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Best Antenna and Rectifier Diode

  1. Jul 10, 2013 #1
    What must I do to maximize the voltage received from an antenna?
    Also, what kind of rectifier diode has the lowest voltage cut?
     
  2. jcsd
  3. Jul 10, 2013 #2
    welcome to the forum, unfortunately your going to need to supply more information of your application. Are we talking an RF antenna, a cell phone antenna, ethernet or some other application. In RF there are considerations that ethernet does not need to worry about as one example
     
  4. Jul 11, 2013 #3
    RF antenna, I apologize for my lack of information.
     
  5. Jul 11, 2013 #4
    ok not much more information, but enough to get the discussion going.

    In RF you want an amp that is designed for RF, I recommend looking here

    http://www.analog.com/en/rfif-components/rfif-amplifiers/products/index.html

    for the antenna, you need low loss 50 ohm coax cable, for short runs use RJ-58. keep the number of connectors at a minimal, do not have excess wiring to the antenna. Each connector has approximately 1/2 bd loss. This is a rule of thumb in RSSI calculations, (connectors are typically less loss).

    Another consideration many forget is that you will be transmitting a frequency, you will need to make sure that, that frequency does not interfere with local RF systems. In Canada the frequency assignments are regulated through Industry Canada. I do not know the regulatory RF body in the states.

    The antenna itself is designed in a manner to increase gain, Each antenna is designed to operate at a specific frequency range, factors suchas the number of windings, a compared to the inner metal material, or dipole and length oe antenna itself on the whip style antenna's determine its optimal operating frequency. I would recommend looking pre designed antenna's for the frequency your working at.
     
  6. Jul 12, 2013 #5

    Baluncore

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    I presume you want to maximise the voltage so you can rectify it with the diode to extract the power. The answer is that you need a high impedance antenna, probably with a 300 or 600 ohm termination such as a tuned loop, rhombic, Sterba or Bruce array. You need the biggest possible antenna to intersect the maximum power.

    You will get the lowest voltage drop with germanium diodes, but these days a synchronous detector made from MOSFETs will actually do better. Start with silicon diodes, they are cheap and more robust.

    It is important that you do not tune to aircraft or shipping navigation beacons as your antenna (when tuned properly) will modify the radiation pattern and so distort the radiated field. You should also be aware that you can get RF burns from such circuits if a powerful transmitter is nearby.
     
  7. Jul 12, 2013 #6
    Thank you sooo much Baluncore and Morded. I apologize for not being as specific as possible but I have little technical knowledge.

    Where would I procure a high impedance antenna?
     
    Last edited: Jul 12, 2013
  8. Jul 13, 2013 #7

    sophiecentaur

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    So far, you do not seem to have mentioned the operating frequency. This is the most important thing to know before selecting or designing an antenna. What is the purpose?
    If you are just asking about the best form of diode to use, could it be that you are planning a simple 'crystal set'?
    More details of what you actually want to do will get you some much more useful answers.
     
  9. Jul 13, 2013 #8
    Where to buy high impedance antennas would be sufficient.
     
  10. Jul 13, 2013 #9
    The best antennas (delivering most voltage output for a given RF signal strength) are not available from a single company, but are procured via competitive bits with multiple contractors typically involved and cost millions of dollars. http://en.wikipedia.org/wiki/Very_Large_Array

    How deep are your pockets? Why not at least share with us what frequency you are considering?

    If you are actually planning to spend money and try to build something I suggest you share more about your goals. There are lots of folks here who can help you steer around the multitude of landmines encountered when attempting to build a radio.

    Cheers
     
  11. Jul 13, 2013 #10

    sophiecentaur

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    Are you aware of what you are asking here? The impedance of any antenna will depend upon the frequency it is operating on. An 'antenna' could be 2cm or 2km in extent , and anything in between, depending on various factors.
    If you want an answer then you will need to ask the correct question. :smile:
     
  12. Jul 13, 2013 #11
    I don't need an a very large array or those big antennas. I just need one to build a rectenna.
     
  13. Jul 13, 2013 #12

    sophiecentaur

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    What frequency???
     
  14. Jul 13, 2013 #13

    Baluncore

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    The design of your system requires us knowing what you aim to do. You appear to be reticent to communicate your aims. If you are trying to recover energy transmitted by yourself then you have control of the transmitter frequency and the power radiated. In that case you should maybe first Google “Rectenna” to familiarise yourself with the field and the availability of commercial “off-the-shelf” components.

    If you are trying to harvest energy from a local transmitter then you will need to know the frequency of that transmitter. We really cannot help you unless you tell us an approximate frequency. You should also research what laws in your country apply to energy theft. It is a trivial exercise for enforcement officers to locate a significant RF power sink in their antenna radiation pattern. That could prove more expensive to you than your investment in equipment.

    Please state your aims.
     
  15. Jul 13, 2013 #14

    jim hardy

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    2016 Award

  16. Jul 14, 2013 #15

    sophiecentaur

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    No doubt there is a copy available in your favourite local surplus store, eh Jim? (Buried amongst the cables and whatnot.) :biggrin:
     
  17. Jul 14, 2013 #16

    jim hardy

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    That's where you find them. I have about four of varying antiquity. :approve: :biggrin:

    btw where do you get those smileys? I pasted 'biggrin' from your post...
     
  18. Jul 14, 2013 #17

    dlgoff

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    Reply with "Go Advanced".

    attachment.php?attachmentid=60280&stc=1&d=1373829687.jpg
     

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  19. Jul 14, 2013 #18
    I can't divulge the exact details of what I am building, but the frequency is 154.96500.
     
  20. Jul 14, 2013 #19

    sophiecentaur

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    That didn't hurt, did it? You see, we could have been discussing anything from long wave to microwaves. So you are after a 2 metre antenna. Why not buy one off the shelf? You seem to know very little about RF so you have the best chance of a good solution if you get yourself a good Marine VHF antenna. (Quarter wave monopole)
    If you want to get clever and build your own, then look on Ham Radio sites. They are chock full of antenna designs that people have actually made at home.
     
  21. Jul 14, 2013 #20
    I would advise you check your local frequency regulations. In some areas that frequency has regulated uses.
    Unfortunately I live in Canada here its controlled by Industry Canada. For the states I do not know.
     
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