Repeater Offsets and CTCSS Tone Chart

A repeater will not answer you unless four things are right: the output frequency, the offset direction, the offset size and the access tone. Get any one wrong and the machine is silent, which is indistinguishable from a broken radio and is the single most common false fault report in amateur radio. This page has the standard values for all of them.

Standard offsets by band

The offset is the difference between the repeater's output frequency, which is what you listen to, and its input frequency, which is what you transmit on. A repeater with an output of 146.940 MHz and a minus 600 kHz offset listens on 146.340 MHz. Your radio handles the arithmetic once the offset is programmed; you enter the output frequency and the offset direction.

The plus and minus rule of thumb on 2 metres is that outputs below 147.000 MHz generally use a minus offset and those above it generally use a plus. It is right often enough to be worth knowing and wrong often enough that you should check a directory. On 70 centimetres the offset is plus almost everywhere in the United States, though regional coordinators do vary this.

The CTCSS tone set

Continuous tone-coded squelch system, universally shortened to CTCSS and sometimes called by the trade name PL, transmits a low-frequency tone below the audio passband alongside your voice. The repeater listens for the correct tone before it opens. The standard set is 39 tones, and every amateur radio made in the last thirty years has all of them.

The tones cluster closely at the low end and spread out higher up, which is deliberate: the spacing is designed so that a receiver decoding one tone does not false-trigger on an adjacent one. That is also why you cannot invent a tone. Using 105.0 Hz because it sits between two standard values will simply not open anything.

Programming software presents three related settings and confusing them is common:

• Tone or encode. Your radio transmits the tone. This is what opens the repeater and it is what you need. Set this and nothing else if you are unsure.
• TSQL or tone squelch. Your radio transmits the tone and also stays silent unless it hears a matching tone on receive. Useful on a busy or noisy frequency, and it will make the radio appear deaf if the repeater does not transmit a tone.
• Cross tone. Different tones for transmit and receive. Occasionally needed on linked systems and almost never otherwise.

DCS, the digital alternative

Digital coded squelch sends a continuous low-speed digital code rather than a tone. It does the same job, offers far more unique codes, and rejects interference marginally better. Repeaters use one system or the other and never both at once.

DCS codes are written as three octal digits, which is why the numbers look odd: 023, 025, 026, 031, 032, 043, 047, 051, 054, 065, 071, 072, 073, 074, 114, 115, 116, 122, 125, 131, 132, 134, 143, 152, 155, 156, 162, 165, 172, 174, 205, 223, 226, 243, 244, 245, 251, 261, 263, 265, 271, 306, 311, 315, 331, 343, 346, 351, 364, 365, 371, 411, 412, 413, 423, 431, 432, 445, 464, 465, 466, 503, 506, 516, 532, 546, 565, 606, 612, 624, 627, 631, 632, 654, 662, 664, 703, 712, 723, 731, 732, 734, 743 and 754. Each also has an inverted form, which programming software shows as an N or an I suffix.

In practice you look the code up in a repeater directory and enter it exactly as printed. There is no equivalent of the CTCSS tone chart worth memorising.

Simplex calling frequencies

Simplex means transmitting and receiving on the same frequency with no repeater involved, which is what you do when the other station is close enough. A calling frequency is for establishing contact and then moving, in exactly the way a marine or aviation calling channel works. Holding a twenty minute conversation on 146.520 MHz is the VHF equivalent of parking in a loading bay.

Simplex is worth practising because it is the mode that still works when the repeater is off the air, which is precisely the situation emergency communication groups train for. Two handhelds at head height reach one to two miles in suburban terrain, and considerably further from high ground. The arithmetic is on the VHF range calculator.

When the repeater will not answer

Work through this list in order. The fault is almost never the radio.

1. Check the offset direction. Plus where it should be minus is the most common single error. Your radio should show a plus or minus indicator when you key up.
2. Check the offset size. A radio set to 600 kHz on a 70 centimetre repeater is transmitting 4.4 MHz away from the input.
3. Check the tone. Both the value and that it is set to encode rather than off. This is the second most common error.
4. Check you are not on tone squelch by accident. If the radio is silent but the repeater is busy, you have TSQL set with the wrong receive tone.
5. Listen for the repeater's own identification. If you cannot hear the machine at all, none of the above matters and the problem is range or the frequency.
6. Go outside and stand up. Free, instant, and frequently worth more than any equipment change. Buildings attenuate VHF badly.
7. Fit a better antenna. A Nagoya NA-771C 15-inch whip$15.98 in place of the stock rubber duck is worth 2 to 3 dB on transmit and receive for about sixteen dollars.
8. Check the repeater is actually on the air. Directories list machines that have been dead for years. Ask on a local net.

Programming this into a radio

Entering one repeater by keypad means navigating an unlabelled menu system to set a receive frequency, an offset direction, an offset size, a transmit tone and a memory name. Entering fifty means doing that fifty times, which is why almost nobody does it twice.

The free CHIRP software plus a genuine BTECH PC03 FTDI programming cable$22.49 cable loads fifty repeaters in two minutes from a spreadsheet view. The cable must have a genuine FTDI chip; counterfeit serial chips are the single most common reason CHIRP will not connect. Radios that programme from a phone over Bluetooth, such as the BTECH UV-PRO$164.89 and the TIDRADIO TD-H8$129.99, remove the cable from the equation entirely, which is the biggest usability improvement in the budget handheld category.

The step by step walkthrough, including the column names CHIRP uses for each of these settings, is on programming a Baofeng with CHIRP.

What to programme first

• The two or three local repeaters that actually have people on them, in the lowest memory channels.
• The repeater your local club's weekly net runs on, which is the easiest possible first contact.
• The 2 metre and 70 centimetre simplex calling frequencies.
• Two or three simplex working frequencies to move to after a contact.
• The NOAA weather channels, which are receive only and need no license.
• Any repeater with a wide-area linked system, which is often the one that works from the car.

Ask the club that ran your exam session which repeaters are busy rather than programming everything in the directory. A directory lists machines; it does not tell you which ones have anyone listening, and a radio full of dead repeaters is how people conclude the hobby is quiet. More on that in what to do after you pass.