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Offset


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.

Standart US Offsets
Band Frequency Range (MHz) OffsetNotes
10m Ham (repeater subband)29.5-29.7-100 kHz1
VHF Low Band30-50No standard offset
6m Ham50-54-500 kHz or -1 MHz1
VHF High Band138-174No standard offset2
2m Ham144-148+600 kHz or -600 kHz1
220 MHz220-222+1 MHz
1.25m Ham222-225-1.6 MHz1
380 MHz Federal LMR380-400+10 MHz
Federal UHF406.1-420+9 MHz3
70cm Ham (repeater subband)440-450+5 MHz or -5 MHz1
UHF Canadian border area420-430+5 MHz
UHF450-470+5 MHz
UHF T470-512+3 MHz4
Lower 700 MHz698-746+30 MHz5
Upper 700 MHz746-806+30 MHz
800 MHz806-896-45 MHz
900 MHz896-940-39 MHz6
33cm Ham902-928-12 MHz or -25 MHz1
23cm Ham1240-1300-12 MHz or -20 MHz1

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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