Frequency offset

Short description: Intentional frequency shift in broadcasting

In radio engineering, a frequency offset is an intentional slight shift of the broadcast radio frequency (RF), to reduce interference with other transmitters.[1][2] Carrier frequency offset arises from mismatches between the received signal's carrier frequency and the receiver's local oscillator, often due to synchronization errors and Doppler shifts.[3]

## Contents

* 1 Interference
* 2 The shift in RF
* 3 Example
* 4 References

## Interference

The most important problem encountered in broadcasting via terrestrial transmitters is the interference from other broadcasters. In principle, each broadcaster has a different radio frequency (planned by the public authority) in a common reception area to avoid interference from each other. However, there are still two problems: spurious radiation of adjacent channels and fringe reception.[1][2]

Fringe reception is unintended reception under certain weather conditions. The exceptionally long-range reception means that the receiver may be tuned to more than one transmitter (transmitting at same frequency) at the same time. These transmitters may transmit programs of different broadcasters as well as the programs of the same broadcaster. In analogue transmission, even the transmitters transmitting the very same program interfere each other because of phase differences of the incoming signal, but in digital transmission the transmitters transmitting the same program in the same channel may reinforce each other.[1][2]

## The shift in RF

In order to reduce the interference from the fringe area transmitters transmitting in the same channels, a method named frequency offset is often used. By this method, a slightly shifted RF is assigned for a transmitter which may experience interference from other transmitters.

In TV transmission, the shifted RF is calculated by the formula;

fos=fch+fL⋅p12

where,

fos is the offset RF,
fch is the standard channel frequency,
p is an integer such that −12<p<0 or 0>p>12
fL is the line frequency. (15625 Hz. for 625-line systems, 15750 Hz. for System M and System J and 20475 Hz. for system E)

Precision offset is the same as frequency offset, except that in this case, the offset frequency is produced by a cesium controlled oscillator.

## Example

8p offset of channel 9 in system B can be found readily

The standard visual carrier frequency is 203.25 MHz The line frequency is 15.625 Hz.

fos=203250000+15626⋅812≈203260417

8n offset of the same channel is likewise

fos=203250000−15626⋅812≈203239583

## References

1. ↑ 1.0 1.1 1.2 "What are Frequency Offset and Clock Slips? How to measure Clock Slips" (in en). https://kb.veexinc.com/en/knowledge/what-are-frequency-offset-and-clock-slips.
2. ↑ 2.0 2.1 2.2 "Frequency Offset Mode". https://helpfiles.keysight.com/csg/N52xxB/FreqOffset/Frequency_Offset_Mode.htm.
3. ↑ Kotb, Moatasem Mohammed Elsayed; Mohamed, Maha Raof Abdel-Haleem; Fahmy, Ashraf Yahya Hassan Ali; Mohra, Ashraf Shawky Selim SayedAhmed (2025-05-05). "Fine carrier frequency offset estimation for OFDM and MIMO-OFDM systems: A comparative study". Scientific Reports 15 (1): 15622. doi:10.1038/s41598-025-98233-3. ISSN 2045-2322. PMID 40320441. PMC 12050312. https://pmc.ncbi.nlm.nih.gov/articles/PMC12050312/.

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Analog television broadcasting topics

Systems|

* 180-line
* 405-line ( System A )
* 441-line
* 525-line ( System J , System M )
* 625-line ( System B , System C , System D , System G , System H , System I , System K , System L , System N )
* 819-line ( System E , System F )

Color systems|

* NTSC
* PAL
* PAL-M
* PAL-S
* PALplus
* SECAM

Video|

* Back porch and front porch
* Black level
* Blanking level
* Chrominance
* Chrominance subcarrier
* Colorburst
* Color killer
* Color TV
* Composite video
* Frame (video)
* Horizontal scan rate
* Horizontal blanking interval
* Luma
* Nominal analogue blanking
* Overscan
* Raster scan
* Safe area
* Television lines
* Vertical blanking interval
* White clipper

Sound|

* Multichannel television sound
* NICAM
* Sound-in-Syncs
* Zweikanalton

Modulation|

* Frequency modulation
* Quadrature amplitude modulation
* Vestigial sideband modulation (VSB)

Transmission|

* Amplifiers
* Antenna (radio)
* Broadcast transmitter/Transmitter station
* Cavity amplifier
* Differential gain
* Differential phase
* Diplexer
* Dipole antenna
* Dummy load
* Frequency mixer
* Intercarrier method
* Intermediate frequency
* Output power of an analog TV transmitter
* Pre-emphasis
* Residual carrier
* Split sound system
* Superheterodyne transmitter
* Television receive-only
* Direct-broadcast satellite television
* Television transmitter
* Terrestrial television
* Transposer
* Digital television transition

Frequencies & Bands|

* Frequency offset
* Microwave transmission
* Television channel frequencies
* UHF
* VHF

Propagation|

* Beam tilt
* Distortion
* Earth bulge
* Field strength in free space
* Knife-edge effect
* Noise (electronics)
* Null fill
* Path loss
* Radiation pattern
* Skew
* Television interference

Testing|

* Distortionmeter
* Field strength meter
* Vectorscope
* VIT signals
* Zero reference pulse

Artifacts|

* Dot crawl
* Ghosting
* Hanover bars
* Sparklies

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