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RF generator and capacitor question

Discussion in 'Home Brew' started by TruckerKevin, Mar 4, 2018.

  1. TruckerKevin

    TruckerKevin New Member

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    The manual of my RF signal generator says that I should use a 1-5 pf capacitor in line when checking RF an IF amplified circuits to prevent detuning effects. So this is applicable when I am injecting a signal into my radio to set the receive on a VU meter?

    I have looked at charts but get even more confused when trying to work out the values of said capacitor.. I have a pack of ceramic capacitors labeled 0.1 mfd

    I have another box of electrolytic capacitors that range from 0.1 uf and go up to 470uf.



    Will any of this work? Or are al of these way out of range?

    And if they do, and I can use one of the electrolytic types, those have a negative and positive side, which way should it be oriented? The negative side towards the generator?
     

  2. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    NO on the electrolytic caps. It does need to be a ceramic disc. I would buy the capacitor in the value recommended. The main reason of using the caps is to isolate the signal generator from any DC voltages present. Either in the unit under test or coming out of the signal generator.
     
  3. TruckerKevin

    TruckerKevin New Member

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    Is the 0.1 us the same value as the 1 pf or is it way off
     
  4. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    0.1uf = 100pf
     
    Tallman likes this.
  5. TruckerKevin

    TruckerKevin New Member

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    So a 1 pf is a 0.01?
     
  6. Robb

    Robb Yup

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    It's confusing; but not quite.

    .1uf (microfarads) is equal to 100nf (nanofarads) and is equal to 100,000pf (picofarads).
    lol - I hope I got it right - too!
     
  7. TruckerKevin

    TruckerKevin New Member

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    I just ended up ordering a pack of 3 pf off eBay to make sure I’m getting what I need lol
     
    Shadetree Mechanic likes this.
  8. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    You are right, I should have looked it up before I posted.
    Here is a chart from Wikipedia:




    Metric prefixes in everyday use


    Text

    Symbol

    Factor

    Power

    exa E 1000000000000000000 1018
    peta P 1000000000000000 1015
    tera T 1000000000000 1012
    giga G 1000000000 109
    mega M 1000000 106
    kilo k 1000 103
    hecto h 100 102
    deca da 10 101
    (none) (none) 1 100
    deci d 0.1 10−1
    centi c 0.01 10−2
    milli m 0.001 10−3
    micro μ 0.000001 10−6
    nano n 0.000000001 10−9
    pico p 0.000000000001 10−12
    femto f 0.000000000000001 10−15
    atto a 0.000000000000000001 10−18
     
    #8 Shadetree Mechanic, Mar 4, 2018
    Last edited: Mar 4, 2018
  9. Robb

    Robb Yup

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    .01 of what? You have to use a suffix to assign its relative order of magnitude. If you are saying .01uf; then that would be equivalent to 10nf, or 10,000pf . If a disc cap says .1uf; then it is one tenth of a microfarad. If a disc cap says .01uf; then it says it is one hundredth of a microfarad. If it said .001; then it would be one thousandth of a microfarad.

    Dunno if it made that point any clearer for you. For the most part most electronics use just three magnitudes/values: pf, nf, and uf. pf being the smallest. 1nf is equivalent to 1000pf, and 1uf is equivalent to 1 million pf. Degrees of holding so much/little charge.

    Lets say that one pf is a single dollar. If you have a thousand dollars, it would be the same a 1nf. If you had a million dollars, you would have 1uf. How many pf would .01uf equal? 10,000 dollars. Better/that help?

    What if you had .01uf? How many dollars would that be? Well one hundredth of a million dollars would be ten thousand dollars - or 10nf. It will take a little getting used to; but you'll get it.

    Some caps value might say '473' or perhaps '103', '333', '562' - using numbers like that. This is a different system to display a cap value - is all. What that means is that it is - in the case of 473 - 47 plus three zeros added to its end. Soooo, 473 would equal .047uf or 47nf or 47,000pf. And so on.
     
    #9 Robb, Mar 4, 2018
    Last edited: Mar 4, 2018

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