Offset
From The RadioReference Wiki
Offset is the difference between receive and transmit frequencies of a radio channel. 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 scanners.
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 transmit frequency is lower than the receive frequency, 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 | 1 |
VHF Low Band | 30-50 | No standard offset | |
6m Ham | 50-54 | -500 kHz or -1 MHz | 1 |
VHF High Band | 138-174 | No standard offset | 2 |
2m Ham | 144-148 | +600 kHz or -600 kHz | 1 |
220 MHz | 220-222 | +1 MHz | |
1.25m Ham | 222-225 | -1.6 MHz | 1 |
380 MHz Federal LMR | 380-400 | +10 MHz | |
Federal UHF | 406.1-420 | +9 MHz | 3 |
70cm Ham (repeater subband) | 440-450 | +5 MHz or -5 MHz | 1 |
UHF Canadian border area | 420-430 | +5 MHz | |
UHF | 450-470 | +5 MHz | |
UHF T | 470-512 | +3 MHz | 4 |
Lower 700 MHz | 698-746 | +30 MHz | 5 |
Upper 700 MHz | 746-806 | +30 MHz | |
800 MHz | 806-896 | -45 MHz | |
900 MHz | 896-940 | -39 MHz | 6 |
33cm Ham | 902-928 | -12 MHz or -25 MHz | 1 |
23cm Ham | 1240-1300 | -12 MHz or -20 MHz | 1 |
Notes
- 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
Related Links
- 700MHzBandPlan.pdf - Revised 700 MHz Band Plan for Commercial Services (FCC web site)