Shoalhaven interference | ACMA


11 February, 2014 10:55 AM


Shoalhaven interference

By Editor

There is an updated blog about the Shoalhaven reception issue here.

Following a number of television reception complaints from viewers in parts of NSW south coast, particularly around Nowra and Shoalhaven, the ACMA visited Nowra in January and performed an investigation of the reported reception issues.

The available evidence from the ACMA’s field investigation in Nowra and signal monitoring of the television services from the Illawarra (Knights Hill) transmission site indicate that the reception difficulties could be caused by an anomalous form of radio wave propagation known as ‘seasonal ducting’. This phenomenon can cause distant television transmissions operating on the same channels, in this case Newcastle services, to propagate further than they normally would and cause interference to reception of services from Knights Hill.

Ducting is seasonal in nature and more prevalent during the warmer months. It occurs in many parts of Australia – predominately coastal regions, and is not unique to Nowra.

Seasonal ducting would also potentially affect the input feed of the Nowra North transmission site, which uses Knights Hill services as programming input, causing even more severe reception difficulties to all viewers watching the Nowra North services.   Local viewers and antenna installers have reported that services from the Nowra North site have also been affected. Broadcasters are considering options for improving the programming input to the Nowra North transmission site to provide more reliable coverage of the services from this site. 

Viewers watching Knights Hill services in marginal coverage areas or viewers with inadequate antenna installations are more likely to be affected. Viewers should consider visiting the mySwitch website ( to get location specific information about their digital television coverage, in particular whether they can get good coverage from the Ulladulla (Little Forest Trig) transmission site, as this site should not be affected by ducting.

In general, an experienced antenna installer should be able to recommend the best antenna type, placement and orientation for adequate reception. The antenna installer should also be able to identify any localised interference that may be affecting television reception. In that case, the installer can assist the viewer to lodge a request for interference investigation with the ACMA. More information can be found here.

Viewers receiving services from Illawarra (Knights Hill) and Nowra North, should also be aware of a number of planned outages at these transmission sites which are scheduled in February. These outages are related to the necessary infrastructure changes at the sites in preparation for the upcoming retune in May (Nowra North) and  June (Knights Hill). 

Viewers can find all the information about the retune and associated outages on and . For any further questions, viewers are encouraged to contact the Digital Ready Information line on 1800 201 013 or relevant broadcasters for assistance.