CHOOSE A MODE

WTHz SIGNAL LAB / INTERACTIVE RECEIVER

Compare 7 digital radio modes
from Japan to the UK.

Radio signals on the 20 metre band can reach the UK from Japan when the ionosphere bends them back towards Earth. Choose a mode to see what it can send, how long a transmission takes and what happens as the signal gets weaker.

See what each mode sends
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.

BENCH A / MESSAGES

What each mode
sends

Choose a transmission to see the text sent over the air and what it means. FT8 and WSPR use fixed fields. The other 5 modes can carry longer text written by an operator.

TRANSMISSION SEQUENCE 6 TRANSMISSIONS
MESSAGE TYPE / FT8

Short contact with fixed message fields

FT8 sends each step as a separate message with fixed fields. Operators normally follow the sequence shown here. FT8 can also send a short free-text message.

USED FOR
Short contacts using weak signals
MESSAGE CONTENT
Call signs, grid squares, signal reports, acknowledgements and short free text
ERROR HANDLING
Checks each message and repairs some errors
TEXT SENT OVER THE AIR / FT8Typical FT8 message
CQ JA1XYZ PM95
MEANING / STEP 01

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

TERMS AND RADIO SHORTHANDWhat the shorthand means
Choose a term to see what it means.
CQcalling any stationA general invitation for anyone listening to reply.

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

BENCH B / SIGNAL WIDTH

How wide each
signal is

The top trace shows only FT8. The chart below compares all 7 modes within a 2,500 hertz (Hz) receiver filter.

CURRENT SIGNALFT8This trace shows the selected mode.
SIGNAL SAMPLE8-tone frequency-shift keying (8-GFSK)79 symbols at 6.25 symbols a second
DEMO TRACE0%
8 tonessignal formabout 50 hertzsignal width15-second turnstimingChecks each message and repairs some errorserror handling
COMPARE ALL 7 MODESChoose a row to change the signal above.
FT8 SELECTED
RECEIVER FILTER WIDTHS2,500 Hz view
012502500 Hz
COMPARE ALL 7 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 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 the 20 metre band is open between Japan and the UK. The selected mode then affects whether the receiver can recover a weak signal.

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 makes short, structured contacts.
  • JS8Call, PSK31, RTTY and Olivia send typed messages.
  • Feld Hell displays received text as dots for the operator to read.