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Offset

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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.

Standard 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 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.


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