ANSI SCTE-144-2007 pdf download Test Procedure for Measuring Transmission and Reflection
2.2.5 Bandwidth: The frequency range that brackets the linear operation of a device. The endpoints of narrow band devices like filters are usually characterized by the frequencies where the transmission response has dropped by 3dB. The bandwidth of wide band devices like splitters, directional couplers and amplifiers is usually defined by a frequency response or flatness specification that applies to the boundary frequencies of the application.
2.2.6 Frequency response: The way that a device modifies the signal flow at each given frequency. This is often synonymous with flatness with respect to the transmission response.
2.2.7 Slope: A measure of the monotonic frequency response of the network from low to high frequency. Slope is positive, or upward going, if the gain increases as the response is swept from low frequency to high frequency. Slope can be derived numerically from the forward transmission data set. A linear trend line is constructed through the transmission data. It has the general form y=mx+b. Since it is linear, it is most representative of the overall slope response when it is derived from the linear portion of the response, not the endpoint frequencies. A spreadsheet can apply the SLOPE function to the transmission response data. This yields ‘m’ in the equation for the trend line. Then the spreadsheet can apply the INTERCEPT function, which calculates the value ‘b’ where the trend line crosses the y-axis. From these two constants, the trend line is constructed as a set of data points of transmission vs. frequency. Multiplying the full frequency range by the factor m yields the value for the slope.
2.2.8 Flatness: The maximum peak to valley excursion of the transmission response over the specified bandwidth. The flatness can be derived numerically from the forward transmission data. Flatness is expressed as a + tolerance around a line through the mean linear response. Once the trend line is established as a data set (see slope definition), the actual transmission data can be compared to it. The difference between the trend line and the response is computed for each frequency, and the spreadsheet applies the Min and Max function to this data set. This establishes the peak to peak deviation, which is then divided by 2 to yield a +/- value for the frequency response.
2.2.9 DUT: Device Under Test