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howdo i tune my antennas?

Discussion in 'Communication (CB | GPS | HAM)' started by bigoltrux77, Aug 23, 2002.

  1. bigoltrux77

    bigoltrux77 1/2 ton status

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    i have a dual 5ft firstik antenna setup on my mirrors. Ive always wondered how in the heck i tune them. I know you screw the tops in or out. but thats all i know. any help?
     
  2. Z3PR

    Z3PR Banned

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    Cophasing on a Blazer just won't work properly. You need 9 foot between the antennas for cophasing to work right. I would recomened getting a new coax for a single antenna. You can leave the other one on for looks. To tune it, first check SWR's. If your antenna has tunable tips, adjust up or down for lowest SWR reading.
     
  3. bryguy00b

    bryguy00b 3/4 ton status

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    what exactly is SRW?
     
  4. Z3PR

    Z3PR Banned

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    To my understanding, (and I could have it wrong) Standing Wave Ratio (SWR) is the radio's output power that doesn't make it out the radio's antenna system. I'm sure someone could explain it much better then I. I do know that if your SWR's are to high, it will damage your radio. I've blown finals in a radio by transmitting with SWR's over 3.5. Hope this helps you.
     
  5. bryguy00b

    bryguy00b 3/4 ton status

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    ahh ok gotcha..as long as i know what to look out for there now..lol thanx!
     
  6. Z3PR

    Z3PR Banned

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    High SWR's will also cut down on the preformance of your radio. I personally want to get the most out of my radio equipment. I'm willing to give up looks for preformance. Thats why I went with a 102" mounted over the cab. Doesn't look as cool as a pair of antennas off the mirrows, but works alot better !!!!
     
  7. bryguy00b

    bryguy00b 3/4 ton status

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    yea..well im after looks and function..actually more looks than function..(to be honest with you i bet i wouldnt even use it all that much) but when i do i want it to at least work right ya know..
     
  8. Z3PR

    Z3PR Banned

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    Then I would recomend a pair of K40 trucker antennas. They'll look cool, and preform the best in my opinion. If you look at my post "Bigfoot Radio Repair" in this forum, click on the link, under new products you can order the K40 antennas. And Bigfoot Radio Repair beats MOST everyone else's price on them. /forums/images/icons/grin.gif
     
  9. Z3PR

    Z3PR Banned

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  10. bryguy00b

    bryguy00b 3/4 ton status

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    sweet thanx!!
     
  11. Z3PR

    Z3PR Banned

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    Glad to be able to help. /forums/images/icons/grin.gif
     
  12. calcide

    calcide 1/2 ton status

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    I don't know much about CBs, but I've worked with RF equipment for a while... SWR, Standing Wave Ratio, is the ratio of forward and reflected power. Forward power is the power coming out of your radio, reflected power is power that the antenna does not radiate and is being "bounced" back into the output of the radio. This is bad for the radio and also wastes your power. High SWR is created by your antenna not having the same impedance as the output of your radio. Every antenna should be tuned for the radio it's being used with, since the output impedance varies. The antenna is tuned by changing it's length. SWR can be measured with an SWR meter, or with a directional power meter. With a directional power meter, you measure the power in each direction, then compute SWR. This way is better, since you can also tell how much power you are really putting out.

    In the real world, SWR is called VSWR and is a calibrated parameter on RF attenuators, directional couplers, etc.
     
  13. The_Sandman_454

    The_Sandman_454 1/2 ton status

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    It's my understanding that SWR is best set 100% independantly of the radio being used... Such as with an antenna analyzer like MFJ makes... /forums/images/icons/crazy.gif If you set that antenna at the proper resonant length then it should be just fine regardless what radio is being used if it's being used on the frequency it's set to...

    Seems to be quite a few people I recall hearin' that from...
     
  14. Z3PR

    Z3PR Banned

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    My friend Lew has one of those. Cost over $200.00 for it. Nice tool, but too pricey for something I wouldn't use that often. We did use it on my Blazer when we mounted the 102.
     
  15. calcide

    calcide 1/2 ton status

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    Re: howdo i tune my antennas? *DELETED*

    Post deleted by calcide
     
  16. rebelk5frk

    rebelk5frk 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    It doesn't matter how good the radio manufacturer is, the output impedance will not be identical from radio to radio

    [/ QUOTE ]

    That's not quite totally true. All radios are tuned to be 50 ohm output. Now depending on the manufacturer it may be tuned better than some. Any radio that has been properly tuned by a decent tech will be 50 ohms output..

    An antenna isn't tuned to the radio.... it is tuned to the frequency being used while attempting to keep the impedance at 50 ohms.

    For very specialized installations (not pratical by any means for most people) you can actually tune the output of the radio to a specific antenna impedance. (btw most mobile whips aren't actually 50 ohms)
     
  17. rebelk5frk

    rebelk5frk 1/2 ton status

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    If you're after looks AND performance then you might actually get better results using only 1 antenna. Like it was mentioned earlier dual antennas don't work properly on a blazer due to the small distance between mirrors.

    If you really want the look of duals and don't mind spending the extra money for it then go ahead and mount both of them but instead of using the co-phase coax cable, hook a single coax cable to just one antenna and tune the live antenna for best results. The second antenna will have very little effect on the transmitted and received signal. The live antenna will actually perform better than using a dual setup.
     

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