CHOOSE A MODE

WTHz SIGNAL LAB / INTERACTIVE RECEIVER

Compare 9 digital radio modes
from Japan to the UK.

This page uses the 20 metre band — amateur-radio frequencies around 14 MHz — as one shared example. Its name describes the radio wavelength, not how far a signal can travel. When conditions are right, the ionosphere bends the signal back towards Earth, allowing it to reach the UK from Japan.

See what goes over the air
JAPANPM95
UNITED KINGDOMIO81
9,634 kmgreat-circle distance*
SELECTED MODEFT8Short contacts using weak signals
MODEFT8SIGNAL WIDTHabout 50 hertzTIMING15-second turns

*This example uses a path from Tokyo to the Bristol area. Actual paths can bend, split and change as ionospheric conditions change.

A SHORT HISTORYFT8
WHY IT APPEARED

A faster weak-signal contact

FT8 appeared in WSJT-X in 2017. Its name means Franke–Taylor, 8-frequency shift keying. It shortened the minute-long turns used by earlier weak-signal modes, making a basic contact much quicker.

CREATED BY
Joe Taylor, K1JT, and Steve Franke, K9AN
DESIGNED TO
Complete structured contacts in 15-second turns
ARRL: FT8 in WSJT-X ↗

BENCH A / MESSAGES

What goes over
the air

Choose a mode from the menu at the top of the page. Then step through an example to see the text sent over the air and what it means.

TRANSMISSION PLAYER / FT8 STEP 01 OF 06
EXAMPLE EXCHANGE

An FT8 contact from Japan to the UK

6 short, structured transmissions

TYPE
STRUCTURED CONTACT
LENGTH
6 TRANSMISSIONS
TURN OR FLOW
15-SECOND TURNS
ON-AIR TEXT / FT8JAPAN → ANY STATION
CQ JA1XYZ PM95
WHAT THIS MEANS / STEP 01

JA1XYZ is calling any station and gives its grid square, PM95.

CQ
calling any stationA general invitation for anyone listening to reply.
PM95 / IO81
grid squaresFour-character Maidenhead grid squares show a broad area, not an exact location.
See the complete exchange6 transmissions
See all terms and radio shorthand6 terms
CQ
calling any stationA general invitation for anyone listening to reply.
PM95 / IO81
grid squaresFour-character Maidenhead grid squares show a broad area, not an exact location.
-15 / -18
signal reportsThese figures compare the signal with the background noise. A more negative figure means a weaker signal.
R
report receivedR confirms the earlier report. In R-18, −18 is the new report sent in reply.
RRR
reports receivedConfirms that both signal reports were received correctly.
73
best regardsA traditional friendly sign-off at the end of a radio contact.

These examples show what an operator reads. They do not show every bit sent by the software. The typed conversations are examples.

BENCH B / SIGNAL SHAPE AND WIDTH

How each mode
changes the signal

The teaching trace shows how FT8 carries data. Play it to follow the selected on-air message, then compare the width and transmission time of all 9 modes.

CURRENT SIGNALFT8Teaching diagram for the selected mode.
HOW THIS MODE CARRIES DATA8-tone frequency-shift keying (8-GFSK)79 symbols at 6.25 symbols a second
TRANSMISSIONSYMBOL 1 / 79TONE 7 OF 8
WHAT CHANGESFrequencyAVAILABLE STATES8 tonesOne symbol0.16 seconds
ON-AIR MESSAGE / STEP 01JAPAN → ANY STATION
TEACHING PROGRESS0%The whole structured message is encoded together. Letters do not map to individual tones one by one.
WHAT TO NOTICEFT4 uses the same structured-message family, but sends it faster

FT8 sends one of 8 closely spaced tones every 0.16 seconds. The order of those tones carries the message.

This is a teaching diagram, not a recording.
8 tonessignal formabout 50 hertzsignal width15-second turnstimingChecks each message and repairs some errorserror handling
COMPARE ALL 9 MODESChoose a row to change the signal above.
FT8 SELECTED
RECEIVER FILTER WIDTHS500 Hz close-up
0250500 Hz
COMPARE ALL 9 MODES / TRANSMISSION TIMEFT8 selected / 0 to 120 seconds
0306090120 s

BENCH C / NOISE

What noise does
to each mode

Move the signal-to-noise ratio control, then choose another mode. FT8, FT4 and WSPR accept or reject a complete transmission. Other modes may lose characters, message blocks or dots.

SIGNAL-TO-NOISE RATIO (SNR) / 2,500 HZ REFERENCE
-18dB
WeakerStronger
RECEIVED TEXT / FT8CQ JA1XYZ PM95
TRANSMISSION DECODED-18 dB
WHAT NOISE DOES

The decoder either recovers a complete message or rejects it.

ERROR HANDLING
Checks each message and repairs some errors
RECEPTION
About −21 dB in WSJT-X test conditions
SIGNAL WIDTH
about 50 hertz

Do not use these figures to rank the modes. They come from tests with different message lengths, decoder settings and operating conditions.

BENCH D / RADIO PATH

How the signal
reaches the UK

The ionosphere determines whether this 20 metre path is open between Japan and the UK. The selected mode then affects whether the receiver can recover a weak signal. All 9 modes can also be used on other amateur bands, where the path and range will differ.

F REGION OF THE IONOSPHERE
JA1XYZJapan / PM95
G0ABCUK / IO81
EXAMPLE PATHABOUT 9,634 KMSeveral ionospheric hops
SELECTED MODEFT8

Short contacts using weak signals

WHAT IT SENDS
Call signs, grid squares, signal reports, acknowledgements and short free text
SIGNAL
8-tone frequency-shift keying (8-GFSK), about 50 hertz
TRANSMISSION TIME
12.64-second transmission in each 15-second turn
WEAK-SIGNAL RESULT
The decoder either recovers a complete message or rejects it.

OPERATING NOTE

Choose a mode for what you need to send

Each mode suits a different task:

  • WSPR tests where a signal can be heard.
  • FT8 and FT4 make short, structured contacts; FT4 favours speed.
  • JS8Call, RTTY, PSK31, MFSK16 and Olivia send typed messages.
  • Feld Hell displays received text as dots for the operator to read.