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Antenna Tuners....Yea or Nay?

Discussion in 'CB and Export Equipment and Accessories' started by Eastside, Sep 24, 2011.

  1. Eastside

    Eastside Well-Known Member

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    I have never owned one....and do not know much about them...only that they somehow give you a flat match on channels you would not have a flat match without the tuner....one guy I asked about them said they are junk...that they just fool the radio....anyway what say ye?


     

  2. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Antenna couplers have their uses.

    I have been playing with wire antennas lately. Feed them with 450 ohm ladder line.

    Antenna coupler is a must on this type of set up if the antenna will be used for multiple bands. Matches the antenna's feed point impedance to 50 ohm so the transceiver will be happy.
     
  3. towerdog

    towerdog one-niner-seven

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    the match the impedance of a mismatched antenna, but also dissipate reflected power in the form of heat. its similar to the concept of a loading coil, allowing a shorter length of antenna to act like its resonate.

    I cant see any reason to run an antenna tuner on the 40 CB channels, or even the upper and lower outband channels. Tuners are used more by ham operators to use the same antenna on different HF bands, especially in a mobile setup.

    You use a tuner to make an antenna cut resonant on say, 20 meters to become resonant on 10meters and 40 meters, and barely work on 80. Its more about just making it work than making it work better.

    remember, if its not resonant at the transmitting frequency, power reflects back to the radio, too much power, your finals burn out, your mic shocks you or your neighboors call the FCC over TV interference. Not to mention power is wasted that should have been transmitted.
     
  4. Robb

    Robb Yup

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    If you are a CBer using antennas made for the CB band, then tuners have no real value to you as yet. If/when you get a Ham license, then antenna tuners become a tool that is used. Not saying you can't use a tuner as a CBer; but when commercial antennas are available that are tailored, tuned, and built specifically to use on CB - then using a tuner has little use if the SWR has been adjusted correctly. Commercial CB antennas are built to be resonant for the CB/'11 meter' portion of available radio bandwidth.

    To understand 'antenna resonance' one might ask the question: why is a 1/4 wave CB antenna ~9 ft and a 1/2 wave CB antenna ~18 ft?
    Ans: Because one whole wavelength on the CB band is ~36 ft; so 1/4 of that will be 9 ft and 1/2 of that will be 18 ft.
    Antenna length dictates the frequency that the radio can use to distribute radio freq power. The 1/4 and 1/2 are used because they are harmonic intervals of that freq. 5/8, 3/4, and even 7/8 intervals of 36 ft can also be used.

    Because the electrical length of the ~27mhz (the 'CB band' freq in megahertz - or 'mhz'). It takes that much length of wire/metal to radiate that freq in 'harmony' with the transmitted signal. As the length s adjusted, it can be dialed in to be most resonant and the SWR will be lower. It needs to be adjusted differently to reach this harmony so that the SWR becomes acceptable along with resonance; this is just an oversimplification. Harmony might not be the best word to use; but it is a starting point to understand the concept.

    As previously said, Ham operators will often make their own 'wire dipole antennas' that may require 450 ohm feed line instead of 50 ohm coax used for CB. These antennas will be used for many bands on many frequencies (often from 4mhz thru 28mhz) for which these antennas aren't resonant - like a commercially made CB antenna is. So they require incorporating an adjustable variable capacitor and inductor coil - which is all an antenna tuner is - so that they will change/'tune' the dipole antenna's impedance so that the radio will see 50 ohms impedance.

    If you can understand that; then you are starting to understand one aspect of what Ham radio requires!
    You've asked the right question.
     
    #4 Robb, Sep 24, 2011
    Last edited: Sep 24, 2011
  5. Eastside

    Eastside Well-Known Member

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    So they are good for making a antenna into a multi band antenna eh?
     
  6. W5LZ

    W5LZ Crotchety Old Bastard

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    A tuner is nothing but an variable impedance transformer. It changes whatever the impedance is from the antenna system to 50 ohms that the transmitter want's to see. It's just like using a voltage transformer to convert 120 volts to 12 volts, except it's changing impedance, not voltages.
    If you can make the antenna system's impedance 50 ohms without using a tuner, then that's good. If you can't, then using a tuner is certainly better than putting up with a terrible SWR, as far as the transmitter is concerned. Mainly because it will mean the transmitter isn't 'cutting-back', it's still putting out full output. If there's SWR between the feed line and the antenna because of an impedance mismatch, then it's still there. That mismatch can result in less power being radiated, not because the transmitter can't/won't produce it, but because of that feed line/antenna mismatch.
    - 'Doc
     
  7. Robb

    Robb Yup

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    Not always. It depends on the antenna and how it is constructed. What I pointed out are generalities; there is more to it than that. But that is a starting point in simplest of terms.

    An Imax 2000 or an Antron A99 have a built-in capacitor and coil that allows them to work fairly close to five Ham bands (6, 10, 12, 15, and 17 meters) and the CB band as well. But using a tuner to make up for the slight impedance difference allows those antennas to be used by Hams (I use an Imax 2000 with a tuner). Not all antennas can do that. A 1/2 wave CB aluminum ground plane might be able to do 10 and 11 meters WITH a tuner ('CB'); but not the others bands mentioned as the the A99/Imax 2000 can do. Construction differences dictate limitations as well as strengths too.

    Hams use the term '10 meters' or '6 meters' or '40 meters' - because the length of the wave to those frequencies are 10 meters = ~33.2 ft and 6 meters = ~20 ft and 40 meters = ~132 ft.

    As the frequency used increases; then the length of the antenna decreases.
    As the frequency used decreases; then the length of the antenna increases.

    Some Hams operate on 160 meters; how long is a dipole for that frequency if a dipole is 1/2 the length of that frequency?
    Ans: 80 meters - or ~265 ft.
    Each half if the dipole is ~132.5 ft; because a dipole uses two 1/4 waves to make a 1/2 wave.
    The resonant frequency is ~1.8mhz.

    It all gets easier when you get used to it.
     
    #7 Robb, Sep 24, 2011
    Last edited: Sep 24, 2011
  8. Eastside

    Eastside Well-Known Member

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    Interesting stuff.......how long of a dipole do you need for the 11 meter band?
     
  9. Robb

    Robb Yup

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    OK.

    If we start with the given that the CB band of 11 meters to be ~36 ft; then the overall length of any dipole is half of the length being used - then it would be ~18 ft overall in length.

    Each half of a dipole would be one half of that - or ~9 ft.
    That is the approximate length; but close enough to understand the thought.
    To be more precise, the overall length of a CB dipole is ~17.2 ft and each half is 8.6 ft.

    The diameter of the wire used and the material is also a factor - too.
    Copper stranded wire (10 or 12 ga) will work close in this circumstance.
    Both ends of the dipole are trimmed equally until the SWR is close enough to 1.5.
     
    #9 Robb, Sep 24, 2011
    Last edited: Sep 24, 2011
  10. Eastside

    Eastside Well-Known Member

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    You think if you are experimenting with home brew antennas...it would be worth buying a tuner?
     
  11. Robb

    Robb Yup

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    Hams do it all the time - my man.
    Many CB guys build dipoles out of 1/2 inch electrical conduit so they don't have to support the ends.
    They support it in the middle with PVC pipe - as well as the vertical support too.
    Using two 10 ft pieces of electrical conduit @ ~$3 apiece cut to 8.6 ft lengths makes it cheep!
    Tune the SWR to 1.5 on ch 20 and then check it on ch 1 and ch 40 to see if is close.

    It doesn't have to be perfectly horizontal either.

    It is better to have a commercially made CB antenna tuned properly with a SWR meter if you have one already.
    They have already taken all of the variables into consideration.
     
  12. Eastside

    Eastside Well-Known Member

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    Yeah....I was thinking about making a dipole to shoot skip on the flatside....mebbe running a wire tree to tree. :D
     
  13. Robb

    Robb Yup

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    Just make sure that the ends of the dipole has insulators and the ropes supporting them are at least 5-10 ft away from the trees. If you make one out of conduit, you can also make it rotatable. No need for end support. Dipoles are directional by design; so it will make a difference how you have it pointed. They have transmit and receive 'nulls' or 'dead spots' coming straight off the ends of the wire. The sides of the dipoles are what radiate horizontally. 18 to 25 ft above any object is best.
     
  14. Eastside

    Eastside Well-Known Member

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    Yeah...I always made a dipole antenna for my stereo receiver....and I made one for my old Knight kit GCR. :)
     
  15. Robb

    Robb Yup

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    Nice!

    But any antenna that transmits needs to away from objects. Not on a wall. It needs to have free space. The more - the better.
     

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