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# DAB+ layer 6 – How does Broadcast Partners calculate field strength & care

Background
Not everyone is familiar with the calculation of the maximum possibilities of a DAB allotment in Layer 6 and the range you obtain from it. Below is a brief explanation of how field strength calculations should be performed and presented for a correct picture.

There are two types of field strength calculations that are also factually different:

• theoretical field strength calculations, necessary to verify compliance with Article 4(2) of the license conditions;
• practical field strength calculations that represent the receiving area (care) based on actual transmitter data.

Theoretical Field Strength Calculations

Article 4 paragraph 2 of the permit states, that the permit holder shall not cause a field strength level higher than 50 dBÎ¼V/m at 10 km distance from the allotment and not more than 40 dBÎ¼V/m at 30 km distance from the allotment. So you’re not allowed to cross that. You calculate this using the propagation model from ITU Recommendation 1546. The details of the calculation method are in chapter 4,2nd paragraph of the explanation of the broadcast license.

The transmitter provides radiated power per antenna direction. For a transmitter network (2 transmitters or more), the individually calculated field strength values per transmitter at each point of the contour are summed using the so-called power-summing method. It is the single calculated field strength or the summed value that must meet the maximum stated field strength values of the permit. The calculations to be made in this way serve only to protect other allotments and say nothing about the expected care. You obtain what is known as a theoretical maximum diagram with this.

Practical Field Strength Calculations

These practical calculations serve to represent the transmission range. The permit conditions say nothing about that. The practical interpretation of the theoretical maximum diagram is the starting point for this. Furthermore, Broadcast Partners uses the following assumptions for the practical calculations:

• height of receiving antenna 1.5 meters above the ground;
• care is a minimum field strength for a receiver to operate without interference;
• in open areas, a lower field strength is sufficient than in urban areas;
• for indoor reception, higher field strengths must be taken into account, due to building attenuation and all kinds of electrical interference (man-made-noise);
• the spread in the quality of the receivers is wide. An average quality receiver is therefore assumed;
• the topography of the site is a co-determinant of the calculated field strength.

To meet these principles, Broadcast Partners uses the Longley-Rice propagation model. This model is ideally suited to do field strength calculations at 1.5 meter reception height. When presenting care, Broadcast Partners uses a color scale that represents the probability of good reception. It progresses in a gradual scale from yellow to red. At yellow there is a chance of mobile reception in open terrain, up to red for a chance of indoor reception. Not all pictures in the market are created this way; however, you can be sure that Broadcast Partners’ calculations and presentations meet these requirements.