What does the term “contour” mean in broadcasting, and what distinguishes a “50,50” contour from a “50,10” contour?

A contour in broadcasting refers to the geographical area where a radio or TV station’s signal can be received at a specific signal strength level. Contours are used to predict the coverage area of a broadcast station as well as areas where the station could potentially cause interference to other stations.

The terms “50,50” and “50,10” refer to specific contour measurements used in the broadcasting industry:

1. 50,50 Contour (F(50, 50)): This represents the coverage area where a station’s signal can be received with a field strength that meets or exceeds a specified level in 50% of the locations, 50% of the time. In simpler terms, it’s the primary service area of a station where the signal is expected to be strong and reliable.
2. 50,10 Contour (F(50, 10)): This contour is used to determine interference potential. It represents the area where a station’s signal can be received with a field strength that meets or exceeds a specified level in 50% of the locations but only 10% of the time. This contour helps assess the potential for interference between stations, especially in areas where signals from multiple stations may overlap.

These contours are calculated based on various factors, including the station’s power, antenna height, and terrain. They are crucial for frequency allocation, station placement, and interference protection in the broadcasting industry.

Contours in broadcasting refer to a standardized method for predicting a station’s coverage area and identifying areas where it might cause interference to other stations. These predictions are based on whether a signal can be received at a specified field strength by 50% of the receivers, 50% of the time. This concept is known as the F(50, 50) curve and is primarily used for determining the coverage of FM radio and analog television stations. Another similar concept is the F(50, 10) curve, which considers reception by 50% of receivers but only 10% of the time, and it’s used to assess interference. For digital television, there’s the F(50, 90) curve, which accounts for more stringent signal strength requirements.

These curves are represented on charts. In the past, engineers had to determine the curve’s value at specific X and Y coordinates on the chart. These coordinates were based on factors such as the station’s height above average terrain and the field strength at 1 kW effective radiated power (ERP). The curves take into account the distance from the transmitter location to predict coverage.

The F(50, 50) chart is an example of this concept and is used to estimate the coverage area for broadcasting.

Contours in broadcasting are essential tools used to predict the coverage area of a broadcast station and to identify potential areas of interference to other stations. These calculations are based on specific field strength criteria that indicate whether a signal can be received at a certain level by 50% of the receivers, 50% of the time. Two common contour calculations are the F(50, 50) and F(50, 10) curves, each serving a different purpose.

1. F(50, 50) Curve: This curve is used to determine the general coverage area of a broadcast station. It signifies that the signal should reach 50% of the receivers within its service area, 50% of the time. It’s typically used for assessing the coverage of FM radio and analog television stations.
2. F(50, 10) Curve: This curve is used to evaluate interference potential. It requires that the signal reach 50% of the receivers within its service area but only 10% of the time. It helps assess the likelihood of interference between stations.

The calculations for these contours are typically plotted on charts. Historically, engineers had to manually determine values at specific coordinates on these charts, which were based on factors like antenna height above average terrain and field strength at 1 kW ERP. These curves consider the distance from the transmitter location and provide insights into the station’s coverage and interference potential.

For regulatory purposes in the United States, the FCC has specific rules regarding contour overlap, especially in scenarios involving different station classes and frequencies:

• For reserved band (88.1~91.9) FM stations and commercial band FM stations seeking short-spacing, there are rules to prevent overlap between interfering and protected contours.
• FM translators have specific rules governing contour overlap, allowing the proposed station’s service contour to be within the interfering contour of the incumbent station.
• Full-service FM stations have distance separation minimums based on maximum facilities and terrain conditions to ensure protection in both directions.
• LPFM stations use distance separation minimums to prevent interference with incumbent stations, with an additional 20-kilometer buffer zone for full-service stations.

These contours are crucial for allocation purposes and may not always represent the actual coverage experienced by listeners. Antennas located under 30 meters HAAT are considered 30 meters HAAT for allocation purposes, which can affect stations’ actual signal reach. It’s important to keep in mind that contours serve as a regulatory and planning tool and may not always reflect real-world conditions accurately.