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Offset


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 standardized offsets.

Standart US Offsets
BandFrequency RangeOffsetNotes
10m Ham (repeater subband)29.5-29.7-100 kHz
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 MHz
380 MHz Federal LM380-400+10 MHz
Federal UHF406.1-420+9 MHz3
70cm Ham420-450+5 MHz or -5 MHz1
UHF Canadian border area420-430+5 MHz
UHF450-470+5 MHz
UHF T470-512+3 MHz
700 MHz746-806+30 MHz
800 MHz806-896-45 MHz
33cm Ham902-928-12 MHz or -25 MHz1
900 MHz935-940-39 MHz4
23cm Ham1240-1300-12 MHz or -20 MHz1

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 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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