Offset

Offset (sometimes referred to as 'split') 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 MHz and transmits on 146.34 MHz 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. Amateur radio repeater offsets can vary. Some repeaters 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 changed to a +9 MHz offset as of 2008, but older systems remain with non-standard offsets.
• 4. The UHF-T band is only available in certain areas. See UHF-T Band.
• 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.

Related Wiki Articles

• 220-222 MHz Band Plan
• 700 MHz Public Safety Band Plan
• 900 MHz LMR Band Plan
• Amateur Radio
• Federal VHF/UHF Channel Plans

Related Links

• 700MHzBandPlan.pdf - Revised 700 MHz Band Plan for Commercial Services (FCC web site)