Adjustable ends for a dipole antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W0RIO, Jun 26, 2020.

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  1. W0RIO

    W0RIO Ham Member QRZ Page

    Last weekend, I was experimenting with a 40 meter dipole in the field. I had built and tuned the antenna at home,
    but the antenna center frequency was much higher at the remote location. Using available parts, I came up with
    this hack job for making an adjustable antenna.

    The two dipole elements are made of old RG-58 coax, the copper clamps are just common electrical components.
    The solid wire is #8 copper. The copper wire was bent through the ceramic egg insulators and could be fastened
    better on the insulators, but it held up well. What is missing are some zip-ties around the wire where it meets the
    adjusters.

    After a few tries, I was able to resonate the dipole on 7.030 Mhz using an MFJ 259 analyzer.

    DipoleAdjusters.jpg

    Here's the dipole with adjusters deployed in my "QRP shed". Despite the lousy band condition, I made a
    few contacts.

    Shack40m.jpg

    What other tricks have hams used for adjusting their dipoles? In the past, I've always had to clip a few inches
    off of each wire, and inevitably solder short lengths on the ends after cutting the antenna too short ;-)
     
    SM0GLD, KU3X, AK5B and 1 other person like this.
  2. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    With all due respect, I believe the height of the dipole was more of a factor than lousy band conditions.
     
    K0UO, SM0GLD, K7TRF and 1 other person like this.
  3. AE1N

    AE1N Ham Member QRZ Page

    Why mess around ... get a good tuner which will put yoo on all 11 bands (6m-160m)!
    ---Layne AE1N
     
  4. K1VW

    K1VW Premium Subscriber QRZ Page

    Good idea!
     
  5. W1VT

    W1VT Ham Member QRZ Page

    I use insulated wire and twist the wire together without removing the insulation.
     
    W6JJZ, W9WQA and WB5YUZ like this.
  6. W9KEY

    W9KEY XML Subscriber QRZ Page

    Make the dipole antenna wires a bit longer than you think they will need to be using Total Length (feet) = 468 / frequency in MHz (each side is 1/2 of that length). Fasten both wires permanently at the center insulator (connected to your feedline) in the normal manner.

    Using an insulator at each far end, gently and temporarily wrap the wire ends around the insulator (180 degree wrap) to set the wire element length and use a zip tie around the wire (and its pigtail) to hold it in place. Do the same thing with the other dipole end wire, insuring both legs are exactly the same length.

    Hoist the antenna to its operating height and check with your antenna analyzer (always measure at its intended operating height above ground).

    Lengthening or shortening the antenna is easily accomplished by simply sliding the pigtail end back or forth through the wire tie (assuming you haven't pulled the wire tie too tight). After the antenna is adjusted to a satisfactory length, you can twist the wires permanently around themselves at the end insulators, or just use another couple zip ties pulled tightly (with the understanding even black wire ties will fail in several years due to UV sunlight - twisting the wires is best).

    This method works perfectly with bare (and relatively stiff) antenna wire. When using insulated wire, you many experience somewhat less "adjustability" since the wire and its pigtail end are not exactly in direct contact (separated by the insulation and with some capacitive coupling). So be careful to use your antenna analyzer again when / if you eventually cut off the excess pigtail ends.
     
    K0UO and WN1MB like this.
  7. K7TRF

    K7TRF Premium Subscriber QRZ Page

    When I want to lower the frequency of a dipole already cut and don’t have enough wire folded back I just add end tuning stubs that hang straight down off the end insulators.
     
    AK5B, W9WQA and WN1MB like this.
  8. WN1MB

    WN1MB XML Subscriber QRZ Page

    Great hack, especially the readily available and cheap parts. I'm curious what length of #8 you used.

    Love the QRP shed. It reminded me of the ham shack shed the OT had in a book I repeated picked up from our little, local library as a kid. The book and story line was an important key to my early introduction to ham radio.

    Will you be operating from the QRP shed for FD this year?

    Surrounding terrain looks a bit desolate - at least to this New Englander more familiar with a multitude of trees and their canopy shade. Where's the shed?

    72/73/77, Jeff WN1MB SKCC 11128C

    Antenna height notwithstanding and with all due respect, I believe the OP's appraisal of band conditions, especially of late. Check out his QRZ page and personal website for a point of reference.
     
  9. W9WQA

    W9WQA Ham Member QRZ Page

    dont need #8 !! any wire...
     
  10. WN1MB

    WN1MB XML Subscriber QRZ Page

    OP said "Using available parts, I came up with this..."
     
    K0UO and AK5B like this.

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