Repeater Offset Calculator
Created by: James Porter
Last updated:
Enter a repeater output frequency and instantly get the correct input frequency to program into your radio, with standard band offset auto-detection for 6m through 23cm.
Repeater Offset Calculator
Amateur RadioCalculate repeater input and output frequencies from the standard or custom offset. Auto-detects the standard offset for VHF/UHF amateur radio bands.
Note: These results are for guidance only and shouldn't be taken as professional advice. Always double-check with a qualified expert before making decisions.
What is a Repeater Offset Calculator?
A repeater offset is the frequency difference between a repeater's output (the frequency you listen on) and its input (the frequency you transmit on). Because a repeater receives and retransmits simultaneously, its transmitter and receiver must operate on different frequencies to prevent the outgoing signal from completely overwhelming the incoming one. The amount and direction of that separation is called the offset, and it is standardized for each amateur radio band so that all operators know which transmit frequency to use without having to look up each repeater individually.
Standard offsets are set by regional frequency coordinators and ARRL recommendations rather than by FCC rule — Part 97.205 authorizes repeater operation but leaves offset values to coordination bodies. On 2 meters (144–148 MHz), the standard offset is ±600 kHz, with the direction depending on the output frequency: minus 600 kHz below 147 MHz and plus 600 kHz above 147 MHz. On 70 centimeters (420–450 MHz), the US standard is +5 MHz, meaning the repeater's input is 5 MHz above its output. On 6 meters, the offset is ±1 MHz; on 1.25 meters, −1.6 MHz; on 33 centimeters, −25 MHz; and on 23 centimeters, −20 MHz.
CTCSS (Continuous Tone-Coded Squelch System), trademarked as "Private Line" or PL by Motorola, is a sub-audible tone between 67 and 254.1 Hz that a radio encodes below its voice audio. Most repeaters require the correct CTCSS tone to open their squelch, preventing the repeater from activating on adjacent-channel interference or distant co-channel signals. When you program a repeater memory channel, you configure the receive frequency, transmit frequency (derived from the offset), and the encode tone. You rarely need to decode CTCSS on the receive side for repeater operation.
Knowing your repeater's correct input frequency and CTCSS tone is essential for practical VHF and UHF operation. Entering the wrong transmit frequency can cause interference to another repeater pair or fail to reach the target repeater entirely. This calculator auto-detects the standard offset for any frequency you enter in a recognized band, shows the exact TX and RX frequencies to program into your radio's memory, and flags non-standard offsets so you know to double-check with the local repeater directory before transmitting.
How the Repeater Offset Calculator Works
The calculator begins by checking which amateur band your entered output frequency falls in. It compares the frequency against stored band boundaries for 6m, 2m, 1.25m, 70cm, 33cm, and 23cm. Once a band match is found, it applies the standard offset magnitude for that band. For 2 meters, it also applies the frequency-dependent direction rule: outputs below 147 MHz use a minus offset, outputs at or above 147 MHz use a plus offset.
The transmit (input) frequency is computed as TX = output + (direction × offset), where direction is −1 for a minus offset and +1 for a plus offset. If you have entered a custom override offset, that value takes priority and you control the direction manually. The result is displayed to four decimal places (10 Hz resolution) to match the programming precision of most modern transceivers and memory managers. A standard-offset indicator shows whether the result is a coordinated pair or a non-standard configuration.
Repeater offset formulas
TX_freq = output_freq + (direction × offset)
direction = −1 for minus offset, +1 for plus offset
2m: offset = 0.600 MHz; direction = −1 if output < 147 MHz, +1 if ≥ 147 MHz
70cm: offset = 5.000 MHz; direction = +1 (US standard)
6m: offset = 1.000 MHz; direction = −1 (US standard)
1.25m: offset = 1.600 MHz; direction = −1
33cm: offset = 25.000 MHz; direction = −1
23cm: offset = 20.000 MHz; direction = −1
Example Calculations
2m repeater, output 146.940 MHz
Output = 146.940 MHz (below 147 MHz → minus offset). TX = 146.940 + (−1 × 0.600) = 146.340 MHz. Program receive: 146.940 MHz, transmit: 146.340 MHz. CTCSS encode: per local directory (commonly 100.0 Hz in many US areas).
70cm repeater, output 442.100 MHz
Output = 442.100 MHz (70cm band → +5 MHz offset). TX = 442.100 + (+1 × 5.000) = 447.100 MHz. Program receive: 442.100 MHz, transmit: 447.100 MHz. This +5 MHz positive offset is the US standard for 70cm and differs from the 2m minus convention.
2m repeater, output 147.195 MHz (above 147 MHz)
Output = 147.195 MHz (above 147 MHz → plus offset). TX = 147.195 + (+1 × 0.600) = 147.795 MHz. Program receive: 147.195 MHz, transmit: 147.795 MHz. Note that this is a plus offset because the output is above 147.000 MHz — a common source of confusion for new operators.
Common Amateur Radio Uses
- Programming memory channels in HTs and mobile radios for local repeater access
- Verifying repeater input/output pairs from a printed or online repeater directory
- EmComm and ARES net setup where precise frequency programming is critical
- Identifying non-standard offset repeaters that require manual offset entry
- Ham radio licensing study — understanding duplex operation and frequency coordination
- Cross-border operation where regional offset conventions may differ from home area
Tips for Better Ham Radio Planning
Always verify the CTCSS tone from the ARRL Repeater Directory, RepeaterBook, or a local club's frequency list before transmitting. The calculator displays the tone you enter as a reference, but tones are not standardized — each repeater trustee sets their own access tone. Some repeaters use DCS (Digital-Coded Squelch) codes instead of analog CTCSS; your radio's memory should offer both options.
If you receive audio from a repeater but your transmissions don't key it up, check three things in order: correct offset direction (plus vs. minus), correct CTCSS/DCS tone, and adequate RF power to reach the input site. Many 70cm repeater inputs are located at high-elevation sites and may need more than 5 watts from a handheld. If possible, listen for other stations making contacts and confirm your offset is correct by monitoring the input frequency directly.
When visiting a new area, download the local frequency coordination organization's repeater list in addition to checking RepeaterBook. Some coordinated repeaters are not in national databases, and the offset or tone may differ from what online sources show. Regional ARRL Section frequency coordinators maintain the authoritative lists for their areas.
Frequently Asked Questions
What is a repeater offset?
A repeater simultaneously receives on one frequency (the input) and retransmits on another (the output) to extend coverage. The difference between these two frequencies is the offset. When you talk through a repeater, your radio transmits on the repeater's input and listens on the repeater's output. Standard offsets are coordinated by frequency coordinators for each band to prevent interference between repeater pairs.
What are the standard repeater offsets for each band?
6m: ±1 MHz. 2m: −600 kHz (below 147 MHz) or +600 kHz (above 147 MHz). 1.25m: −1.6 MHz. 70cm: +5 MHz in most of the USA (−5 MHz in some areas — check local coordination). 33cm: −25 MHz. 23cm: −20 MHz. Non-standard offsets exist on some repeaters; check a local repeater directory.
What is CTCSS / PL tone?
Continuous Tone-Coded Squelch System (CTCSS), trademarked as "Private Line" (PL) by Motorola, is a sub-audible tone (67–254.1 Hz) transmitted below the voice audio. A repeater with CTCSS tone access only opens its receiver squelch when it detects the correct tone. This prevents the repeater from keying up on interference or other repeaters. You must program your radio to encode (transmit) the correct tone; you typically do not need to decode it.
How do I program a split memory channel on my radio?
Most HTs and mobile radios have a split (duplex) memory mode. Enter the receive (output) frequency, then set the offset amount and direction, and your radio calculates the transmit frequency automatically. Alternatively, on radios that require manual entry, program the TX frequency separately. Consult your radio's manual for the specific steps. Many radios auto-detect the standard offset when you enter a frequency in a known band.
Why is the 70cm offset +5 MHz rather than −5 MHz?
In most of the US, 70cm repeater inputs are 5 MHz above the output (i.e., a positive offset). This convention was established by frequency coordinators and differs from the minus convention used on 2m. In some US regions and internationally, −5 MHz is used. Always verify the correct offset with the local repeater directory or coordination organization before transmitting.
Can I use a non-standard offset?
Yes — enter the actual offset in the "Override Offset" field along with the direction. Non-standard offsets appear on some repeaters due to frequency coordination constraints, split-site linking, or legacy installations. The calculator will flag the entry as non-standard so you know to verify before transmitting.
Sources and References
- ARRL Handbook (latest edition) — Chapter on VHF/UHF Repeater Systems
- FCC Part 97.205 — Repeater Station Authorization and Operation
- ARRL Repeater Directory (annual) — North American coordinated repeater listings
- TAPR Frequency Coordination Guidelines — Offset and channel separation standards
- IARU Region 2 Band Plan — VHF/UHF frequency use recommendations for the Americas