FT8 on CB Channel 26

FT8 has taken over Channel 26 USB (27.265 MHz) as an incredibly efficient way to rack up 11-metre DX contacts on the CB band. It remains effective even when solar propagation drops or conditions are noisy.

No Specialized Hardware Required (Acoustic Coupling)

You do not need an expensive CAT control interface, complex sound card wiring, or specialized gear to get on the air. You can operate FT8 reasonably well through acoustic coupling—simply letting your radio and smart device talk to each other through their built-in microphones and speakers.

Setup: Set your CB to Channel 26 USB and place your smartphone or laptop directly next to the radio's speaker and microphone. 

Receiving: Turn the squelch completely off, turn the RF gain up, and let your device's microphone listen to the radio's speaker to decode the incoming FT8 tones.

Transmitting: When the 15-second FT8 cycle begins, manually press the PTT button on your CB mic. Hold your device's speaker close to the CB microphone and let the transmit tones play, using the minimum volume necessary to achieve maximum power output on your radio. Release the PTT when the 12.6-second tone burst finishes. 

Pro-Tip: For clean, undistorted data tones, keep ambient room noise down (like TVs or fans) and disable any audio processing on your radio, such as Echo/Talkback or Mic Gain boosts.

The Problem with Standard CB Call Signs

A significant issue arises when using traditional CB "division number" handles (like 14USB001 or 30FAT123) with standard FT8 apps or unmodified software like WSJT-X. Because the native 28-bit compression algorithm cannot process these standard CB formats, the software is forced to send the call sign literally, character by character. This full-text transmission consumes nearly the entire data payload, swallowing the space required to include a Maidenhead grid locator or a second call sign. To try and make room for signal reports in subsequent messages, the software resorts to a 12-bit hash (which causes the call sign to appear in <brackets>). However, if the receiving station misses the initial full-text broadcast, they cannot decode the hashed abbreviation, causing dropped decodes and failed contacts.

(A quick back-of-the-envelope calculation shows that a division-club-member number handle could theoretically be encoded in 28 bits only if a maximum of two club letters and 1000 members are allowed.)

Current Solutions

To bypass this limitation, many operators turn to modified versions of WSJT-X, such as WSJT-CB, designed specifically to accommodate standard CB handles. However, using modified software is not strictly necessary.

Using Standard FT8 Software Efficiently

You can use regular, unmodified FT8 software (WSJT-X, JTDX, FT8CN, FT8TW, etc.) simply by adopting a custom call sign that perfectly fits the 28-bit mathematical structure while ensuring it is not a valid, ITU-compliant amateur radio call sign, or a non-compliant call sign used by licensed amateur radio operators.

Call signs that the FT8 protocol sends efficiently

The call signs that are sent as a compact 28-bit word have this form:

• A prefix, which can be a single letter, a letter followed by a digit, or a digit followed by a letter
• The separator, a single digit.
• The suffix, made up of one, two or three letters.

Not all call signs efficiently encoded by FT8 are compliant call signs

According to ITU Radio Regulations, volume 1, chapter 5, article 19, single-letter prefixes have to be one of these: B, F, G, I, K, M, N, R, and W. The remaining single-letter prefixes are in principle available.

Also, to prevent global identification errors, the ITU generally categorizes any prefix containing a 0 or a 1 (such as 0X, 1X, X0, or X1) as "unavailable". Some hams, however, use “unavailable” prefixes such as S0 (“Western Sahara”), 1A (“Sovereign Order of Malta”), 1B (“Turkish Republic of Cyprus”). Also, there are countries that issue non-conformant call signs with a number-letter prefix but no separating digit (such as E7DX where E7=Bosnia and Herzegovina or C4R where C4=Cyprus).

Which call signs to use, then?

It’s hard to guarantee a call sign with is not used by licensed hams, but one could start by selecting:

• Prefix: 
• A 0 or a 1 followed by a letter
• A letter followed by a 0 or a 1
• A single letter which is not B, F, G, I, K, M, N, R, or W.
• Separator: Exactly one single digit (0 through 9).
• Suffix: One to three letters, restricted to A–Z only, with absolutely no trailing numbers.

One should then check (for instance, in QRZ.com) to try and avoid call signs used by licensed hams. 

Call signs starting with zero, of the form 

    (0) + (letter) + (digit) + (one, two, or three letters) 

are quite unlikely to be in use by hams.

By using 28-bit-ready formats like 0L1VES, 1D1OM, or Y0UNG, your call sign avoids the hashing problem entirely and even looks good. Of course, call signs do not have to “make sense”: you can use random combinations like 0K7FNZ, as long as they adhere to the rules. When both you and your contact use 28-bit compliant call signs, standard software will transmit full grid locators and signal reports instantly in a single frame, with zero lost data.