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Offset

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Revision as of 13:12, 16 August 2015 by QDP2012 (talk | contribs) (updated categories)

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 = 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.

Standart US 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 LM 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
700 MHz 746-806 +30 MHz
800 MHz 806-896 -45 MHz
900 MHz 896-940 -39 MHz 4
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. There are other paired channels (paging, PCS and Part 101 microwave) with different offsets in the 896-960 MHz band.


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