The Offset — Why Repeaters Need It
A repeater simultaneously listens on one frequency (input) and transmits on another (output). When you key up, your radio needs to transmit on the input while you listen on the output. The difference between input and output is the offset. You program the output frequency (what you tune to) and tell the radio the offset amount and direction. The radio handles the switching automatically when you PTT.
Standard Offsets by Band
| Band | Standard Offset | Typical Direction | Example |
|---|---|---|---|
| 2 meters (144 MHz) | 600 kHz (0.600 MHz) | + (transmit higher) | Output 147.195, transmit 147.795 |
| 1.25 meters (222 MHz) | 1.6 MHz | − (transmit lower) | Output 224.200, transmit 222.600 |
| 70 cm (440 MHz) | 5 MHz | + (transmit higher) | Output 442.100, transmit 447.100 |
Most repeaters follow the standard, but not all. Always verify direction on RepeaterBook.com for your specific repeater — some use "reverse splits" or non-standard offsets.
CTCSS — The Sub-Audible Access Tone
CTCSS (Continuous Tone-Coded Squelch System), also called PL tone (Motorola's "Private Line" trademark), is a sub-audible tone below human hearing range transmitted alongside your voice. The repeater ignores signals that do not carry the correct tone — this prevents accidental activation by distant interference or other radio services on the same frequency.
CTCSS tones range from 67.0 Hz to 254.1 Hz and are listed on RepeaterBook for each repeater. The tone is set in your radio as a transmit-only tone for that memory channel.
Setting Offset and CTCSS in CHIRP
In CHIRP (the free programming software for Baofeng and many other radios):
- Frequency: Enter the repeater's output frequency (e.g., 147.195)
- Duplex: Set to "+" or "−" depending on offset direction
- Offset: Enter 0.600 for 2m, 5.000 for 70cm
- Tone Mode: Set to "Tone" (transmit tone only — most common)
- CTCSS: Enter the tone frequency from RepeaterBook (e.g., 100.0)
Tone vs. TSQL: "Tone" means your radio sends the CTCSS tone when transmitting. "TSQL" means your radio also requires receiving that tone to unmute the speaker. For repeater use, "Tone" is correct — you want to hear all repeater output, not just transmissions with your CTCSS tone.
- What if the repeater does not respond even with the correct tone?Verify both the tone frequency and the offset direction on RepeaterBook. Common mistake: entering the right tone value but the wrong offset direction (+ vs −). Also check that the tone is set to "Tone" mode, not "None" or "TSQL." If everything seems correct but the repeater still does not respond, the repeater may be offline or the entry on RepeaterBook may be outdated.
- What is DCS and how is it different from CTCSS?DCS (Digital Coded Squelch) is an alternative to CTCSS that uses a digital data stream rather than an analog tone. Some repeaters use DCS instead of CTCSS. RepeaterBook lists DCS codes separately. In CHIRP, set Tone Mode to "DTCS" and enter the DCS code number in the DTCS field. DCS and CTCSS are not interchangeable — use whichever the repeater requires.
Informational only. Verify current rules at fcc.gov and arrl.org. Not affiliated with the FCC, ARRL, or any VEC.