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How do I calibrate SWR with a non-adjustable antenna?

Discussion in 'Communication (CB | GPS | HAM)' started by mofugly13, Jan 31, 2005.

  1. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    I just installed a uniden 510xl in my Samurai. I went the chap route and got an old mirror mount, and bolted it to the body. Then I got a fiberglass antenna that used to be on my dads jeep, and used that. When I hooked up my dads old Radio Shack SWR meter, it was reading past 3. There is no adjustability built into the antenna or the mount. How do I calibrate the SWR with this setup. My girlfriend let me try an old Pacer antenna she scored for free, and it has an adjustable tip, I was able to get the swr down to 1.2. But she wants her antenna back. Am I resigned to buying an antenna with some adjustment built into it? My pops used the non-adjustable fiberglass antenna for years with no probs, but i want to do this right. C'mon Z3PR, I know you have the answers I need.

    Along the same lines, I have a 102" stainless whip that I plan on mounting to the K5 when I get to that. It doesnt have any adjustability to speak of. How would I go about calibrating this when I plan on using it? Is there some sort of special mount with some adjustability built into it?
     
  2. Z3PR

    Z3PR Banned

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    Check the base of the antenna. On most antennas there should be a couple of set screws. You can loosen those up, slide the antenna up or down too adjust the SWR's. But in all honesty, a radio is only as good as it's antenna. If you don't have room for a 102", then consitter getting a K40 or Wilson 5000. Also make sure the mount is grounded good. If need be, you can always run a grounding strap from the mount to the frame.
     
  3. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    Yeah, I understand how an antenna "should" be adjusted, problem is, there is no set screw or anything on the antenna I want to use. I dont believe it is a cheapo antenna, 'cause my dad usually sprung for quality stuff. I read the antenna adjustment stuff on firestik's site (that you linked to in another post). Looks like I'm supposed to figure out if I'm electrically "long" or "short" and then add length or subtract length from the antenna conductor. I told my dad about the prob, and he gave me three 2' "center loaded(?)" antennas, which do have adjustability in them. They look kinda wimpy, though, as far as driving through brush, low branches and whatnot. It will be awhile 'till I'm back in the mountains where the Sammi is. I guess I'll double check my ground and fiddle around with the other antennas. What does a K40 or a Wilson 5000 go for? Are the firestik antennas still the sh!t?
     
  4. rebelk5frk

    rebelk5frk 1/2 ton status

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    If your SWR is around 3:1 then you have a bigger problem. Something like the antenna not having a ground, bad coax, antenna too close to the body if it's on the bumper etc.

    Once you find the major problem, the SWR should drop quite a bit. If you still need to fine tune the antenna you should probably be able to adjust it. I don't think you ever mentioned what type of fiberglass antenna you have. (there are a couple of types) If it is the "firestick" kind where there is wire wrapped around the fiberglass core then surrounded by plastic/rubber then you should be able to pull the cap off the top and cut the wire if needed.

    As for adjusting and/or tuning 102" steel whips, you normally don't need to do any adjustments. Every install I've done the SWR was well below 1.5:1 unless it was being used for a different band than what they are designed for. I've cut a few down for use on 50-54Mhz (6 meter ham band) using a hack saw, tin snips, cut off wheel, etc.

    BTW I've seen the Wilson and K40's sell from $30 to $80 depending on which model and where it was being sold
     
  5. Z3PR

    Z3PR Banned

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    Does you Samurai have the swing out spare tire carrier ??? If so, try mounting your antenna off it. Make sure you scrape the paint off so the mount can get a good ground.
     
  6. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    The Sammi does not have the swing out carrier. I used a mirror mount that came with my GF's antenna. I only used the front half that the antenna mounts to and I bolted that with four screws to the body right in front of the rearview mirror. I scraped paint away from the body first for good ground contact. When I tried my GF's 'Pacer' antenna with the adjustable tip, I was able to get good SWR readings. The old antenna I am trying to use has no markings, so I don't know what brand it is. It's fiberglass with a fiberglas wrap up to the tip. I'll probably just go but a new antenna, but next time I'm in the hills, I'll fiddle with it a bit and see what happens.
     
  7. Z3PR

    Z3PR Banned

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