Dear friends, for the first question, I do not really understand what does it means by "to provide a loss of no more than 0.5dB" ? For the second question, how do I find the upper cutoff frequency of high pass filter ? The answer I get it seems to be the lower cutoff frequency >< Thanks !
For a low pass filter, the loss is the attenuation at DC. For the second question, it looks like whoever wrote the question originally had it written for a bandpass filter and then copied the question and changed it to a highpass filter without realizing that the question wording didn't apply to a highpass filter. What is the "midband" of something that extends to infinity? About the best you can do is interpret the question to be asking for the attenuation in the passband (i.e., for "infinite" frequency) and for the lower cutoff frequency.
So the 0.5 dB consider as voltage gain ? I don't understand why we should do like that . can anyone further explain ? Thanks !
dB is a measure of power ratios. The logarithm is used for several reasons. First, if you have multiple stages then the overall gain is the product of the individual gains, but if you use logs then it is the sum of the logs. Humans are much, much better at adding things than we are at multiplying things. Second, the gains of many stages, and especially collections of stages, can be many orders of magnitude. This is particularly true when dealing with the attentuation of RF communication channels.
The 0.5dB is the loss (notice that it said "a loss" of no more than 0.5dB). So that means a voltage gain of at least -0.5dB.