Cb setup tips. All help/info welcome

Discussion in 'CB Radio Forum' started by PotholeMcBounce, May 11, 2021.

  1. craig_sez

    craig_sez Road Train Member

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  3. Lowboy456

    Lowboy456 Light Load Member

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    I'd have to study up on it a bit more to understand the r's and X's.
    I think r is ohms or resistense and I have no clue what the X is?
    Is the x also refered to as jX? I've been looking into it already.

    I think I will try a strait to the battery connection as someone suggested earlier. I pick up a lot of buzz from power lines, my phone charger when its plugged in and my 12v fan.
    I use a 12v fan and the windows down while I heat my lunch on the defrost.
     
  4. BigJim63

    BigJim63 Bobtail Member

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    A lot of that noise comes in through the antenna.
     
  5. jdchet

    jdchet Light Load Member

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    And that's where the fun (heartache!) really begins!
    Easiest way to figure out where noise is coming from is to disconnect the coax from the radio and see if the noise goes away. If it does you have eliminated any concerns about noise coming through you radio power feed. When you reconnect your coax, just connect the center pin and see if noise is still present. If not, and the noise returns when you connect the outer part then you most likely have common mode interference.
    Now the wonderful task of chasing down the sources of your noise begins! I've found the easiest way to eliminate Cellphone charger noise is use the USB port on your AM/FM radio (if your radio has one) to charge your phone. Usually alot less noisy. Ferrites on offending noise source power lines can help, as well as a choke at the feed point of your antenna. Aftermarket LED headlights are also a big problem too! Another big offender is modified sine wave power inverters, if you have one.
    This web site, KØBG.COM is a really good read regarding mobile installs as well as this thread on another forum. MOBILE INSTALL: 579 Peterbilt
    In my recent experience some of today's big radios have some really "hot" receivers but seem to lack the proper filtering to go along with that "hot" receiver!
    Good luck!

    JD
     
    handlebar Thanks this.
  6. Night Stalker10

    Night Stalker10 Road Train Member

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    The X is called reactance. Some refer to it as resonance or even resistance which is wrong. Per webster reactance is:

    The opposition of inductance and capacitance to alternating current, expressed in ohms: equal to the product of the sine of the angular phase difference between current and voltage and the ratio of the effective voltage to the effective current.
     
  7. Lowboy456

    Lowboy456 Light Load Member

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    Ah ha ha! One more monkey wrench in the gears.
     
  8. Ridgeline

    Ridgeline Road Train Member

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    Just a few thoughts. These are just random thoughts, not explanations of how it all works.

    I said swr, resonance and so on don’t mean a antenna system is working.

    what I mean is the system is made up of three elements, the radio, the feedline (coax) and the radiating elements <<< notice this is plural.

    using an antenna analyzer (AA) is a great thing but it taking in account that this is seeing the feedline first then one HALF of the radiating element.

    Not both half’s.

    so when I look at a problem with an antenna on a mobile, I look at the other side of the radiating element, aka the rf ground. This has to be balanced, and hard to determine.

    you have to have both sides of the signal to get out, the longer of one has to have the same rf length.

    Ok so craig can step in and discuss dipoles on trucks, I only did a couple of these and they worked well, not perfect but well.
     
  9. jdchet

    jdchet Light Load Member

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    I think this would somewhat explain the decent, not great, readings I had when I hooked up my AA-35 analyzer to the OEM Freightliner Evo in the roof antenna. It won't hurt the radio, but it won't work worth a #### either!
    aa 2.jpg

    JD
     
  10. Night Stalker10

    Night Stalker10 Road Train Member

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    Yup, your X (reactance) is high, due to the lack of a proper RF ground that the antenna system needs in order to work to its best ability.
     
  11. craig_sez

    craig_sez Road Train Member

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    Nope...Dont know enough about the workings of a dipole other that the two pieces of a dipole need to be equal while 1 is the positive and the other is the negitive.
     
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