FT4 Mode Guide: Speed, Sensitivity and How It Differs From FT8

Almost everybody knows FT8, but its faster sibling is much less used outside contests. The FT4 mode was built for one job: making short, contest-style contacts on HF and 6 meters at roughly twice the speed of FT8. It shares the same program, WSJT-X, and the same family of 77-bit messages, so a station that can run FT8 can run FT4 within a minute of changing the mode menu. This guide explains what FT4 actually is, how its numbers compare with FT8, which contests use it, how to configure it, and when you are better off staying with FT8. The technical numbers come from the WSJT-X 3.0.0 user guide, and the contest details from the published rules.

Where FT4 Fits in the WSJT Family

The WSJT-X user guide describes a ladder of modes with different time sequences. The older JT4, JT9 and JT65 modes use one-minute sequences, so a minimal contact takes four to six minutes. FT8 is four times faster, with 15-second sequences, and a few decibels less sensitive. FT4 is faster still, with 7.5-second sequences, and the guide describes it as especially well suited for radio contesting. FST4, by contrast, is designed for the LF and MF bands, and the guide warns you not to confuse FST4 with FT4, which has a very different purpose.

All the newer modes carry 77 bits of information, including FT4, FT8, FST4, Q65 and MSK144. Five of those bits are used to flag special message types, such as nonstandard callsigns, contest exchanges and DXpedition mode. That shared design explains why the same decoder, the same logging and the same alert tools work across the modes. If you want an overview of the whole range of choices, our article on digital modes beyond FT8 compares FT4 with JS8Call, PSK31 and RTTY.

The Numbers: FT4 Versus FT8

According to the WSJT-X guide, compared with FT8, FT4 is 3.5 dB less sensitive and requires 1.6 times the bandwidth, but offers the potential for twice the QSO rate. The protocol table in the same guide gives the details, which are summarized here.

The threshold is the signal-to-noise ratio, in a 2500 Hz reference bandwidth, at which a message has at least a 50 percent chance of being decoded. A difference of 3.5 dB is not enormous; it means that a signal that FT8 can just decode would need to be a little more than twice as strong in power terms for FT4 to copy it. In real conditions on busy HF bands, where most signals are well above the threshold, this penalty seldom matters. When the band is thin and you are chasing weak DX, it can matter a great deal, and FT8 will win.

The speed advantage works in the opposite way. A minimal FT8 contact needs several cycles of 15 seconds, while FT4 does the same exchange in half the time. In a contest, the difference between a one-minute and a half-minute contact is the difference between a decent rate and a poor one. If you are curious about the effect on the band, note that FT4 signals are wider: at 83.3 Hz, five signals will fit in the space of about eight FT8 signals, so packing is slightly less dense, but the shorter occupancy means a given frequency is reused more often.

Contests That Use FT4

The WSJT-X guide lists the contests that have special message formats: the North American VHF Contest, the European VHF Contest and the ARRL Field Day for FT4 and FT8, together with FT Roundup, WW Digi and the ARRL International Digital Contest. Each has its own exchange, and WSJT-X can generate the right messages and auto-sequence them if you select the operating activity on the Advanced tab of the settings. For example, the North American VHF and ARRL International Digital contests use CQ TEST, callsign and grid, with a rover signaling by adding /R to a callsign.

One of the best examples is the WW Digi DX contest, which uses FT4 and FT8 on six HF bands with a four-character grid exchange. Its rules recommend sub-bands that place FT4 just below FT8 on each band, with 14.080 MHz named as the standard everyday FT4 frequency on 20 meters and 14.083 MHz suggested during the contest to avoid confusing non-contest stations. Outside contests, FT4 is used for rapid contacts on 20 meters, 15 meters and 10 meters when the band is open and busy.

What a Contest Contact Looks Like

The user guide gives model contacts for each contest. In the North American VHF Contest and the ARRL International Digital Contest, the sequence is a CQ TEST call with callsign and grid, a reply that adds the other station’s callsign and grid, a confirmation that starts with R and repeats the first station’s grid, then RRR or RR73 and, optionally, a final 73. Each message fits into one 7.5-second slot, so the whole exchange needs four transmissions, and with auto-sequencing turned on the program chooses each message for you. In ARRL Field Day the exchange is your class and section, and in FT Roundup it is a signal report and your state, province or DX. The decoder recognizes all these special messages at any time, so you can read contest traffic even when you are not set up for it.

One more rule from the guide is worth remembering: contacts in a contest are generally invalid if they appear in one log and not in the partner’s log. To avoid not-in-log penalties, finish each contact properly, and do not assume that a contact is complete because you sent your last message. Wait for the confirmation, and log only when you have the full exchange from the other side.

Setting Up FT4 in WSJT-X

If FT8 already works on your computer, FT4 needs very little extra. Select FT4 on the Mode menu, and then check the dial frequency: the working frequency table has entries for FT4 on each band, and the band buttons change them automatically. The guide recommends the following wide graph settings for the tutorial: Bins per pixel 5, Start at 100 Hz, N Avg 1, and a window width such that the upper frequency limit is about 3300 Hz. A guide to a first setup is in our article on a WSJT-X FT8 setup that works first time, and the same audio levels apply.

Time accuracy is more important at 7.5 seconds than at 15 seconds, because the same error is a larger fraction of the sequence. Your computer clock must be correct to within a fraction of a second, and our guide to FT8 time synchronization covers the tools that keep it there. Keep ALC action at zero as well, since a signal that is distorted by overdrive is wider than it should be and causes problems for neighbors on a crowded sub-band.

• Frequency steps. Shift+F11 and Shift+F12 move your FT4 transmit frequency down or up in 90 Hz steps, which is just enough to land in the next free slot.
• Alternate F1-F6 bindings. If you enable this on the General tab of the settings, F1 sends CQ and F2 to F5 send the messages in the Tx2 to Tx5 fields, which gives a contest-style keyboard workflow.
• Special operating activity. Choose the contest on the Advanced tab to switch on the correct message format and auto-sequencing.

The Best S+P Button

The FT4 window has a button, labeled Best S+P, which is unique to the mode. Clicking it during a receive cycle arms the program to examine all CQ messages decoded at the end of that sequence. It then selects what it considers the best potential contact, from a contesting perspective, and treats the choice as if you had double-clicked on that line of decoded text. Here best means a new multiplier first, and a new call on the band second. In the current version, a new multiplier means a new DXCC entity.

The button is only useful if you have defined what best means. This is done on the Colors tab of the settings: the selection and order of the color highlighting options decide which stations the button will choose. For the FT Roundup rules, the guide recommends turning on My Call in message, New DXCC, New Call on Band, CQ in message and Transmitted message, in that order from top to bottom. The best way to learn is to practice in a quiet period with the contest activity enabled and see what the program chooses. It is an operator aid, as the guide says about auto-sequencing in general, and it does not replace the operator.

When to Choose FT4 and When to Stay With FT8

FT4 is the right tool in a few clear situations. During a digital contest with strong signals, it doubles the potential rate. On a busy band such as 20 meters in the afternoon, a short cycle gets you through the exchange before propagation changes. On 6 meters during a sporadic E opening, where conditions change quickly and signals can be strong but brief, FT4 lets you complete more contacts before the opening fades. And it is a pleasure to use when you just want a fast contact for a new grid or a country.

FT8 is better in other situations. For weak DX on the low bands, for a marginal path or for a small antenna, the extra 3.5 dB is valuable. FT8 also has far more activity: most people who run digital modes are on FT8, and a CQ in FT4 on a quiet day may bring few replies. For this reason many operators run FT8 as the default and use FT4 only in contests or when they know that others are on it. Our article on FT8 operating etiquette gives the habits that apply equally well to FT4: keep power sensible, avoid transmitting on top of an active contact, and keep your signal clean.

Common Mistakes

The most common FT4 mistake is to run the same audio levels and the same transmit frequency as in FT8 without checking. The signal is wider, and the sub-band for FT4 is not the same as for FT8, so an operator who forgets to change the dial frequency may sit in the wrong place or call over a neighbor. Another mistake is to use FT4 on a band where nobody else is operating it: you will call CQ and receive nothing, and you might conclude that your setup is broken. Check PSK Reporter or listen for a few minutes to see whether there is activity before you decide. Our article on PSK Reporter shows how to see who is hearing you.

A final common problem is the clock. A computer that has drifted by half a second will decode FT8 with only a small loss but may fail on FT4 with a much larger one. If you can decode some stations but not others, check the time offset first, and then the audio level. Both are easy to fix and both account for most reports of poor performance.

The Bottom Line

FT4 is a contest-oriented digital mode that trades a little sensitivity and bandwidth for twice the contact rate of FT8. With a 7.5-second cycle, an occupied bandwidth of 83.3 Hz and a decoding threshold of about -17.5 dB, it works best on strong HF and 6 meter signals, in the contests that have special message formats. Setting it up is a matter of selecting the mode, using the right sub-band and keeping the computer clock accurate. Use FT8 for weak signals and quiet bands, and FT4 when speed matters.

Frequently Asked Questions

What is the difference between FT4 and FT8?

FT4 uses 7.5-second cycles and FT8 uses 15-second cycles. FT4 is about 3.5 dB less sensitive, needs about 1.6 times the bandwidth, and offers the potential for twice the contact rate.

Is FT4 the same as FST4?

No. FST4 is designed for weak-signal contacts on the LF and MF bands, with sequences from 15 seconds to 30 minutes. FT4 is designed for contesting on HF and 6 meters.

Which program do I need?

WSJT-X supports FT4 on the Mode menu, and several compatible programs also support it. The same 77-bit messages are used as in FT8.

What frequency is used for FT4 on 20 meters?

14.080 MHz is the standard everyday FT4 frequency on 20 meters, according to the WW Digi rules, which suggest 14.083 MHz for that contest to avoid confusion with non-contest stations.

What does the Best S+P button do?

It examines all CQ messages decoded in a cycle and chooses the best partner, meaning a new multiplier first and a new call on the band second, as if you had double-clicked that line.

Is FT4 better for DX?

Not usually for weak DX. FT8 is about 3.5 dB more sensitive and has much more activity. FT4 is best when signals are strong and speed matters.