through the same audio cable.
• The FT8 message format, so calling CQ, reports, locators and logging stay the way operators know them.

A second route leaves the FM radio behind: LoRa, a chirp spread-spectrum modulation that still decodes below the noise, which is exactly the ability FT8 loses through an FM receiver. It needs its own transceiver module. Boards for 70 cm cost about as much as a cheap handheld and already carry LoRa APRS. An FT8-style exchange on top of LoRa could be an equally cheap way in, with real range, but the radio people already own would no longer do the job.

All of this is a direction for research. No such mode exists, and it would need new software at both ends. That is why the project starts with plain FT8: it works today, with what everyone already has.

Long termC. Accessible digital amateur radio

The larger aim behind both: digital amateur radio that does not need expensive equipment. What could grow out of it:

• A reference audio and PTT interface that anyone can rebuild.
• Compatibility tests across common handheld radios.
• Documented reception results from real use.
• Open technical documentation.
• Participation from the community, especially Class N and Class E licensees.

Feedback and test reports welcome: dl1tj@darc.de.