Having gone through meta for such question, and finding one regarding circuit design review, I completely understand that view that "circuit designs" dumped on community for crowd-sourcing review comments is bad and frowned upon.

However, was wondering if there is some acceptable way, which amounts to asking for help design circuit, that is definitely beyond one's league in terms of understanding / appreciating in detail ?

For example, I am (a noob, especially when it comes to UHF RF electronics) trying to create a solution that tries to locate 434MHz RF beacon signal, in an area the size of a small farm. Now I have "found" an almost ready-to-use circuit schematic that can convert RF signal strength dB value (scaled DC output). However it has a relatively wide operating frequency range, which covers GSM (900MHz, 1800MHz), 3G (2100MHz) and WLAN (2400MHz) as well, where there is significant chatter, which is why I need a band-pass filter to help me detect signal strength in 434MHz range. Having searched with terms like "434MHz band pass filter", I have come across this calculator. For the input values, I am using value of RL=53 Ohm, Freq=434 MHz, but not sure what to use for loaded-Q ? From this wikipedia article on band-pass filters, I think the loaded-Q might be the Q-factor(!), and what I believe I need is a narrow-band filter, so with high-Q. However, I am having difficulty calculating loaded-Q. Found this definition:

Loaded Q (Working Q): A term that defines the percentage of the 3db bandwidth of a Bandpass Filter. Q=Center Frequency (Fc) in Hertz/ 3dB Bandwidth in Hertz

Now, I believe that Fc in my case is 433.92x10^6 Hz (right?), but not clear on what "3dB Bandwidth in Hertz" means.

However, I've read other posts which talk about the difficulties of working with any circuit at such high frequencies (s.a. in the UHF range), due to parasitic effects, and if I understood it correctly, then the extensive use of ground-plane, i.e. definitely must work with at least 2-sided PCB, and nothing that can be done on a breadboard.

While I cannot claim to have done everything possible to answer the question myself, but I trust that I've put some reasonable effort in going as far as my current level of knowledge would allow. I understand that one expected answer is, this is clearly beyond your league, and you shouldn't even attempt such a thing. Fair enough, but could I insist ? Maybe in a different forum, or say over chat ?

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    \$\begingroup\$ Chat is always a place to come talk about things, we very often have the back and forth discussion that makes certain questions very easy to answer. Sometimes people will say that a task seems out of your league, but if you focus down the task to subtasks then it should become very rare. An answer of, "You are too deep to figure this out." is not an answer imho. \$\endgroup\$
    – Kortuk
    Dec 19 '12 at 16:38
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    \$\begingroup\$ Thanks @Kortuk. That is quite reassuring, will give chat a shot. \$\endgroup\$
    – bdutta74
    Dec 20 '12 at 12:42

It really sounds like many sub questions you need to ask, one for each issue you are running into, some need to be asked first, and after answered, move on to the next. You are correct, a big "How do I do this problem question" is not a great fit as it will be mostly anyone weighing in with sub opinions on the parts they know, but each sub question I see here asked separately seems like a well focused question.


This is an interesting case, as the examples of the specific questions might actually lead to rabbit holing the wrong answer. Eg. if you're trying to find a beacon at that frequency in that sort of area you'd probably do better with a doppler direction finder. I think only the over arching question about methods would elicit that response, rather than getting stuck in a series of questions about designing a signal strength meter.


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