Why is 707 the half power frequency

Search Advanced search…. New posts. Search forums. Log in. Install the app. Contact us. Close Menu. Welcome to EDAboard. To participate you need to register. Registration is free. Click here to register now. Register Log in. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.

You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser. Please explain the term 3dB Bandwidth. Thread starter Hamidzia Start date Jul 25, Status Not open for further replies. Hamidzia Member level 3. Please explain the term '3dB Bandwidth'. That is the gain has a certain variation with the frequency of the signal. Best regards gam. Kevin Weddle Advanced Member level 4.

Re: 3 dB Bandwidth I like the graph. It answers the question nicely. This describes the unit circle which has a radius equal to one. The adjacent is equal to one, the opposite is equal to one, the hypotenuse is equal sqrt2. Thank you very much to all Specially to gam for a very comprehensive detail and graph. Now i have a good idea of the term. Tell me that can we call 3dB bandwidth as half power bandwidth?

Is 3dB Bandwidth is nothing to do with the numeric value '3dB'? Is the numeric value just used for no reason? Thanks again. Re: 3 dB Bandwidth The half power comes from the fact that sin45 times V quantity squared is equal to. I think the magic number deals with the fact that at 45 degrees, the radius and the heighth are equal to one, which is dimension of the unit circle. Note that this is a ratio of two things with the same unit watt. A ratio such as this does NOT have a unit it is dimensionless.

The "unit" dB is only used to stress the fact that you are giving the ratio of powers in log domain and not in "linear" domain. Then because you you use. The advantage of thinking about it this way is that you can determine fc from low frequency simulation and do not have to have any a priori knowledge of fc to know what range of frequencies to simulate over to properly bracket it.

You cannot easily measure at this low frequency, and if there is any nonlinearity then a 1V signal will introduce distortion, but in a simulator an ac analysis is done on the circuit linearized at its dc operating point and you can easily simulate at any frequency, so it works like a charm.

I think, all of the given justifications are appropriate - however, we should not forget that this -3dB limit is an arbitrary one. There may be good reasons for choosing this value - on the other hand, some filter approximations with passband ripple Chebyshev, elliptical do NOT use this 3dB limit. In some particular cases it can be necessary - even for Butterworth filters - to specify the band edge at the 1dB or 2dB frequency.

Thus, the 3dB limit is not a "natural" threshold - it just makes sense for many applications. The 3dB point corresponds to half Power Point ie. No answer is voted up by Cyril Robinson, the man who asked this question. Till now there is no response from him on all the above answers. IS he still not satisfied with these answers. Excuse me,t he most important vote is that of the asking person! From my point of view the voting system is not a sufficient measure for answers evaluation.

Some better answers collected less votes! Thank you Prof. Lutz for providing info on the relevance of 3 dB cutoff points regarding some other filters like Chebishev, Butterworth Filters etc. An international definition for bandwidth, while u can defined yours say 6dB or 10dB.

Depends on the manufacturer. Else what so ever other members say is correct. Thank you.. Sorry for replying late sir. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous. Carousel Next. What is Scribd? Uploaded by Igor Gjorgjiev. Did you find this document useful? Is this content inappropriate? Report this Document.

Flag for inappropriate content. Download now. For Later. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Join for free Please tell me, Why the cutoff frequency is taken for 3dB and not other values like 1 or 2 db? Krieger University of Alberta Generally speaking, a filter's cutoff frequency is not necessarily defined at -3dB. Feb 9, Suresh Susurla Indian Institute of Technology Madras As answered by other friends, actually the frequency corresponding to 3dB magnitude is considered as bandwidth of the signal or of the system.

Feb 9, Samir Ben Abid -3dB means that only half of the signal's power is attenuated by the filter. Mar 9, Stephen Hall University of Liverpool This seems a very inefficient way of finding out very basic knowledge. Why not simply look in a textbook? Mar 14, Shailesh Kumar Dr. Patil University 3dB corresponds to the half of the maximum power. Apr 2, Jagadish Kadadevarmath Karnatak University, Dharwad Particularly in communication applications it required to have constatnt gain over lager bandwidth.

Apr 3, Kurt Lathrop It's not really arbitrary. Apr 7, A. It is simply a convention. You can be sure it's referring to the preamplifier. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. What is the significance of -3dB? Ask Question. Asked 10 years, 11 months ago.

Active 4 years, 9 months ago. Viewed k times. Thomas O Thomas O Add a comment. Active Oldest Votes. So originally we had 36 W, now we have 18 W which of course is half of 36 W. Application of -3dB in Filters The -3dB point is very commonly used with filters of all types low pass, band pass, high pass Why filter the input to an Oscope? Community Bot 1. Kellenjb Kellenjb When they rate the scope they are just saying that you will be able to get accurate readings within 3db up to that frequency.

An AC signal of a given amplitude will change at a rate proportional to the frequency, and many circuits have parts which will not behave properly on signals which change too fast. If one didn't include such an filter, the maximum distortion-free input level Show 6 more comments.

The expression holds, obviously, but what suggests the use of the sine in the first place for the phase Bode plot? Ditto non-linearity, for the most part. Ditto preamplifiers. The 3db attenuation point does not refer to the preamplifier's limitation only, but the input system as a whole - which is not designed to exceed MHz. Sign up or log in Sign up using Google.