Required Field and Receiver Sensitivity

Required Field and Receiver Sensitivity
SoftWright Home

Q: What is the difference between the values in TAP for “Required Field” and “Receiver Sensitivity"?

A: The Required Field value and the Receiver Sensitivity (sometimes called Receiver Threshold) are related values but they serve different purposes.

Note that all values in this example are for demonstration purposes only. You should determine appropriate settings for your application.

· Receiver Sensitivity is the manufacturer’s specified requirement for the input to the receiver necessary for minimum operation. This is usually specified as an input power (such as –110dBm) or voltage (such as 0.7uV) into the receiver impedance (usually 50 Ohms). This is the value that must be achieved at the receiver input terminals for a usable signal. This value is computed at the input terminals, after the associated gains (such as the antenna gain) and losses (transmission line, building losses, etc.). The value is based on a specific type or model of equipment.

· Received Signal Level (or RSL) is the calculation of how much power (or voltage) is actually available at the receiver input terminals. This value depends on the specific receiver configuration (antenna gain, internal losses) and the environment of the receiver equipment (body losses, building losses, etc.). Service to a particular location depends on whether or not the RSL equals or exceeds the manufacturer’s specified Receiver Sensitivity.

· Field Strength (sometimes called Field Intensity) is the level of field strength (usually in dB above one microvolt per meter, dBuV/m, and abbreviated “dBu”) at a location so that induces a voltage into the receiver antenna. That voltage, adjusted by the gain of the antenna and losses associated with the receiver (internal and environmental) is applied across the receiver input terminals and results in the power applied to the receiver.

· Required Field is the value computed by TAP (in dBu) necessary at any location to induce the necessary voltage in an antenna at that location and produce the RSL necessary for the receiver to function.

As described in the Required Field Value article, the benefit of computing coverage in values of field strength is that the field strength value in dBu at each location is independent of the receiver sensitivity, antenna gain, internal and environmental losses, etc. You can compute a coverage study one time, then apply the required field values applicable to different receiver hardware (sensitivity value, antenna gain, line losses) and environments (body losses, in buildings, outside of buildings, etc.) to see under what conditions the transmitted signal will provide adequate receiver operational.

In TAP you can plot the computed coverage either as field strength in dBu (showing the signal levels independent of receiver configuration) or as input power in dBm (showing the service for a particular receiver, antenna, and environment).

This discussion applies both to coverage (or “Talkout”) studies, considering the base station or Fixed Facility as the transmitter and the mobile unit as the receiver, and it applies to “Talkback” studies using the mobile unit as the transmitter and the Fixed Facility primary receiver configuration (antenna gain, line losses, receiver sensitivity, etc) for the receive unit. For Talkback studies you have the option to include losses (body, building, etc.) in the mobile transmitter section of the Mobile Facility record to include those losses in the Talkback study as well as the mobile receiver losses considered in the Talkout study.