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Homebrew Help Request

Discussion in 'Home Brew' started by KG6EAK, Jul 28, 2010.

  1. KG6EAK

    KG6EAK Member

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    I'm going to be building a homebrew satellite antenna over the weekend.

    I am confident that I will have little trouble doing so, in the construction of the actual antenna. I've built some different antennas in the past.

    Here's my problem though.

    In building the duplexer/diplexer, the parts list I have, is requesting certain ceramic capacitors. 4.7 picofarad, and 10 picofarad. Seeing nothing like that at my local shack shop, I came home, and used a capacitor conversion chart, to see which microfarad capacitors I could use in their place. Same local shack shop carries NOTHING with that many zeros in it (they do carry the 10 picofarad cap. Not ceramic. Electrolytic.)

    Does anyone have any suggestions? Cap substitutes? Can I use a bigger cap? smaller cap? (Do the caps have to be 4.7 microfarad, & 10 microfarad?) I live in a town of maybe 10,000 people. The closest anything besides this shack is over 2 hours away in Las Vegas.



    Ham radio is pretty dead out here, so I figured if I can work the birds, it will keep my interest peaked, and my radios will not end up dusty, in a box.

    Any suggestions will help the gears of progress to turn faster.
    Thank you.

    ~Brian
     

  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    A diplexer/duplexer is a highly tuned piece of gear and it needs to be built with the proper value components. You can't just substitute values or types of components.

    No offence but I can see by some of your comments that you don't really understand electronics that well. This part especially "(they do carry the 10 picofarad cap. Not ceramic. Electrolytic.)" There is NO SUCH THING as a 10 pF electrolytic capacitor, a 10 microfarad electrolytic yes, 10 picofarad no. Also you need to use either ceramic capacitors, or even better, mica capacitors and they are only found in small values, usually orders of magnitude smaller than one microfarad. One microfarad and up values tend to be used in audio circuits or power supplies and never in RF applications especially in VHF/UHF applications.

    Try the internet for what you want. Mouser is a good start. They may have a minimum order but it's always easy to blow a few extra bucks on connectors that you will need anyway.
     
  3. KG6EAK

    KG6EAK Member

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    Cap. Kilowatt,

    Thanks for your reply. Here's what I meant

    10 picofarad = 0.00001 microfarad. I meant they carry that particular cap, in an electrolytic form. (0.00001uF).

    Thanks for the advice, I will seek out exactly what the duplexer calls for.
     
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    OK, I thought you meant 4.7 microfarad or 10 microfarad rather than 0.00001 microfarad. That's just another way of writing the numbers. Remember that picofarad is a micro-micro farad so there are 6 decimal places difference. A 10 pF cap is in fact the same as a 0.00001 microfarad.
     

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