Most Efficient Antenna for QRP

Discussion in 'QRP Corner' started by W7CJD, Dec 15, 2015.

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  1. W8ZNX

    W8ZNX Ham Member QRZ Page

    you were not asking for yourself
    then why are you taking the answers in such a personal manner

    ARCI 4203
    Last edited: Dec 17, 2015
    KU4X likes this.
  2. W7CJD

    W7CJD Ham Member QRZ Page

    If you are interested in sharing how you achieved an efficient antenna for portable QRP HF, that would be appreciated.

    I would like to hear about and see what others have done.
  3. KC8VWM

    KC8VWM Ham Member QRZ Page

    There are not many portable antenna's designed on the commercial market which offer this much "no compromise" and maximized performance ability, no antenna tuner capability, maximized band coverage capabilities and "instant" portability in such a lightweight package.

    It's probobly the best design as it can get as far as portable station antenna designs go...

    Such a design is actually nothing new in terms of actual technology, it's just a good portable antenna design choice based on the basic fundamentals of solid antenna theory.

    When you unroll the wire from the reel, it changes resonance in terms of it's operating frequency. Coverage is from 40 thru 6 meters.

    Now you can leave the tuner at home. The tuner is now built into the antenna instead! :)


    How? Notice the paint marking on the wire above...

    When completed, the paint markings on the wire represent the band of operation.

    For example, to "tune" the antenna from 20m to 17m all you need to do is calculate the differences in terms of wire length / frequency relationship required between the next two bands in order to find how much wire needs to be reeled up inside. (subtracted amount.)

    For 40 meter operation, you simply unroll all the wire from the entire reel. (no paint marks required)

    30 meters = 1 paint mark on each side of the dipole
    20 m = #2 paint mark
    17m = #3 paint mark
    15m = #4 paint mark

    etc etc..

    To calculate required wire dimensions:

    If one leg of a dipole cut for 20m CW portion of the band is:

    16' 7" long and if

    One leg of a dipole for 17m CW portion of the band is

    12' 11" long

    And if the antenna has a good VSWR reading on the previous band, then collapse the wire inside the reel exactly 4' 2" and that will be the difference between operating on 20m to 17 meters.

    Once you have done that, check the VSWR again, (tweak the wire length and inch in or out of the reel if necessary and now mark that spot on the antenna wire using the paint marker.

    Lather, rinse, repeat. :)

    Do the same thing above but for changing bands from 17 to 15 meters.

    Next you adjust and mark the wire going from 15 to 12m

    12 to 10m and so on...

    Complete the calculations and wire marking procedure on every band until you have markings on your roll up antenna wire for every band from 40m though 6 meters.

    4 reels are used.

    2 of the reels are intended for the wire.

    2 of the reels are intended for dacron rope.

    These are camping clothesline reels and they cost $2 each and are lightweight.
    Replace the laundry line inside with dacron rope and wire instead.

    Just unscrew the two halves of the reel to accomplish this.


    The "outer" reels contain dacron rope are they are intended to anchor the antenna and keeps the ends of the antenna elevated off the ground. This helps to improve efficiency.


    Note the flexweave wire (antenna) is on one side and Dacron rope (anchor) is on the other side. This rope leads to the second reel installed at the ground below.


    To the feed point photo perspective... (Feedpoint can be hung from a tree branch or attached to a telescopic pole as shown.)


    Feedpoint constructed from simple pvc cap, eye screws and SO-239 connector:


    How to construct:

    1. Drill a hole and install SO 239 connector.

    2. Drill two holes on each opposite side of the PVC cap and install eyescrew with one nut - 2 washers - and one wingnut on the "outside" of the PVC cap side.

    3. On the inside of the PVC cap, install two washers and one nut.

    4. Connect two short wires of equal length from the SO-239 connector between the two washers on the inside of the PVC and secure BOTH nuts together. (The nut on the "inside" of the cap is tightened and pressing against the nut installed on the "outside" of the cap.)

    5. Loop the antenna wire around the eyescrew before connecting between the washers and tightening the two washers together using the wingnuts. This ensures added mechanical strength and prevents the wire from becoming frayed otherwise from tension occurring directly at the "wingnut" location. No tension is placed at the wingnut / washer point because the eyescrew is now taking all the stress when the wire is wrapped on the eyescrew in this manner.


    Portable lightweight multiband antenna system for operating QRP from 40 - 6m.

    Everything fits inside this nylon zip up carry bag, including the LMR-200 feedline!

    Last edited: Dec 18, 2015
    KM4OYP, AF7TS, KU4X and 1 other person like this.
  4. W7CJD

    W7CJD Ham Member QRZ Page


    I have questions about your yo-yo DIY antenna.

    Does all that wound up wire change the calculated length much?

    Have you used it QRP?

    Is it efficient in terms of ERP - Effective Radiated Power compared to a dipole without the wire on the reels, or less ERP?
    Last edited: Dec 18, 2015
  5. KA9UCN

    KA9UCN Ham Member QRZ Page

    I have worked some qrp but after working mostly 100 wats to QRO have found that a traped dipole is a very efective antenna. It is simple to install, easly portable and requiores no tuner for the bands it is designed for. The traps act like loading coils so this makes it somewhat although not much shorter. I have worked a bit of 80 meter ssb qrp and found it to be a tough band. In this case there was not a lot of distant contacts with the trap dipole but for good contacts out to a couple hundred miles. I have found a low full wave coax fed loop worked NVIS with very surprising results.

    In the spring I plan on dedicating most if not all my ham related efforts to QRP just for the chalange and enjoyment of simpler home brew equipment.

    You can bust about any pile up QRO with a beam but the chalange is to do it with minimal equipment and power. If that does not work i can always turn on the grid driven amp and go back to QRO.
    I do like the above mentioned DIY yo-yo antenna.

    Joe KA9UCN
  6. W7CJD

    W7CJD Ham Member QRZ Page

    I like that he tells us how to do the DIY.

    How was that low full wave coax fed loop made?

    Last edited: Dec 19, 2015
  7. KA9UCN

    KA9UCN Ham Member QRZ Page

    The loop was of conventional design, no balin or ferrite.

    I cut a full wave + for 80 meters from no.14 stranded antenna wire. Connected the center of the coax to one end and the braid to the other end of the wire. Strung it through the trees at an average of 20 foot in a very rough hexagon shape loop then trimmed to resonance.

    Joe KA9UCN
    W8ZNX likes this.
  8. W7CJD

    W7CJD Ham Member QRZ Page

    Really. I have never had that description: center of coax to one end and the braid to the other end of the wire.

    You trimmed to resonance, resoldering directly to the coax, then?

    How much length coax?

    I am asking, because the description for loop antennas are so weak in detail.
  9. KA9UCN

    KA9UCN Ham Member QRZ Page


    The single band loop is about as easy as an antenna can be. Yes just solder one end to the center conductor of the coax and the other to the braid. I make it a bit longer than 1 wavelength and then just fold the excess back onto the wire at any convenient point in the loop to tune. Any length of coax will work. Just remember the basics of coax length and loss. The loop exhibits a bit higher feed point impedance than 50 ohms, usually around 100 so a feed point mismatch of 2 to one is common however with tuning the loop length this can usually be reduced to a very close match and will require no tuner. 50 or 75 ohm coax can be used. The loop can be used as a multi band antenna but that is a more in-depth discussion. If anyone is interested I will be happy to post more on the subject .


    Joe KA9UCN
  10. W7CJD

    W7CJD Ham Member QRZ Page

    Joe, KA9UCN

    Please start a thread right here in QRP Corner, about the simple wire loop antenna.

    I have read with interest about wire loop antennas for many years, since I saw the first delta loop and the Big Loop.

    The "little details" are missing, however.

    I think the wire loop antenna deserves it's own thread.

    It can be an efficient antenna in terms of ERP and reputedly have gain, as well.

    There are participants in the forum that can demonstrate antenna performance graphically with software.

    If you have a thread, they may show up to participate in the thread.

    I have seen willingness to do so, if a thread is about a specific antenna.

    Everyone benefits.

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