Difference between revisions of "Offset"
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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. | 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. | ||
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− | 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 = .6 (.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. | + | 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 = .6 (.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. |
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Revision as of 02:54, 6 June 2010
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.
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 = .6 (.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 fixed offsets.
Band | Frequency Range | Offset | Notes |
---|---|---|---|
10m Ham | 29.5-29.7 | -100 kHz | |
VHF Low Band | 30-50 | No standard offset | |
6m Ham | 50-54 | -500 kHz or -1 MHz | 1 |
2m Ham | 144-148 | +600 kHz or -600 kHz | |
VHF High Band | 138-174 | No standard offset | 2 |
220 MHz | 220-222 | +1 MHz | |
1.25m Ham | 222-225 | -1.6 MHz | |
380 MHz | 380-400 | +10 MHz | |
Federal UHF | 406.1-420 | +9 MHz | 3 |
70 cm Ham | 420-450 | +5 MHz or -5 MHz | 1 |
UHF | 450-470 | +5 MHz | |
UHF T | 470-512 | +3 MHz | |
700 MHz | 769-806 | +30 MHz | |
800 MHz | 806-896 | -45 MHz | |
900 MHz | 896-940 | -39 MHz | |
1.2 GHz Ham | 1240-1300 | -20 MHz or -12 MHz | 2 |
Notes
- 1. Ham radio offsets can vary in certain areas of the country.
- 2. There are some paired channels in the VHF high band (paging, taxi, old RCC mobile phone channels) but not standard offset.
- 3. The 406.1-420 federal land mobile band began changing to a +9 MHz offset a few years ago. Some older systems still remain with non-standard offsets.