Most Efficient Antenna for QRP

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

ad: L-HROutlet
ad: l-rl
ad: Subscribe
ad: Left-3
ad: MessiPaoloni-1
ad: L-MFJ
ad: Left-2
ad: K5AB-Elect-1
  1. W7CJD

    W7CJD Ham Member QRZ Page

    Okay, here is the challenge: what is the most efficient antenna for QRP portable.

    Why? How?

    For me, a resonant doublet that has no common mode gets the signal out. This has meant getting the feedline length right. I optimize height for the frequency, 32-33'.

    What do you say?

    If you use coax, how do you determine feedline length if you use an antenna analyzer, or, do you use a balun or a 1:1 common mode balun and call it good?
     
    Last edited: Dec 15, 2015
  2. KK4NSF

    KK4NSF Ham Member QRZ Page

    that is a good question... At the moment, I'm studying and experimenting with just that issue, and haven't reached any firm conclusions yet.

    It is important when discussing "most efficient" to work with objective measurements of some sort, like SWR, Field Strength, Published Data, and so forth.... so we have an objective way to compare our results and avoid basing our future antenna set-ups on opinions that may or may not be substantiated in fact.

    One thing I'm seeing is a strong reliance on the number of QSOs as a measure of an antenna's quality. While that may be an indicator of sorts, it also may not be. A few weeks ago I made 20+ QRP QSOs in two hours using a Hamstick duct-taped to a camera tripod. While it did make good QSOs on that day, I really doubt it was a very efficient radiator.... it was just a good radio day.

    The other thing I'm curious about is the often-stated comment that Antenna Tuners cause a loss of signal strength. While it does seem to be a reasonable idea, I haven't been able to find any published data supporting it. If it DOES cause a loss.... which we as QRPers can't afford, how MUCH of a loss does it cause? A little or a lot?

    Dave
    KK4NSF
     
    Last edited: Dec 15, 2015
  3. W8ZNX

    W8ZNX Ham Member QRZ Page

    ahoy

    what band low or high, what i would use for 40 meter rag chew
    is not the same as what would use when 10 is hot and the DX is rolling in

    when, car camping or backpack hiking in camping, can you just take it out of the trunk
    and use it near the picknick table or are you going to carry it in 18 miles

    where, by the sea shore, in a forest with lots of tall trees or on a mountain top
    sea shore go for a vertical, in the woods use the trees, on mountain top
    lots of people go for metal self supporting jobs

    most efficient antenna for QRP
    is the same as the most efficient antenna for QRO

    well made and used antenna tuner causes negligible loss

    i use a tuner most all the time home and in the field

    have used most back pack camping
    end fed wire either as a bottom feed sloper, inverted L, inverted V,
    inverted U (depending on trees) with one or two wire counterpose on the ground beneath it
    to a simple tuner

    have also used a St. Louis vertical look it up it is a tried and tested
    QRP HB vertical last used it camp cruising a sailing dinghy with a tuner and IC-703

    have played with dipoles, all kinds of verticals, a few store bought lashups and a kite antenna

    the kite antenna worked great
    it can be lots more work, often the wind and place is not right for kite work
    ( was a avid kite flyer still own a few dozen big kites )

    keep going back to simple wire and tuner

    read
    book sellers need the business
    still in the stacks

    mac
     
    Last edited: Dec 15, 2015
  4. KK4NSF

    KK4NSF Ham Member QRZ Page

    are you sure we're not long-lost brothers? I've got several replica Weather Service kites that I've used to hoist up instruments and antennas. One of them even has an APRS system to relay it's altitude. Kite make great antenna supports when the wind is blowing.... until they get ~400 ft up or so. Then they get sort of static-y BbbbzzzzzzzzzAAAP
     
  5. AG6QR

    AG6QR Subscriber QRZ Page

    Antenna tuners just add inductance and/or capacitance in series and/or parallel with the antenna. An ideal inductor or capacitor can't produce any loss -- it dissipates no energy. Unfortunately, real antenna tuners are made of real inductors and real capacitors, and those things always have at least a little bit of real resistance associated with them. The amount of loss will have to do with the amount of resistance added. How much will it be? It's very hard to say, and the answer will depend on which inductors and/or capacitors are switched in the circuit for the particular antenna and band we're talking about. It may be negligible, or it may be enormous. The only thing we can say for certain is that it won't be zero.

    The losses in a tuner will be lower if the tuner doesn't have to switch in large inductance, nor high ESR capacitors. It'll be lower if the inductors are made with heavy gauge wire. It'll be lower if the inductors keep their cores well below saturation.

    If you can tune the antenna directly, by lengthening/shortening the elements, that's probably going to be more efficient than adding a tuner. That's often fairly practical for a temporary single-band operation. But a well-made tuner used well isn't necessarily going to add much loss, and it can provide greater flexibility.
     
  6. W8ZNX

    W8ZNX Ham Member QRZ Page

    ahoy

    i forgot were the weather service kites like the French military style kite
    a box shape with wings

    always need to ground the antenna
    use a big old RF choke
    from antenna to ground

    keeps the static charge from building up

    many years ago learned the hard way
    blew out the front end of a 509 Argonaut
    lucky the 509 Argo is very very easy to work on

    years ago was a member of the AKA
    nearly wore out a sewing machine making kites

    yours truly
    mac
     
  7. W8ZNX

    W8ZNX Ham Member QRZ Page

    oh

    on kites and antennas
    years and years ago
    Ozona Bob W5PY and a T (SK)
    a famed big time old buzzard AM OP
    some times used a kite antenna

    he lived outside Ozona Texas
    which is out in West nowhere by gosh Texas
    the wind would be steady for days on end

    one night all the receive signals dropped off the map
    and his transmitter went screwy

    the antenna and kite had broken loose
    dragging the antenna wire for a mile or so
    to a power sub station

    knocked out the power to Ozona Texas
    they never found out who did it
    Bob never used a kite antenna again

    dit dit
    mac
     
    KU4X likes this.
  8. W7CJD

    W7CJD Ham Member QRZ Page

    ..some antenna tuners have a bypass.

    Is there a radio amateur that doesn't know great propagation or even good or fair propagation makes a fine day for amateur radio, and has very little to do with the "best" antenna, or not.

    Least loss. Most current at the feedpoint. I have heard these things.

    I am interested in objective and quantifiable knowledge, as well. Not only loss, but gain.
     
  9. W8ZNX

    W8ZNX Ham Member QRZ Page

    ahoy
    your question is not so much a QRP question
    but a antenna question

    your question may get more reply's
    posted in the antenna forum

    dit dit
    mac
     
  10. W7CJD

    W7CJD Ham Member QRZ Page

    Been there, done that. I was told to read a book.

    I think no one had an answer.

    However, QRP levels output makes the point doesn't it.

    I want to see straightforward answers online, anyone can get with an online search, rather than purchase books, CD's, DVD's and website memberships at the antenna websites like Cebik or antennaX.
     
    W4SEX likes this.

Share This Page