You program a repeater into your radio, key up, and... nothing comes back. Or the repeater opens but nobody hears you. Nine times out of ten, the culprit is a CTCSS tone — either missing, wrong, or programmed backwards. Here's exactly what CTCSS is, why it matters, and how to get it right the first time.
What Is CTCSS?
CTCSS stands for Continuous Tone-Coded Squelch System. It's a sub-audible tone — between 67.0 and 254.1 Hz — transmitted simultaneously with your voice signal. The repeater's receiver is configured to only open (activate the transmitter) when it detects the specific tone it's programmed to require. Without the correct tone, your signal reaches the repeater but the repeater ignores it and stays silent.
You won't hear the CTCSS tone during normal listening — it's filtered out before reaching the speaker. But it's there in the transmitted signal, riding below the voice audio.
Why repeaters use CTCSS: Repeaters sit on hilltops and have excellent receive sensitivity. Without tone squelch, a distant interfering signal, a commercial radio bleed-over, or even electrical noise could trigger the repeater constantly. CTCSS lets the trustee filter for intentional local users while ignoring everything else.
CTCSS vs. DCS: What's the Difference?
DCS (Digital-Coded Squelch), also called CDCSS, does the same job as CTCSS but uses a digital data burst instead of an analog tone. DCS codes are three-digit numbers (like 023, 114, 156) rather than frequencies. Your radio programs them the same way — just select DCS mode instead of CTCSS (Tone) mode and enter the code. Most modern repeaters use one or the other, rarely both.
Some older hams still call CTCSS by its Motorola trade name: PL tone (Private Line). If someone says "you need PL 100," they mean CTCSS 100.0 Hz.
Standard Repeater Offsets
Along with the tone, every repeater uses a frequency offset — the difference between the input frequency (what you transmit on) and the output frequency (what the repeater transmits on, and what you listen on). Your radio needs to know this offset to automatically use the right transmit frequency when you tune to a repeater's output.
| Band | Standard Offset | Direction | Example |
|---|---|---|---|
| 6m | 1.0 MHz | Minus (–) | Output 52.525 / Input 51.525 |
| 2m | 600 kHz | Minus (–) | Output 146.880 / Input 146.280 |
| 2m | 600 kHz | Plus (+) | Output 146.040 / Input 146.640 |
| 1.25m | 1.6 MHz | Minus (–) | Output 224.500 / Input 222.900 |
| 70cm | 5.0 MHz | Minus (–) | Output 447.000 / Input 442.000 |
| 70cm | 5.0 MHz | Plus (+) | Output 442.500 / Input 447.500 |
| 33cm | 12.0 MHz | Minus (–) | Output 927.000 / Input 915.000 |
The 2m band splits at 147.000 MHz: repeaters below that frequency generally use a + offset; above it, a – offset. Many radios auto-set the offset when you tune to a standard repeater frequency — but always verify with the repeater directory.
Complete CTCSS Tone Reference
| Tone (Hz) | Tone (Hz) | Tone (Hz) | Tone (Hz) |
|---|---|---|---|
| 67.0 | 100.0 | 141.3 | 203.5 |
| 69.3 | 103.5 | 146.2 | 210.7 |
| 71.9 | 107.2 | 151.4 | 218.1 |
| 74.4 | 110.9 | 156.7 | 225.7 |
| 77.0 | 114.8 | 162.2 | 233.6 |
| 79.7 | 118.8 | 167.9 | 241.8 |
| 82.5 | 123.0 | 173.8 | 250.3 |
| 85.4 | 127.3 | 179.9 | 254.1 |
| 88.5 | 131.8 | 186.2 | — |
| 91.5 | 136.5 | 192.8 | — |
| 94.8 | — | 199.5 | — |
| 97.4 | — | — | — |
The most commonly used tones are 100.0, 103.5, 107.2, 110.9, 123.0, 127.3, 136.5, and 141.3 Hz. If you're not sure which tone a repeater uses, check RepeaterBook.com — it lists tone information for virtually every active repeater in North America.
How to Find a Repeater's Tone
- RepeaterBook.com — Search by frequency or ZIP code. Listings include output frequency, offset, tone type (CTCSS/DCS), and tone value.
- Your local club's website — Club-sponsored repeaters often list their information on the club's web page.
- The ARRL Repeater Directory — Updated annually in print; less convenient than RepeaterBook but authoritative.
- Scan mode with tone search — Most modern radios have a CTCSS scan function that detects what tone a transmitting station is using. Tune to the repeater output frequency, listen for a transmission, and run tone search.
Programming Into Your Radio: The Settings You Need
To access a tone-protected repeater, you need three things set correctly in your radio's memory channel:
- Output frequency — The frequency you listen on (and that displays on the radio)
- Offset direction and amount — Usually programmed as +600 kHz or –600 kHz on 2m; ±5.0 MHz on 70cm
- CTCSS encode tone — The tone you transmit. Set this to the repeater's required tone. This is sometimes labeled "Tx Tone," "Enc Tone," or just "Tone" in your radio's menus.
Note: You usually do not need to set a CTCSS decode tone (sometimes called "Rx Tone" or "Tone Squelch") unless you want your radio's squelch to only open when the repeater is transmitting the same tone back to you — a useful feature to reduce noise from distant repeaters on the same frequency.
Using CHIRP to program repeaters: If you have a Baofeng, Yaesu FT-65, or many other radios, the free CHIRP software (chirpmyradio.com) can import entire repeater lists from RepeaterBook automatically. Search your ZIP code in RepeaterBook → export CSV → import into CHIRP → upload to radio. 50 local repeaters programmed correctly in under 10 minutes.
Troubleshooting: Why You Can't Access the Repeater
- No CTCSS tone set — Most common issue. Check that you've enabled Tone Encode mode (not just Tone Squelch)
- Wrong tone value — Verify against RepeaterBook. 100.0 and 100 Hz are the same; 110.9 and 110 Hz are not
- Wrong offset direction — If you're on 147.100, you need a + offset; on 146.880 you need –. Check your radio's offset direction setting
- Not enough power or antenna — A rubber duck antenna on a handheld has real limitations. Try a mobile mag-mount antenna if handheld range is poor
- Repeater is down or requires a net control to activate — Some club repeaters are linked or controlled systems that only activate during nets