What is harmful interference?
Interference is an unwanted effect caused by one radio signal on another service. It may block reception, distort a message or prevent a receiver from working correctly.
Prevent interference
The station must be designed, installed, maintained and operated so that it does not cause interference to authorised radio services. Correct frequency control, filtering, grounding and antenna installation help prevent problems.
Listen before transmitting
Before starting a transmission, listen to the frequency. Make sure that another station is not already using it. If transmission is likely to interfere with an ongoing contact, wait for a suitable break.
Action when interference occurs
Under the Indian Annexure, if the station causes interference, the operator must discontinue or restrict transmissions while adjustments are made when requested by the Central Government or a land station. Do not continue transmitting while a known interference problem remains unresolved.
Frequency accuracy
The transmitter must be tuned as accurately as possible. It must not radiate energy outside the authorised band limits. Frequency drift and incorrect VFO settings can cause out-of-band emissions.
Frequency measuring equipment
The 2024 Annexure requires reliable frequency-measuring equipment at the authorised station. The operator must verify the transmitter frequency each time it is changed and whenever needed to confirm that the emission remains within the authorised band.
Calibration and accuracy
Frequency-measuring equipment must be kept accurate. A frequency counter, calibrated receiver or suitable frequency meter can be used, provided it is appropriate for the measurement.
Damped waves
The Annexure prohibits emissions specified by the Government, including damped waves. Damped-wave transmission is an old form of poorly controlled, broad-spectrum emission. Modern amateur transmitters should use stable and properly controlled signals.
Prolonged calls
Avoid long calling sequences and unnecessary transmissions. Use concise calls and give other stations a chance to use the frequency.
RF interference to nearby equipment
Poor station layout can cause interference to televisions, audio systems, computers and other electronics. Check feeder connections, antenna matching, common-mode current and transmitter harmonics. Reduce power or stop transmitting while the cause is investigated.