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Choosing antenna tuner capacitor

Discussion in 'Radio Circuits, Repair & Performance' started by 9A5DLZ, Feb 16, 2016.

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  1. G4LNA

    G4LNA Ham Member QRZ Page

    Can I ask a question? Have you ever built anything? The reason I ask is in the spirit of amateur we like to build things ourselves if we are capable and it makes a great talking point on the air when someone finds out you've built something yourself and the person actually learns something in the process, instead of buying a black box, cheap or not.

    I can't speak for 9A3DLZ, but I'm not paid by the hour for my amateur radio activities, so the time is my own, so personally it doesn't matter how long it takes to build.
     
  2. 9A5DLZ

    9A5DLZ Ham Member QRZ Page

    REASTON thank you for your comment, but I agree with G4LNA. I like building my own stuff. There is nothing in the world that can replace that feeling you get when you finally make something that works. If this was something more complicated, like All-mode transceiver, I would admit, it's quite difficult to make it. But this is simple T-match and I will never believe if somebody says that professional T-match is better than my homebrew.
     
  3. PA1ZP

    PA1ZP Ham Member QRZ Page

    Hi

    Professionals do not use T-matches, as they often work with fixed frequencies they use dedicated fixed LC matching or a little variable match to tune their TX-es.

    And i build my own tuners as I had lots of tools available and could do a better job and cheaper then buying as I only had to pay for the used materials.
    I also could optimize the tuner for my specific needs for a tuner and leave out he stuff I didn't need.
    It also would be a unique tuner a one off.

    I also like building things myself, mostly for learning to understand things better.

    73 Jos
     
  4. G3YRO

    G3YRO Ham Member QRZ Page

    I agree, well worth building your own ATU! (I've never bought a commercial one in my life)

    The point is you can make it do what you want . . . mine has nice ceramic switches so I can select different antennas or dummy load . . . as well as different arrangements for the ATU.

    But certainly you don't want to be buying a brand new variable capacitor! Don't you have any Rallies over there where you can pick up surplus old capacitors etc nice and cheap? If not, then look on sites like ebay for ones removed from big old military transmitters.
     
  5. 9A5DLZ

    9A5DLZ Ham Member QRZ Page

    It's quite hard to find anything here in Croatia. If I buy a variable capacitor from ebay, I have to pay lots of money for shipping. I calculated around 70-80 dollars for two 400pF variable capacitors.
    We do have a hamfest somewhere in June, but I don't even know if there will be such things.

    Basically, before I got into this hobby I thought that radio amateurs here built their own equipment, soldered electronic circuits, experimented with them. But now it seems that nobody does anything. Or they just use echolink. On the other side, I absolutely hate echolink and 2m band.

    I decided to make 7 or 8 fixed capacitors from teflon and switch them in as needed. As G4LNA suggested.
     
  6. G4LNA

    G4LNA Ham Member QRZ Page

    9A3DLZ, If you are interested I can send you a copy of my spreadsheet to help calculate the size of the plates for the capacitor taking into account the Dielectric Constant of Teflon. If your email is correct on QRZ.com I'll send it to you.

    I little tip when you are building the capacitor, use Silicon grease between each layer, the reason is Teflon and PTFE is pretty slippery stuff and the Silicon grease holds each layer in place while you build each layer up, also the Silicon grease is an insulator. I will try and take some pictures of the construction sometime if that will help you.
     
  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    I agree....you can easily exceed 250 volts at very low power under the right conditions.
     
  8. KL7AJ

    KL7AJ Ham Member QRZ Page

    Yes....mineral oil will do the trick....just a bit difficult to implement in the ham shack~!
     
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    yes....a combination of switched fixed capacitors is a sound idea. The circuit might end up more complex than you like, though.
     
  10. KL7AJ

    KL7AJ Ham Member QRZ Page

    Please do!
     

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