Electronic – What does the term “fixed” mean on the radio spectrum

A decibel is a unitless ratio and needs a reference point. Never use it without one. Especially you audio engineers! dBSPL!

Depending on the application, a signal strength may be measured in dBW or dBm. Both being units of power with a difference of 1000, conversion between dBw and dBm can be obtained by adding or subtracting 10log(1000) or 30.

There are many different definitions of bandwidth and engineers are used to switching back and forth between them and comparing apples and oranges to get the correct answer that they both are fruit. For example, if one says that the bandwidth of a lowpass filter is 10 kHz, then usually it means that the output power of a signal at 10 kHz is attenuated by a factor of 2 (3 dB attenuation) compared to the output power at DC. It is not the case that signals above 10 kHz are blocked entirely; if that were the intent, then the filter would have been referred to as an ideal lowpass filter with a cutoff at 10 kHz. For commonly used low-pass filters, the output power decreases at the rate of n dB per octave as the frequency increases beyond the 3 dB point, where n depends on the filter order: sharper decreases require higher-order (and thus more expensive) filters.

Similarly, if your antenna is usable from 2400 MHz to 2588 MHz, then I would hesitate at using it for signaling at a carrier frequency of 2588 MHz since the upper sideband would be attenuated considerably compared to the lower sideband. You want to be sure that the entire signal bandwidth fits comfortably within the specified range of operation.