Specify a Limit Using a Formula
- Updated2024-06-07
- 1 minute(s) read
Specify a Limit Using a Formula
You can specify limits using formulas. Such limits are best classified as segmented limits.
Each segment is defined by start and end frequencies and a formula. For example, the ANSI T1.413 recommendation specifies the limits for the transmit and receive spectrum of an ADSL signal in terms of formula. The following table, which includes only a part of the specification, shows the start and end frequencies and the upper limits of the spectrum for each segment.
| Start (kHz) | End (kHz) | Maximum (Upper Limit) Value (dBm/Hz) |
|---|---|---|
| 0.3 | 4.0 | -97.5 |
| 4.0 | 25.9 | -92.5 + 21.5 log2(f/4,000) |
| 25.9 | 138.0 | -34.5 |
| 138.0 | 307.0 | -34.5 - 48.0 log2(f/138,000) |
| 307.0 | 1,221.0 | -90 |
The limit is specified as an array of a set of x and y points, [{0.3, 4.0}{-97.5, -97.5}, {4.0, 25.9}{-92.5 + 21.5 log2( f/4,000), -92.5 + 21.5 log2( f/4,000)}, …, {307.0, 1,221.0}{-90, -90}]. Each element of the array corresponds to a segment.
The following figure shows the segmented limit plot specified using the formulas shown in the previous table. The x-axis is on a logarithmic scale.
