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WSJT FT8 Weak Signal Mode Works Great

wsjt ft8 weak signal mode

I just dipped my toe in the water with the new WSJT FT8 weak signal mode. It works great, and on low power, too. 

Have you started using the new weak signal modes yet? Joe Taylor, K1JT is an astrophysicist at Princeton University. He is a Nobel laureate and a ham radio operator. For many years, Joe has been developing special digital radio modes for weak signal communication over long distance in space and on Earth.  His ideas have been packaged into open source software for use by hams and other experimenters. WSJT-X is the latest version which supports numerous modes and connects to radios and other software used by hams.

In general, weak signal contacts use very narrow bandwidth tones at very low speeds. The new FT8 mode uses 8 tones in a 50 Hz bandwidth. Each message has only 75 bits and is transmitted within a 15 second timing window. Other WSJT-X modes such as JT65 and JT9 are even better for weak signal exchanges, but run much slower in 60 second timing windows. Weak signal modes also include special synchronization and error correction codes. If you are going to use these modes, you need to make sure that your computer clock is synchronized to a time standard.

Some hams don’t like the restricted information exchanges or the automation of contacts. I understand that. But, each mode has its place. So far, I am seeing tons of FT8 signals on all bands (40 through 17 meters) from all over the world. This new mode has become very popular since last summer because it is a lot faster.

WSJT FT8 Weak Signal Mode – Up and Running

This stuff is easy to use. It only took ten minutes to download and install WSJT-X, as well as connect it to my DX Labs Suite radio control and Flex Radio 6300 transceiver. I am going to use these modes with low power, around 10 watts. A screen capture of my first two contacts on FT8 are shown above. Both took place on 20 meters.

As you can see, the WSJT FT8 weak signal mode uses a minimal qualifying QSO. Namely, you exchange call letters, locations and signal reports and confirm their reception. The nice thing about WSJT-X is that it monitors your activities and sends the correct responses automatically.

Cameron, W1CAM in Omaha, Nebraska provided my first contact. DO20 is my grid square location and EN11 is his. We exchanged signal-to-noise reports of -5 and -6 dB, then said 73 or best wishes and goodbye. Similarly, I next responded to a call from Jim, W5ZIT in Farmersville, Texas.

In the picture, you can see all of the signals received on the left side. These are spread over the entire 3 kHz FT8 bandwidth. On the right side, you can see the signals on my current receiving frequency. If you want to see FT8 in action, check out this video from K5ACL.

WSJT FT8 Weak Signal Mode – Time Synchronization

By the way, I have noticed that synchronization of your PC clock is very important with FT8. The synchronization built into Windows 10 (if you turned it on) is not good enough. It only runs once a day by default. Without keeping your clock less than one second off with an internet time source, the quality to FT8 decoding declines a lot.

Try using the NTP client from Meinberg. That worked for me.


  1. Dwight Hazen says:

    FT8 for me has opened a new digital mode for me. Many years ago when PSK31 came about I was into that for a while but now FT8 has taken hold and I am starting to use all the tools. I finally got around to using Log Book of the World, QRZ logbook, gray line, when to change bands when to call CQ and when to answer a CQ. You get fast feedback from decisions you make due to the fast turnaround time between transmit and receive. And yes your computer clock has to be dead on. No internet to set your clock? Use WWV or an atomic clock that every ham station should have.

    I see complaints about people running too much power. I found a simple way to determine if you are guilty look at the difference between the two signal levels. If you are receiving at -10 and the other station is hearing you at +15 you may be running too much power. I find the best compromise for me is the 10-20w level on my 80/40 dipole. Others may need more or less. If you have an SDR receiver overload should not be a problem.

    Is FT8 a mindless mode? I think not, it’s sort of like contesting as to the exchange of contact information only but I think FT8 is lot more fun. You can learn a lot from any mode of operation don’t get stuck in a rut. Try it!

    Dwight WB9TLH

    (I am not a contester but I might turn into one hi hi)

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