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Most Efficient Antenna for QRP

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

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  1. AG6QR

    AG6QR Subscriber QRZ Page

    Here's an example: A 40m monoband Yagi, three elements, on an 80' tower, clear of all obstacles, with a rotor. Better yet, a couple of properly-phased, stacked Yagis, up a bit higher.

    That's the most effective QRP I've heard of anyone using. I posted elsewhere about my club's Field Day station putting up a 40m beam on a large tower, and how well that worked with a half-watt Rockmite the night before Field Day (but for the actual FD event, they switched to a QRO radio).

    The problem with such a strategy is that, though it works well with low power, it doesn't integrate well with the spirit of QRP. That is, it's not small, lightweight, nor inexpensive. It's not portable, unless you purchase a trailer for it and consider "towable with a full-sized pickup truck" to be the equivalent of "portable".

    If you take cost and portability into account, you must compromise on performance, and the "best" answer depends on how you define your constraints, and what you want to optimize for.

    Full-sized resonant wire dipoles are a common good strategy, but you've got to support them somehow. Trees might work, but they're often too low for the lower bands, and they're not available at every operating position you might want to go to. Portable masts are always a compromise between height, strength, ease of setup, bulkiness of transport, and cost.

    If you're interested in some of the strategies and compromises of portable QRP antennas, a very good read is NE1RD's "Buddipole in the field"

    http://lib.store.yahoo.net/lib/buddipole/BIF2.pdf
    http://www.bsandersen.com/Rsc/Rsc/buddipoleInTheField.html

    That goes through some of the strategies that can be used for constructing portable antennas with the Buddipole system. And it reinforces a point I've made several times, that the Buddipole isn't an antenna, it's an "antenna construction kit", which allows the construction of a whole lot of different styles of antennas, of which some work well, and others don't. But the point which that book makes relevant to this thread is that there is no "best" answer. Even if you limit yourself only to the Buddipole system, that book took a bit more than 150 pages to describe the "best" configurations for various circumstances. If you add in the huge number of good alternatives that don't involve anything like a Buddipole type system, (wire EFHW, wire dipoles using trees for supports, magnetic loops, etc.) it soon gets even more involved.

    After all that, I say a basic standard starting point for comparison would be a full-sized horizontal dipole, tuned for the band you're using, a quarter wavelength on each side, half wavelength in total, fed at the center, up at least a half wavelength in clear air.
     
    KU4X likes this.
  2. AA9SD

    AA9SD Ham Member QRZ Page

    The best QRP antenna is a monoband yagi on a tower at 100 feet. There, that should answer the question. :D
     
    W8ZNX likes this.
  3. W7CJD

    W7CJD Ham Member QRZ Page

    I don't know what the problem is here at QRZ.com

    I was not asking for myself.

    I started the thread for the benefit of those who do QRP portable, at the QRP Corner.

    The internet is easily searchable for helpful information.

    Since you apparently have no interest in QRP, QRP portable, or, an efficient antenna for QRP, and seem determined to ridicule, why don't you stay off a thread strictly for QRP.

    My next post will be to report a complaint, if you insist on litering this thread with ridicule.
     
  4. AF7TS

    AF7TS Ham Member QRZ Page

    I am a new operator interested in this thread. I am very good with math, and my head is full of theory...but I would really appreciate examples of _practice_!

    If I may be so bold: I think that the original poster in this thread had a very good idea, but (as with anything on the internet) needed to clarify the question. I am going to rephrase what I think the question is, and what _I_ am interested in:

    For portable, HF, QRP operations, what antenna has worked best _for you_? What compromises did you make while still achieving an efficient system?

    I am not asking for theory about what is 'best', since that is written in lots of books; I am asking for you to share your real world experience with the rest of the world.

    Many thanks!

    73
    Jon
    AF7TS
     
    W7CJD likes this.
  5. W7CJD

    W7CJD Ham Member QRZ Page

    Thank you.

    If you can demonstrate that you used an antenna analyzer or modelling software, please explain what you did.

    This particular thread is about efficient attennas for portable QRP.

    The problems of metal buildings, power lines, your own and your neighbors RFI problems are not of interest, not in this portable QRP thread.
     
  6. AI6KX

    AI6KX Ham Member QRZ Page

    Sometimes I chase DX with QRP at home when the bands are hot, and sometimes I take the QRP gear out to some nice location to get away from the local noise. At home my main antenna for 20, 17, 15, and 10 is a vertical groundplane that has sets of parallel tuned elements, both the vertical radiator and the 4 radials. It works great after having done the expected tuning (trimming), and a good part of the reason is that the base is about 40 feet AGL. I also have a 15-meter Moxon that worked right off the bat and did not require tuning, perhaps because it is on a PVC mast and boom.

    I was referring above to a lightweight three-band parallel dipole I made for portable use on 20, 17, and 15 meters. It is no different electrically from any other coax-fed parallel dipole, and I tuned it just the same way most folks do, by cutting the wires a little longer than calculated and then folding them back around the end insulators for lowest SWR in the CW parts of the bands. I find that the height of the feedpoint or the ends makes very little difference to resonance although it obviously affects how well I can work out. I use a 45-foot length of RG-174 to feed it but I carry an extension if I am at a location where I can hang it higher. A few fishing swivels make it easy to fix if the wires get twisted on the way up. And no tuner is needed since the SWR is low. I tried a choke balun using a FT140-43 toroid but found it was not necessary and just weighed down the center. Here's a pic of the antenna wound on a 12"x12" lightweight rubber floor tile that also makes a nice insulating seat cushion. antenna.jpg The wire spacers are made from plastic clip material that I found does not degrade in sunlight and grips the wires a little. I leave about 20 feet of the green cord tied permanently to the ends and don't bother with insulators.

    I am also trying various single-wire/counterpoise combinations in the event I can't hang the dipole from two supports. For that I have modified a cheap "eBay antenna tuner" kit to work better on 20, 17, and 15. I can "tune" to get minimum SWR but don't think that always gives maximum radiated power so need to make a little field-strength meter to finish my QRP kit.

    73 and happy QRP holidays to all,

    Steve JS6TMW in Okinawa
     
    Last edited: Dec 17, 2015
    W7CJD likes this.
  7. WB3BEL

    WB3BEL Ham Member QRZ Page

    There are lots of efficient antennas. The fact that you use them when running low power does not make them more or less efficient.

    There are antennas that are efficient that are not very effective.
    As any antenna engineer knows, all it takes to make an antenna efficient is that it radiates most of the energy applied to it.
    There is no requirement that this radiation goes in any specific direction.
    You could have an antenna that radiates down into the ground and is very efficient but is a terrible antenna from a practical perspective.

    While I prefer to use efficient antennas, that is not my foremost requirement when considering antennas for construction.

    I think it makes more sense to consider criteria (in no specific order) like:
    Size, Weight, Cost, Gain, Pattern, Match, Mechanical Reliability, Aesthetics, Frequency Range, Return Loss, Impact of water or ice...

    I am sure that some smart amateurs can think of dozens more and stop using the word efficient when they are thinking about "good" antennas and have stopped to think what they want in a "good" antenna for a specific application. I am pretty sure there is no best antenna for all applications, but don't know if I can come up with a formal proof.

    If you think that you are getting vague answers, you are probably asking vague questions to people of various backgrounds and abilities. Most of the answers will be sort of right or sort of wrong. If you can't tell which is which, you are left to chance. Such is the nature of internet forums. Books on the other hand have often been reviewed. If they are good then they get revered. If they are full of mistakes, people notice and they eventually end up in the junk pile. There are exceptions as well, there are some pretty poor books that people think are good even on the subject of antennas. It is nice that the internet has lots of free information on all kinds of subjects that is nothing short of amazing. But you have to have some guide to tell you what is good and what is bad.

    You need to start with some fundamental knowledge and use it as a ruler to measure the truth or falsity of other information before you trust it.

    Here are some basic antennas I think are pretty good for many applications. They also appear in many antenna books and even on the internet.

    1. Basic monoband half wave dipole (everyone who is a radio hobbyist should be familiar with this)
    2. Ground plane quarter wave vertical with radials or ground system
    3. Monoband Yagi
    4. Loop antenna

    Here are a few antennas that I think are junk and the ARRL should stop promoting or publishing projects about:

    1. J-Pole antennas (The Ground plane quarter wave is better in every regard)
    2. Antennas that rely on feedline radiation to work like TakTenna and similar

    Here are a few antennas that I don't like and never use anymore because I think there are better alternatives for my applications but I can see some value in limited cases:

    1. Offset feed antennas
    2. Quarter Wave Verticals with no or limited ground systems.

    These are just some examples, I am sure that lots of folks can think of a whole lot more to add to each category. But here is the kicker... You will find that one persons anathema is another persons favorite. Is physics different for different people?
     
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  8. W7CJD

    W7CJD Ham Member QRZ Page

    WB3BEL,
    "As any antenna engineer knows, all it takes to make an antenna efficient is that it radiates most of the energy applied to it."

    It is nevertheless, imperative for QRP.

    ..and please refrain from insulting those who choose QRP.

    Frankly, this is not Beginners Corner, this is QRP Corner.

    Nevertheless, it would be helpful to get "Why" and "How" efficient explained about the efficient QRP antenna a respondent's to this thread choose to write about.

    I did not start a thread about one antenna.

    I do have the impression some antenna designs (or, types) will never be efficient.

    On the other hand, I have the impression those antenna designs (or, types) can be made more efficient.

    Think how helpful "Why" and "How" would be, in contrast to all the "opinions" about this or that antenna on the internet.

    There might be another thread about "best" for QRP portable.

    This thread isn't about "best" for QRP portable.

    That thread is about an efficient antenna for QRP portable: How. Why.

    What do you know about that?
     
    Last edited: Dec 17, 2015
  9. WB3BEL

    WB3BEL Ham Member QRZ Page

    Yes I have made tens of thousands of QRP contacts including over 300 DXCC entities. I understand quite a bit about QRP.

    I don't mean to insult anyone and am sorry if you took it that way. I still feel there is a lot of valuable knowledge in my previous post that many people reading the thread may benefit from. If you already know this information that is fine too.

    Hope you enjoy your radio experimentation and all kinds of operation.

    73, Harry WB3BEL
     
    KU4X likes this.
  10. W7CJD

    W7CJD Ham Member QRZ Page

    I agree it is beneficial.

    Thank you, for posting to the thread.
     

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