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Radials for a MFJ-1795 antenna

Discussion in 'On the Road' started by KC7RC, Jan 3, 2020.

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  1. KC7RC

    KC7RC Ham Member QRZ Page

    I am attempeting to setup a MFJ-1795 vertical antenna, but want to keep it portable.
    The situaltion is I live in an RV park the area is concrete, I have a sturdy tri-pod mount for the antenna with a 8' mast.
    I read that I need ground radials for the antenna to maintain a good SWR. signal out, recieve in.
    The question is how long do the radials need to be, will they need to be ground (earth contact) ? or is there another way of creating a ground plane? What will the length need to be for the radials?

    Next if I roof mount the antenna on say a storage building 10' x 10' what are the radial requirements then?

    kc7rc Roman
    Eloy, AZ/Florence, OR
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page
    Rudy Severns, N6LF has given us a treasure trove of easy to read info on radials. Drink deep.

    Incredibly simplistic summary.
    You have two choices: 1. Elevated radials 2. Radials layed on ground.

    1. Elevated Radials
    Elevated radials are the most effective, but must be treated the same as a half wave dipole and tuned in the same way. One set should give good performanc, two sets should be quite good. You need a tuned set for each band.

    2. Ground Radials.
    Ground radials are detuned by ground proximity and exact length is not as critical as for elevated radials. One will get you on the air. Four should give reasonably stable tuning/SWR and good performance. Eight would be quite good. 1/4 wavelength would be a nice length to aim for (Again, read Rudy's articles for extensive discussion of trade-offs). bill.

    Comment: I see the MFJ manual mentions the tuning process for this antenna is quite exacting with 1/4 inch increments having significant effects. Good luck, and may your patience be sufficient! :)
  4. WA7EM

    WA7EM XML Subscriber QRZ Page

    I one in my garage attic. I layed down welded wire fencing across most of the attic floor as a radial "mesh". I envision like ground mounting a vertical across very conductive piece of earth. So, no "radial" is tuned, but overall it is a very complete ground plain
  5. KC7RC

    KC7RC Ham Member QRZ Page

    Thanks for the reply, it gives me more to lthink about

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