Getting started with FT8: setup, sequencing and settings
Fifteen second slots, a computer that knows the exact time, and a mode that decodes signals you cannot hear.
The short answer
FT8 needs a radio, a computer running WSJT-X, a sound and control interface such as a digital mode interface, and a clock accurate to under a second. Contacts run in 15 second slots and exchange only callsigns, a signal report in decibels and a grid square. It decodes signals roughly 20 dB below what a human ear can pull out of noise.
- Slot length
- 15 seconds
- Bandwidth
- 50 Hz per signal
- Decode threshold
- About -21 dB
- Clock accuracy
- Under 1 second
- Typical power
- 20 to 50 W
- Duty cycle
- 100 percent
FT8 changed what a small station can do. It encodes a fixed, tiny message into a 15 second transmission occupying about 50 Hz, and the decoder pulls it out of noise roughly 20 dB below the point where a human ear gives up. A 25 W station with a wire in a tree works the world on FT8 in conditions where SSB produces nothing at all.
What it does not do is teach you to operate. The exchange is fixed, the software clicks through it, and there is no conversation. Plenty of operators use it as the mode that keeps the station useful during poor conditions and use voice or CW when the bands are good. That is a sensible way to think about it.
This page covers the hardware chain, the two settings that cause almost every problem, and how a contact actually sequences.
What you need
- A radio with a data connection
- Anything with a rear data or accessory port. Modern radios such as the Icom IC-7300 and the Xiegu G90 put a sound card and CAT control on a single USB cable, which removes the interface question entirely.
- An interface, if the radio does not have one built in
- A Digirig Mobile digital modes interface or a Tigertronics SignaLink USB interfacenot on amazon provides isolated audio in and out plus keying. Isolation matters because a direct connection between radio ground and computer ground invites hum and RF problems.
- WSJT-X, or a program built on it
- Free, cross platform, and the reference implementation. JTDX and other variants exist and behave similarly.
- An accurate clock
- FT8 slots are aligned to the wall clock. If your computer time drifts more than about a second, you decode nothing and nobody decodes you. Enable network time and verify it, because a laptop that has been asleep often has not resynced.
- Your grid square
- A four character Maidenhead locator such as DM79. It is part of the exchange and the software needs it in the settings before you start.
The two settings that cause most problems
Almost every FT8 difficulty is one of these, and both are about audio level rather than radio frequency.
The receive side has an equivalent. Set the computer input level so the WSJT-X spectrum noise floor sits around 30 dB on the scale, with the display showing a flat green band and no red clipping. Too low and weak signals never decode; too high and the decoder is swamped by intermodulation of its own making.
- Turn off speech processing, noise reduction and any transmit equalisation. FT8 is a data mode and every audio process degrades it.
- Use the data or USB-D mode on the radio rather than plain USB where the radio offers one, because it bypasses the microphone chain.
- Set the radio to a fixed filter bandwidth of around 3 kHz. Narrow filters cut off signals in the upper part of the passband and you decode fewer stations for no reason.
- Split operation or the software fake-it option keeps your audio tone in the cleanest part of the passband. Leave it on.
How a contact sequences
A full FT8 exchange is four or five transmissions of 15 seconds each, alternating between even and odd slots. The software builds every message.
The exchange
A standard FT8 contact, transmission by transmission
| Slot | Who | Message | Meaning |
|---|---|---|---|
| 1 | Them | CQ W1XYZ FN42 | Calling anybody, from grid FN42 |
| 2 | You | W1XYZ KX0ABC DM79 | Answering, here is my grid |
| 3 | Them | KX0ABC W1XYZ -12 | You are 12 dB below their noise reference |
| 4 | You | W1XYZ KX0ABC R-08 | Roger, and you are 8 dB down here |
| 5 | Them | KX0ABC W1XYZ RR73 | Confirmed, best regards, contact complete |
The signal report is a signal-to-noise ratio in decibels relative to a 2.5 kHz reference bandwidth, not an S meter reading. Minus 20 is a perfectly good contact. Minus 24 is near the decoding floor.
Your first FT8 contact
- 1
Confirm the clock
Check your system time against a known accurate source. Decodes that appear consistently one or two seconds late in the display are a time sync problem, not a propagation one.
- 2
Tune to an FT8 frequency and watch
The common ones are 7.074, 14.074, 18.100, 21.074 and 28.074 MHz. Sit for a few minutes and confirm you are decoding stations. If the waterfall shows signals but nothing decodes, it is the clock.
- 3
Set your power and check ALC
Use the tune button, watch the ALC and back the audio down until it stops moving. Do this once per band.
- 4
Double click a CQ
The software takes over, answers in the right slot and steps through the exchange. Watch what it sends rather than clicking away.
- 5
Let it finish, then log it
WSJT-X logs automatically to its own file and can push to most logging programs. See logging and confirming contacts for what happens next.
What FT8 does to your equipment
A continuous carrier at high duty is the hardest thing you can ask of a transmitter. Radios rated for 100 W SSB are generally rated far lower for continuous duty, and running FT8 at full output cooks finals over time.
- Run 30 to 50 percent of rated output. On FT8 that costs you almost nothing in contacts and roughly doubles the working life of the radio.
- Give the radio airflow. A cheap fan aimed at the heat sink is a sensible addition for a digital station.
- Size the power supply for continuous current, not peak. A supply that sags under a 20 A continuous draw is a supply that will fail. See sizing a power supply.
- A Powerwerx SS-30DV desktop power supply handles a 100 W radio at digital duty. A Astron RS-35M-AP linear power supply linear supply handles it without breaking a sweat and produces no switching noise.
Gear for a digital station
The digital chain
Interface, radio and a supply that does not object to continuous current.
Digirig
Digirig Mobile digital modes interface
A tiny combined sound and CAT interface. The simplest way to add digital modes to a radio without a built-in USB codec.
Check price$64.95
Tigertronics
Tigertronics SignaLink USB interface
The long-standing isolated interface with a level knob on the front, which makes setting drive far easier than a menu dive.
Sold by Tigertronics, not Amazon. The link searches the category.
Icom
Icom IC-7300
Sound card and CAT control over one USB cable, plus a scope that shows you which FT8 slots are busy.
Check price$1,255.74
microHAM
microHAM USB III interface
A full station interface for a rig without USB, handling audio, keying and CAT with proper isolation throughout.
Sold by microHAM, not Amazon. The link searches the category.
Astron
Astron RS-35M-AP linear power supply
A linear supply with no switching noise, which matters more on digital modes where the noise floor decides what decodes.
Check price$551.00
Xiegu
Xiegu G90
A 20 W radio with a built-in tuner that handles digital modes comfortably at reduced power.
Check price$466.00
Common questions
Questions people ask about this
Why am I seeing signals in the waterfall but decoding nothing?
Nine times out of ten it is the computer clock. FT8 slots are aligned to the wall clock and a drift of more than about a second stops decoding entirely. Enable network time synchronisation and verify it after the machine wakes from sleep, since laptops frequently do not resync automatically. The other cause is an input level so high the audio is clipping.
How much power should I run on FT8?
Between 20 and 50 W for a radio rated at 100 W. FT8 is essentially full duty cycle, so running full output heats the finals continuously and shortens their life. The mode decodes signals around 21 dB below the noise floor, so the difference between 25 W and 100 W is roughly one contact in twenty, and it costs you the radio.
What does a signal report of minus 15 mean?
It is a signal-to-noise ratio in decibels referenced to a 2.5 kHz bandwidth, not an S meter reading. Zero would be a signal equal to the noise in that bandwidth. Minus 15 is a strong, reliable FT8 signal. The decoding floor is around minus 21 to minus 24 depending on conditions, so anything above minus 20 is a comfortable contact.
Does FT8 count for awards?
Yes, for most awards on most programs. Confirmations flow through electronic logbook services automatically, which is part of why the mode grew so quickly. Some operators feel a mode where the computer conducts the exchange is a different activity from operating, which is a fair opinion and does not change the award rules.
Can I run FT8 on a Technician license?
On the parts of the spectrum where Technicians have digital privileges, yes. That includes the 10 metre band segment allocated to Technicians and all the VHF and UHF bands. For the popular HF FT8 frequencies on 40, 20 and 15 metres you need a General license. Ten metre FT8 during high solar activity is genuinely productive for a Technician.
Keep going
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