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high swr

Discussion in 'CB and Export Equipment and Accessories' started by butch, Feb 13, 2012.

  1. butch

    butch Member

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    hi all really enjoy the fourm this is my first post so please be paitent, well anyways i have a Magnum 257 hp in my pickup paired with a TNT 350 hd amp and a roof mounted Wilson 5000 roof mount antenna it works great with flat swr but as soon as i turn my amp on it jumps up over two the only way i have been able to get it down to a good level is install a TVI low pass filter between the Radio and the amp does this sound right does this mean the radio is splattering also i have the radio turned down to a 1.5 watt dead key


     
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  2. vo1ks

    vo1ks Active Member

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    SWR remains constant regardless of power. I suspect when you put on the amplifier there are excessive harmonics and other spurious signals present. Those are creating high reflected power which present themselves as high SWR.
     
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  3. 9C1Driver

    9C1Driver Well-Known Member

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    You have great equipment, I am concerned though that the HP version of the 257 is alittle too hot for that 2 pill amp. You might make sure on AM you dead key 3 watts, and keep the peak input at 35-45.

    Assuming your install is proper as far as antenna and grounds, make sure you have a 6 or 9 foot jumper. Are you re-calibrating the meter each time? I would skip putting anything between the radio and amp but a jumper.
     
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  4. butch

    butch Member

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    thanks for the replies yep i suspect spurious emissions too i have tried everything you said but the only way a can get the swr down is to install a low pass filter between the radio and amp. oh and yes i recalibrated my meter for the higher power level have been pulling my hair out for the last three weeks trying to get this figured out
     
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  5. 9C1Driver

    9C1Driver Well-Known Member

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    Where did you get the radio and was anything clipped?
     
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  6. mackmobile43

    mackmobile43 Jock Supporter

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    The filter normally goes after the amplifier, what brand of external meter are you using?
     
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  7. W5LZ

    W5LZ Crotchety Old Bastard

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    ... a more likely answer to that SWR problem is a simple mismatch in impedances between radio/amplifier, and/or amplifier and antenna.
     
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  8. bob85

    bob85 Supporting Member

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    vo1ks gave the most likely answer,
    to change swr you must change the load or introduce frequencies that are not where the antenna is tuned for,

    an unconditionally stable amplifier who's output impedance is not 50ohms does not cause high swr on a line with very low swr (50 ohm line terminated with a 50ohm load)

    amplifier input tuning effects swr on the jumper from radio to amp,

    detector diode none linearity can cause swr readings taken at the radio end of lossy lines to go up with increased output power but true swr stays the same.
     
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  9. butch

    butch Member

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    hi all thanks for the replies i got the radio from Walcott CB nothing was clipped that i know of i have an Ameritron AWM-35 remote mountcross needle watt meter also have used Dosy 4000 meter as well
     
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  10. butch

    butch Member

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    oh and yes i understand the filter usually goes between the antenna and the amp but i have tried that with no luck just seems odd by the way the filter is an RF LIMITED LOW PASS TVI FILTER DF-3000 3KW PEP
     
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