High SWR's

Discussion in 'General Technical Questions and Answers' started by NA1SA, May 16, 2018.

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  1. NA1SA

    NA1SA Premium Subscriber QRZ Page

    I recently purchased a Cobra 29 for my shack. I mounted the antenna (a four foot Firestik) using a mirror mount on a 10 foot piece of galvanized pipe. I'm running a 50 foot piece of RG-8 coax between the radio and antenna and can not get the SWR's below a 4. Can anyone offer what the problem may be? I turned the tuning screw on the antenna from all the way down to all the way up and nothing I try gets the SWR's under a 2.

  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I'd guess if you add radials it will be much better. That's a mobile antenna intended for mounting on a flat horizontal surface like the roof of a car, truck or van.

    The larger that horizontal surface (its ground plane) is, the better it should work...and match.
    WA7PRC, K7TRF and K2WH like this.
  3. K2WH

    K2WH Ham Member Volunteer Moderator QRZ Page

    I agree with WIK but you could also have bad coax or you don't say what frequency the antenna is made for and what frequency you are trying to use it on.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'm with Steve, your RF return using a piece of galvanized pipe doesn't come close to emulating a vehicle's chassis. I'd start by adding at least a couple of radials approximately 1/4 wave each for the band and see if that helps you tune the antenna.
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    27 MHz.

    And the "Firestik" products are not very good to begin with.

    I've tested them for locals: On a scale of 1-10 compared with "other" CB antennas, they're about a 3.
  6. N7WR

    N7WR Subscriber QRZ Page

    No ground plane..that antenna on its best day (infrequent) requires a ground plane to form the other half of the vertical dipole. A piece of pipe doesn't get it. I guess antenna theory is no longer covered on the extra exam. Yep it is a CS comment but for an extra to not be able to figure out this simple problem is indicative of where the hobby has fallen over the decades.
    N3AB, WG7X and W7UUU like this.
  7. KP4SX

    KP4SX XML Subscriber QRZ Page

    "SWR's". :(
    N3AB and WG7X like this.
  8. ND6M

    ND6M Ham Member QRZ Page

    Look at his QRZ bio... you been trolled
  9. K1ZJH

    K1ZJH Ham Member QRZ Page

    A 100 foot run of RG-174 will reduce the SWRs.
  10. KB0MNM

    KB0MNM Ham Member QRZ Page

    We can only take a question at face value. Since he shows an MFJ-259C and several homebuilt antennas ( on the page here on QRZ ); I would suggest that he consult the MFJ-259C manual.
    ND6M likes this.

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