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does it matter what 10pf capacitor i use as long as its rated for more voltage than required

Discussion in 'General Electronics Chat' started by jambo6984, Nov 13, 2017.

  1. jambo6984

    jambo6984 New Member

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    I was trying to find a blue 10pf capacitor i think it was a multilayer cap but all i can find is yellow ones rated for 30v multilayer im trying to use it in a fm transmitter and i have regular ceramic 10pf capacitors my question is does it hace to be a multlayer like the one in the picture im trying to replicate and if it does, does it matter if i go with a bigger voltage rating and if not that would be great because i have regular ceranic 10pf caps please someone shine some light on this im oind of new to electronics and need to know if i already have what is needed or if i need to find the exact blue multilayer kind or if i need to go ahead and order the yellow multlayer 10pf caps any help would be greatly appreciated thanks in advance
     
  2. dknguyen

    dknguyen Well-Known Member

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    The voltage rating matter won't as long as it's sufficiently high. Whether it's multi-layer won't matter either. What will matter is the material type of capacitor, especially in something like a radio.

    Something as small as 10pF in a radio, is probably in the signal path so it's going to have to be accurate, stable with temperature and applied voltage, with good frequency characteristics. Use something at least as good as a C0G/NP0 ceramic for something like this. If the caps you already have are C0G ceramic then you probably can use them. I don't know of any ceramic caps more stable than C0G. The next step up are things like film caps or mica caps which would also likely work.

    The other types of ceramics aren't good enough for something like this. They have names that look like X7R, X5R, Y5V They aren't stable enough for signal-path stuff and are only sufficient for power decoupling.

    I should note that 10pF is so small that it probably is a C0G/NP0 cap unless you explicitly know that they are not. That capacitance is so small that it's pretty much useless for any application that might need it unless it's C0G.
     
    Last edited: Nov 13, 2017
  3. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Your poll doesn't include "color" as a choice. Be sure you get blue ones.:woot:

    Sorry, I agree with dknguyen, except to mention there are some other choices, like mica, polystyrene and polypropylene. Unfortunately, you have not described what it does int he circuit. Is it critical to the frequency? Used as part of a filter? Of course, the ceramic are more available and cheaper.
     
  4. dave

    Dave New Member

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  5. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    The power supply doesnt necessarily state the working voltages in the circuit and this particularly applies to a transmitter, however it sounds like this is a low power fm bug type thing, so 30v will probably be fine.
    As well as the types mentioned you could also use a silver mica (expensive).
    Everything so far assumes that the capacitor is in a frequency dependant part of the circuit like the LC tank, if its just decoupling or a filter then it doesnt matter so much, post or link a schematic we'll tell you.
     
  6. jambo6984

    jambo6984 New Member

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    is the youtube video of were the project is and he did use blue which confused me because i looked it up and it was a really high voltage rating sorry im a little new to electronics im a expert in any kind of wiring that doesn't include circuits and im trying to get good at it and have ordered about everything i would ever need off of banggood.com its a really cheap site and you get your stuff 7 to 20 days sorry for any misspelled words typing fast and i really appreciate any help and all help already given
     
  7. jambo6984

    jambo6984 New Member

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    I think the blue capacitor im seeing in the video is a multilayer cap tge way it looks but if someone watches the video and knows for sure what it is please let me know especially if theres no way around using that specific kind thanks in advance for any and all advice
     
  8. dknguyen

    dknguyen Well-Known Member

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    Don't get hung up on whether it's multi-layer or not. That part doesn't matter. It's just a type of construction to put more capacitance in a smaller physical size.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    That FM transmitter is so simple that it will sound awful on an FM radio. It is missing the "pre-emphasis" (look it up in Google) that all FM radio stations have. Pre-emphasis boosts high audio frequencies then all FM radios have matching de-emphasis that cuts the boost down to normal and cuts hiss. Without pre-emphasis, the sounds heard on an FM radio will be very muffled with high frequencies reduced like your stereo with its treble tone control turned all the way down.

    The simple FM transmitter will also change its radio frequency when something moves towards or away from its antenna and as the battery voltage runs down.

    The video does not have a schematic or a detailed parts list. What is the recommended transistor part number? American, European and Oriental transistors all have different pin functions so look on the datasheet of whichever transistor you are using.
     
  10. jambo6984

    jambo6984 New Member

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    Thanks everyone for all the excellent advice this is just a project to get some kind of circuit to work btw my first fm transmitter didnt work i have put together a electronitc kit transmitter that works but still havent made my own circuit yet, that works it wont be used other than verifying that it works then i will try to go slowly to more complicated stuff again thank you for all the great advice
     

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