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Simple alternatives protoboards for RF circuit design

  1. May 28, 2012 #1
    I've found out very quickly that I can't use a breadboard for RF circuits, what is another choice? I know PCB's would be best but making them is very tedious for me. I'm new at this stuff so I plan on experimenting quite a bit which is another reason I want something quick and easy to replace components. The frequencies are gonna be between 100MHz and up to 400MHz..

    Thanks for any suggestions
     
  2. jcsd
  3. May 28, 2012 #2
    It is very hard to breadboard rf circuits. 100 to 400MHz is not the highest, you can still carefully solder the surface mount components together. But still the result might be different when you put onto the pcb. Layout is everything. The wave length of the frequency become an issure pretty fast.

    Now a days, you can get a 4 layer pcb quite cheap, you might want to do that. Also, you should avoid leaded components, you have to use surface mount components.
     
  4. May 28, 2012 #3

    vk6kro

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    You might like to try "dead bug construction".
    Like this:
    http://www.qrp.pops.net/ugly.asp

    This actually works better than printed circuit boards at VHF and is ideal for quick prototypes.
    Once you have a project going, you can think about either putting it in a nice box so that the appearance doesn't matter, or you can make up a PCB knowing the circuit has been optimized.

    Unless you already know a circuit works, putting it straight onto a PCB without prototyping is a recipe for disaster. At VHF, proper grounding and bypassing are essential and this is achieved better if a ground plane is immediately under your circuit.

    It is important to anchor any wires that have to leave the circuit carefully. One way of doing this is to buy strips of header pins,. normally used in computers. These can be broken into short lengths of 5 or 6 pins and tag strips made by clipping off unwanted pin ends.
    http://www.altronics.com.au/images/prod/P/P5430.gif
     
  5. May 28, 2012 #4
    Short of doing a run of pcb, dead bug is the only way. I did a lot of dead bug bread boarding up to 200MHz with leaded components. Infect, that's what I did all these years. 400MHz is pushing it. The reason is when you dead bug, the connections are all up in the air, it start to behave differently.

    Dead bug with SMD components is not easy. You'll find changing components not easy by any stretch. As they are leadless, they don't flex, it is hard to change components and easy to break the components.

    I find doing a 2 layers pcb very efficient, even if you make a lot of mistake, it is easier to fix. Yes, layout is everything, I did all my own layout for RF circuits.
     
  6. May 29, 2012 #5
    Thanks for the replies.

    That dead bug thing really does look ugly :smile: but I might try it if I can't find anything else.

    I was looking around for some breadboard-type solutions and came across these:

    http://www.futurlec.com/ProtoBoards.shtml

    Prototyping boards, experimenter's board, and stripboard. I've never seen these before but would they work?
     
  7. May 29, 2012 #6

    vk6kro

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    If you are building a circuit out of a book or a magazine, then they should work if you wire them up properly.

    So, you can use those boards for low frequency work.

    However, for VHF or if you might need to optimize the design, dead bug is a lot better. Don't worry about what it looks like.
     
  8. May 29, 2012 #7
    None of them is good. I was trying to find the one I used before. It has a ground plane on one side. It has 0.1 pitch plated holes.

    What you show has no ground plane, also different trace pattern create unwanted trace length hanging on the signal path.

    For the kind of frequency, you have to have a ground plane, no unnecessary length on any connection. Dead bug is ugly but that's your best bet if you are not willing to do a pcb run. If you complain about dead bug looks ugly, you don't do RF circuits!!! Thats pretty much the standard short of a pcb. Even if I can find the perforated ground plane board, it is not going to be as good as the dead bug. You are in the RF world!!!!

    Don't discount the possibility of doing pcb. If you can do it in 2 or 4 layer, it'll give you a good idea how the circuit behave when put onto the board. You can do dead bug and get certain result, that has no guaranty you get the same result when put onto the pcb. So you might end up have to make a second run anyway. 2 and 4 layer boards are very easy to modify even if you make mistake, so it's not a waste of time and money.

    You are only doing 400MHz, that is low enough frequency that dead bug might work. From my experiment, I never seen people breadboard anything higher frequency than that. Instead we use a proto board milling machine that take a two sided ground plane FR4 board and mill out the trace patent. There is nothing easy about RF. Wait until you start probing and testing the circuit, I can assure you if you don't see the waveform you want, 80% of the time is your measurement setup, how you ground your probe leads and all. RF is a different world.
     
    Last edited: May 29, 2012
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