Homebrew antenna using RC telescoping

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KX6MRN, Jul 15, 2016.

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  1. KX6MRN

    KX6MRN Ham Member QRZ Page

  2. K8JD

    K8JD Ham Member QRZ Page

    What are you trying to do with 28 inch telescoping whips? What band or frequencies are you thinking of?
     
    KX6MRN likes this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I've definitely used inexpensive telescoping whips in various antennas. They can work fine though many of the less expensive variety aren't that sturdy.

    I've used them mostly for portable and mobile HF antennas where I'd mount them above a loading coil and that up on a mast with the whole thing fed from the bottom. So basically a center loaded HF antenna where the telescoping whip is the uppermost element and can be adjusted to fine tune the antenna after coarse tuning it with a tapped loading coil or a single band loading coil.

    At 24" long the telescoping whip you linked could be used directly on 2m but you'd adjust it a bit short as in 19" or so. On lower bands you'd need some form of loading to get it to resonate but as mentioned above it could make a decent top whip to a center loaded antenna.

    MFJ makes some very long telescoping whips ~17' long and a few months ago there was an article in QST describing a clever rotatable dipole for portable use that was based on two of those back to back with a bit of PVC center support. The idea was that they tuned to 20m at near full length but then you'd tune to higher frequency bands by shortening both telescoping whips evenly. Nice concept.

    There's nothing magical about a telescoping whip other than the fact that it's easily adjustable via telescopic sections. So think of it as any other antenna element like a wire, traditional whip or section of tubing. So any antenna designs that use them are basically the same as antenna designs relying on other conductors but with the advantage of quick height adjustment for portability or easy tuning of overall element length.

    You can definitely incorporate something like that into many different antenna designs but the easiest are probably 2m whips which just requires mounting them to some form of ground plane or HF mobile antennas using base or center loading.
     
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  4. KX6MRN

    KX6MRN Ham Member QRZ Page

    Thank you both!

    I'd like to get a 2m or 70cm whip out of them if I can.

    This is good stuff. I had to get my mind straight in thinking about these as just any old wire.

    73's
    Matt
     
  5. KX6MRN

    KX6MRN Ham Member QRZ Page

    It turns out the ones I have extend to 38" :
    IMG_2594.JPG

    Should be a fun project... I hope with minimal frustration!
     
  6. W9GB

    W9GB Ham Member QRZ Page

    At 38" that whip would be a 1/2-wavelength at 2-meters.

    Yes. In the 1970s amateur radio magazines (CQ, Ham Radio, QST, 73)*, there were several DIY projects for a 2-meter antenna using replacement telescoping antennas (for automobiles, in 1970s).

    I still have that DIY Built 5/8-wavelength antenna (2-meters), based on a magazine article,
    using an adjustable whip.

    2 - 1/2" PVC caps
    1 - Short length of 1/2" PVC pipe
    1 - One short brass rod, with O.D. same as required for replacement telescoping antenna.
    24" - 14 or 16 AWG to wind coil (inside PVC housing)
    1 - PL-259 or 3/8-24 bolt (select desired for mobile/permanent mount)
    1 - Epoxy to lock in brass rod.
    1 - PVC cement for enclosure (once tuned)
    =====
    E.J. Bauer, W9WQ wrote about a different design (eliminating coil)
    in a later article for QST magazine.
    http://www.arrl.org/files/file/Technology/tis/info/pdf/8009022.pdf
     
    Last edited: Jul 15, 2016
    KX6MRN likes this.

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