FT8 Troubleshooting: Decodes but No Replies

If WSJT-X decodes a full band but nobody answers you, the receive side works and the problem sits somewhere in your transmit chain or your operating habits. The usual causes are a wrong audio output device, too much drive, a computer clock that has drifted, or calling right on top of the station you want. This guide is written for WSJT-X 3.0.2, the current general availability release on the official WSJT-X site, and every setting named below matches the 3.0.2 User Guide.

What is actually happening

Decoding proves only half of the station. It shows your receive audio, your waterfall and your decoder are fine. It says nothing about whether audio reaches the radio on transmit, whether the radio keys up, or whether the signal it sends is clean and on time.

FT8 runs in 15-second periods, so a station that answers you has a few seconds to see your call and decide. Anything that makes your signal late, dirty, buried under other callers or sent in the wrong period costs you that reply. If you are still new to the mode, read the complete FT8 beginner's guide first, because this article assumes you already know how a standard exchange runs.

Setup checks before you touch any setting

The WSJT-X User Guide has a short Pre-QSO checklist. I would go through it line by line before changing anything else:

• Your callsign and grid locator are correct under File, Settings, General. The guide prefers the 6-character locator.
• PTT and CAT control are configured and tested. On the Radio tab, Test CAT should turn green and Test PTT should turn red when the radio keys.
• The computer clock is synchronized to UTC within ±1 s.
• Audio input and output devices run at 48000 Hz, 16 bits.
• The radio is in USB, or the Data/Pkt mode that enables its rear-panel audio input.
• Receive filters are centered and set to the widest passband available, up to 5 kHz.

If you built the station recently, compare it against our FT8 station setup walkthrough for radio, sound card and software. A missed step there shows up here as silence.

The wrong Tx audio device

This is the classic cause. The radio keys, but WSJT-X is sending its tones to your laptop speakers or a headset. On the Audio tab, Output must be the radio's USB CODEC or your interface, not the computer's default device. The guide adds a warning worth repeating: if the output device is also the computer's default sound device, turn off all system sounds so you do not transmit notification chimes.

On Windows, radios with a built-in USB CODEC based on the TI PCM2900 series can be set up as a microphone input instead of a line input. The guide says to set the mic level to 0 dB in the Recording Device Properties for those devices. If you use an external box, our comparison of SignaLink, Digirig and built-in sound card interfaces explains how each one connects.

Transmit audio source on the radio

Some radios let WSJT-X choose which connector accepts Tx audio. On the Radio tab, Transmit Audio Source picks Rear/Data or Front/Mic. If the radio expects audio on the rear data port and the software sends it elsewhere, you key up with no modulation.

Settings that matter

Drive level and the Pwr slider

The User Guide's method is simple. Click Tune, listen to the tone on your radio's monitor and make sure it is perfectly smooth, with no clicks or glitches, even while the computer does other work. Then pull the Pwr slider at the right edge of the main window down from maximum until the RF output falls slightly. That is generally a good drive level.

My view: if your output does not change at all as you move the slider near the top, you are driving too hard. The WSJT-X FAQ notes that too much audio level can generate in-band harmonics. Our guide to getting digital mode audio levels right goes further on the receive side and the transmit side together. Tick Remember power settings by band on the Audio tab if you change bands often.

Split Operation: Rig or Fake It

On the Radio tab, set Split Operation to Rig if your radio supports split through CAT, or Fake It to let WSJT-X shift the VFO itself at T/R switching. Either way, WSJT-X keeps the Tx audio in the 1500 to 2000 Hz range so audio harmonics cannot pass through the transmit sideband filter. The guide calls the result a cleaner transmitted signal. Choose None only if you have a reason.

Two side effects confuse people. With split on, the radio's dial frequency may jump when you transmit if your Tx audio frequency is outside 1500 to 2000 Hz. The FAQ says this is normal. Second, many Icom radios cannot report their split status or VFO, so with those you should not change the VFO, split or dial from the front panel while WSJT-X runs. A green circle with an S next to the dial frequency confirms split is active.

Where you transmit on the waterfall

The red marker on the waterfall is your Tx frequency, and your on-air frequency is the dial plus that audio offset. The guide is direct about this: to avoid QRM from competing callers, it is usually best to answer a CQ on a different frequency from the CQing station. Pick a clear spot and tick Hold Tx Freq so a double-click does not drag you back onto someone else. Shift+F11 and Shift+F12 move your Tx frequency down or up in 60 Hz steps. Reading the waterfall well helps here, and our waterfall reading guide shows what a clear gap looks like.

A plain double-click on a decoded CQ moves the green Rx marker to the caller. Holding Shift moves only the Tx marker, and holding Ctrl moves both. If you Ctrl-click by habit, you land on the DX's own frequency every time.

Even and odd periods

Tx even/1st decides whether you transmit in the even or odd periods. Double-clicking a decoded line sets it correctly for you. If you set up a call by hand, or typed the callsign into DX Call, check that box. Transmitting in the same period as the station you call means they are transmitting while you are, so they can never hear you.

Auto Seq and Enable Tx

With Auto Seq checked, WSJT-X steps through the exchange as replies arrive. It also turns Enable Tx off at the end of each QSO, so the next call needs you to start it again. The guide calls auto-sequencing an operator aid, not an operator replacement. If Double-click on call sets Tx enable is off on the General tab, a double-click prepares the messages but you still have to press Enable Tx.

Troubleshooting list, in order

Work down this list one step at a time and test after each change.

1. Confirm call and grid. Open Settings, General and check every character of your callsign and your grid locator. If you use a compound callsign, call with Tx1 rather than Tx2 so the other station decodes your call in full.
2. Test CAT and PTT. On the Radio tab, Test CAT must turn green and Test PTT must key the radio. If you use VOX, check T/R switching with the Tune button instead.
3. Check the audio output device. On the Audio tab, Output must be the radio's CODEC or your interface at 48000 Hz, 16 bits, with system sounds turned off if it is also the default device.
4. Set drive with Tune. Listen for a smooth tone with no clicks, then lower the Pwr slider from maximum until RF output falls slightly.
5. Turn on split. Set Split Operation to Rig or Fake It, then look for the S in the green CAT indicator.
6. Check the clock. Your computer must be within ±1 s of UTC. The DT column shows each decode's time offset in seconds, so check it on every decode.
7. Move off the DX. Put your Tx marker on a clear part of the waterfall, not on the station you are calling, and tick Hold Tx Freq.
8. Check the period. Make sure Tx even/1st is the opposite of the station you are calling. Double-click their CQ to set it automatically.
9. See where you are heard. Enable PSK Reporter Spotting on the Reporting tab, call CQ for a few periods and check the PSK Reporter map for your call.
10. Look at the antenna and band. If PSK Reporter shows few or no spots, use Tune to check your tuner and output, then consider whether the band is open to where you are calling.

Reading the PSK Reporter result

PSK Reporter gathers reception reports from WSJT-X and other programs and shows them on a world map in near real time. I find it the fastest way to split "nobody hears me" from "they hear me but do not answer".

My read: spots in the right direction but no replies point back to operating, such as calling on the DX's frequency or in the wrong period. No spots at all after several CQs point to the transmit chain or the antenna. In that case, recheck steps 2 to 5, then look at matching with our antenna tuner explainer and at timing with our guide to how HF propagation changes through the day.

Power is rarely the answer. The User Guide reminds you that under most HF conditions QRP is the norm for these modes. I would fix a clean signal and a clear frequency long before I turned the power up.

Clock errors deserve their own check

The guide is strict about time. It wants the PC clock within ±1 s of UTC, and it says the built-in Windows time service may not be adequate. It recommends the Meinberg NTP Client and warns against tools that correct the clock in periodic steps, because WSJT-X needs a clock that never steps backwards and changes smoothly. A clock that looks right is not enough. If your DT values look wrong, fix that before anything else. The next guide in this series, FT8 Time Sync: Fixing DT Errors, covers it in detail.

If you run an IC-7300, remember that many Icom radios cannot report split status, and our full IC-7300 review covers the radio itself.