From The RadioReference Wiki
Offset is the difference between a radio channel's receive and transmit frequencies. Most commonly it refers to the separation between the input frequency and output frequency of a repeater or other type of full duplex system. This should not be confused with the trunking offset required when programming certain types of trunked radio systems in certain scanner models.
For example, a mobile radio receives on 146.94 and transmits on 146.34 in order to operate on a repeater.
146.94 - 146.34 = 0.6 (0.6 MHz or 600 kHz)
Since in this case the mobile radio transmit frequency (repeater input) is lower than the mobile radio receive frequency (repeater output), it is said to have a negative offset of 600 kHz or -600 kHz.
Certain bands and frequency ranges in the United States have standardized offsets.
|Band||Frequency Range (MHz)||Offset||Notes|
|10m Ham (repeater subband)||29.5-29.7||-100 kHz|
|VHF Low Band||30-50||No standard offset|
|6m Ham||50-54||-500 kHz or -1 MHz|
|VHF High Band||138-174||No standard offset|
|2m Ham||144-148||+600 kHz or -600 kHz|
|220 MHz||220-222||+1 MHz|
|1.25m Ham||222-225||-1.6 MHz|
|380 MHz Federal LMR||380-400||+10 MHz|
|Federal UHF||406.1-420||+9 MHz|
|70cm Ham (repeater subband)||440-450||+5 MHz or -5 MHz|
|UHF Canadian border area||420-430||+5 MHz|
|UHF T||470-512||+3 MHz|
|Lower 700 MHz||698-746||+30 MHz|
|Upper 700 MHz||746-806||+30 MHz|
|800 MHz||806-896||-45 MHz|
|900 MHz||896-940||-39 MHz|
|33cm Ham||902-928||-12 MHz or -25 MHz|
|23cm Ham||1240-1300||-12 MHz or -20 MHz|
- 1. Ham radio offsets can vary in certain areas of the country. Some repeaters in some areas may use non standard offsets and are commonly referred to as odd split repeaters.
- 2. There are some paired channels in the VHF high band (marine VHF, paging, taxi, old RCC mobile phone channels) but no standard offset.
- 3. The 406.1-420 MHz federal land mobile band began changing to a +9 MHz offset a few years ago. Many older systems remain with non-standard offsets.
- 4. The UHF T band is only available in certain areas. See Note 1 at Television Frequencies.
- 5. The middle part (716-728 MHz) of the Lower 700 MHz band is unpaired.
- 6. Conventional and trunked repeaters between 935-940 MHz have a -39 MHz offset. There are other paired channels (paging, PCS and Part 101 microwave) with different offsets in the 896-960 MHz band, and unpaired channels.
Related Wiki Articles
- 220-222 MHz Band Plan
- 700 MHz Public Safety Band Plan
- 900 MHz LMR Band Plan
- Amateur Radio
- Federal VHF/UHF Channel Plans
- 700MHzBandPlan.pdf - Revised 700 MHz Band Plan for Commercial Services (FCC web site)