Ultralight Portable Antenna Quest

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC8VWM, Jun 18, 2017.

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  1. KC8VWM

    KC8VWM Ham Member QRZ Page

    So the antenna design criteria is to construct a portable ultralight vertical antenna suitable for SOTA or backpacking in the wilderness.

    ...The antenna must be very lightweight. Under 1 pound !

    ...The antenna must be very small in size to carry around and take up very little space.

    ...The antenna must cover at least 9 bands!

    ...The antenna must perform very effectively and efficiently.

    Hmmm... This sounds like some kind of magical antenna design that doesn't exist.

    ...or does it?

    Introducing the portable ultralight multi band antenna.

    IMAG0443_zpspjcny1b3.jpg

    Not much larger than 3 dollar bills long, this antenna will cover 2m through 40m and will perform very efficiently on all these bands. It will be the perfect portable antenna companion for an FT-817 while travelling anywhere.

    This antenna is a full 5/8 wave antenna on 2m and 6m bands for maximum gain and performance.

    It is a full sized 1/4 wave antenna on 10 and 12 meters. (no loading coil needed)

    So how does this small portable antenna fair in terms of efficiency on bands like 14 MHz though?

    [​IMG]

    Not bad at all really. :) We are going to use this antenna as an inverted L configuration on the 40m band so efficiency should approach 90 % (more on that later.)

    So how does this antenna meet our criteria as a lightweight portable antenna?

    IMAG0459_zpsps0h6kkc.jpg

    Yup that's only 0.8 Lbs. This antenna covers everything from 2m - 40m and weighs just 12.8 ounces !

    How it works?

    For 2m operation the antenna element is telescoped to 4' (5/8 wave long) and the coil is used as a matching network for the antenna. The antenna taps are movable to achieve the best SWR reading.

    On 6m the antenna element is extended to 1/4 or 5/8 wave long and the coil is tapped and used as a matching network.

    On 10 meters the very top section of the telescopic whip is collapsed and not used. This is now a full sized 1/4 wave antenna. The coil is entirely bypassed by joining the red and blue wires together and this provides a less than 1.5:1 SWR on 10m.

    For operation on 12,15,17,20 and 30m you tap the coil at various locations marked on the coil:

    The blue wire remains at the same location for all bands but it remains adjustable if desired.

    The red wire taps the yellow paint mark locations on the coil to work other bands down to 30m.

    IMAG0671.jpg

    On 40m you tap the coil at ""40 / 12" and attach one of the radial wires approx. 20 ft. long to the top of the antenna and then run it in an inverted L configuration away from the top of the antenna. This provides an SWR of 1.2:1 on 7.200 and 2:1 at 7.050.

    Construction of the antenna:

    The antenna is going to be based on a lightweight fishing pole design approx. 12' long. Carefully remove all the fishing line guides from the pole sections as we will no longer be needing them. They are glued to the fiberglass rod and will break free if carefully rocked back and forth. Then remove the cap at the bottom of the fishing pole and remove all the individual telescopic sections and put them aside.

    Next remove any metal clamps typically used to hold the fishing reel in place on the fishing pole handle. A dremmel tool or similar method can be used to cut them off the pole handle.

    The Inductor coil is going to wrapped on low cost (and lightweight) automotive split loom tubing like this:

    [​IMG]


    The fishing rod handle itself is going to be used as the coil form. Place the automotive loom tubing around the fishing pole handle. This will result in an approx. 1" diameter coil. Wind some #14 AWG bare solid copper wire - 30 turns around the split loom tubing. (room remains available to add more coil turns if desired.) you may run some hot glue along the coil to hold it's shape in place to prevent it from slipping out of the automotive loom tubing grooves if desired.

    When completed, the wound coil should look like this:

    IMAG0439_zpssodfxdzr.jpg

    Next we install an SO-239 connector on the fishing rod handle.

    There is a small piece of aluminum which is bent into an L shape. It is screwed directly to the S0-239 connector and then the other side of the L bracket is placed under the hose clamp as shown in the photo below. This holds the connector quite securely in place.

    IMAG0450_zpsoq4y4iad.jpg

    Next connect the end of the coil wire to the SO-239 connector. Install a screw and some washers and then connect the coil wire between the washers on the screw as shown below.

    IMAG0451_zpst0a453pk.jpg

    Install another screw on the SO-239 connector and install a wing nut as shown above. This will serve as your antenna radial attachment location. Solder the blue wire to the center pin of the SO-239 connector. I am using a curved blade connector from an Anderson power pole as a coil tap, but you may decide if an alligator clip would work better.


    The wire chosen for the tap should be "rubbery and very flexible." Avoid using stiff wire for your coil taps. The length of the wire should be long enough to reach the entire length of the coil.

    IMAG0447_zpshmhhkb6g.jpg

    Tuning the coil depends on your particular fishing pole length and other factors. It is primarily done by experimenting with tapping different locations on the coil. When you find the sweet spot on the coil for the desired band, achieving the best SWR, then mark it with a paint marker.

    The red wire is attached to the telescopic fishing pole side using a hose clamp. But wait a sec... the fishing pole is made of fiberglass and this doesn't make any sense at all though..?!?! :D

    Yes it does and here's why...

    Remember those individual pole sections I told you to remove from the bottom of the fishing rod and put aside for later?

    Well those fishing pole sections are going to be individually wrapped in aluminum tape as shown below.

    IMAG0454_zps8be5rt6v.jpg

    It is required to cut the aluminum tape using a box knife to size the tape for a good fit. Carefully wrap the tape on the fiberglass tubing sections ensuring there are no wrinkles in the tape. It helps to use a cloth to rub the tape perfectly flat. It's a little bit like installing window tint on glass, but I completed all the sections in a little over an hour.

    IMAG0445_zps3ljedgzp.jpg

    Be sure to fold over a little bit of aluminum tape on the inside of the fiberglass tubing at the ends of each section. This will ensure electrical conductivity occurs throughout the entire telescopic antenna.

    What you have now is the world's lightest all aluminum telescoping antenna!

    IMAG0446_zpsoecua2xh.jpg

    So now we need radials for our antenna.

    The wire I am using was extracted from a 6 conductor telephone extension cord. This wire is really flexible and doesn't tangle very easily. Telephone wire is actually very easy to work with because of the high strand count.

    So i made up 6 antenna radials approx. 22 feet long to use with out vertical antenna.

    The bag attached to the handle as seen in the first photo is intended for safety glasse,s but it was re-purposed for holding all our antenna radials inside. It can also contain printed setup instructions for using the portable antenna if you like.

    So there you have it...

    An ultralight multi-band portable vertical antenna you can only build yourself and money can't buy. :)

     
    Last edited: Feb 17, 2018
    VK4HAT, AE4LH, KA2CZU and 7 others like this.
  2. WG8Z

    WG8Z Ham Member QRZ Page

    Awesome Charles
     
    KC8VWM likes this.
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    I normally hate to be flippant, but I can empty my Cantenna of all oil & it won't need any silly wires. Efficiency is great, if you consider energy to heat conversion & low wattage.... No tuning.
    Good morning, Charles. I figured I'd get this out of the way early...

    Ed
     
    WD0BCT and KC8VWM like this.
  4. KC8VWM

    KC8VWM Ham Member QRZ Page

    Good morning Ed. :)
     
  5. KC8VWM

    KC8VWM Ham Member QRZ Page

    Thanks Greg. If I had an extra one laying around, I would give it to you. :)
     
  6. AK5B

    AK5B Ham Member QRZ Page

    This is EXACTLY what the late James Bond (G007JB/S5, 6Y, C33, etc., etc., SK) would have chosen had he been able to be active during some occasional down time while on various assignments in exotic lands (G007JB/S5, 6Y, C33, etc.). He could have kept in touch with Miss Moneypenny from just about anywhere with the KC8VWM Cattle Prod/Walking Stick/Jousting Pole Magic Wonder Featherweight Antenna!

    Knowing James, he would have cleverly concealed it in a box of cigars or disguised as a brolly handle. The radials might have been substituted with stiffer wire, though---to serve as a handy garotte in the frequently dire situations that he was especially prone to encounter.

    Now we know why you were inquiring about coil tapping methods the other day. Brilliant, Charles!
     
    KC8VWM likes this.
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    James would have just used an umbrella, because it already has a cap hat & can fire bullets...

    Ed
     
    KC8VWM likes this.
  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Well done, Charles.
     
    KC8VWM likes this.
  9. AK5B

    AK5B Ham Member QRZ Page

    But those bullets made it exceed the weight limit, didn't they?
     
  10. WA4SIX

    WA4SIX Ham Member QRZ Page

    Obviously, Q would use .22s...

    Good work, Charles. I'm liking what you are doing.

    Ed
     
    KC8VWM likes this.

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