GAP Vertical vs. New Carolina Windom performance

Discussion in 'General Technical Questions and Answers' started by KJ4DNW, Sep 8, 2008.

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  1. KJ4DNW

    KJ4DNW Ham Member QRZ Page

    This weekend I had a chance to install GAP Eagle DX into it's permanent location. It's installed at top of 23 feet "tower" (chimney) and has a clear sky view (using 50 feet of LMR240 to TS-2000).

    SWR are more or less as advertised on all bands (tooks a bit tweaking/tuning to get there).

    I have compared Eagle performance with my home brewed New Carolina Windom installed about at 20 feet inside attic.

    I have tested long and short skips (like Madrid Spain, Canary island and Caribbeans, Mexico)

    The results were kind of not what I would expect.

    On 20 meters, 90% of the time Windom had on 1-2 S units better signal.
    10% of a time Eagle was on par with Windom.

    On 10 meters, Eagle was 2 S units ahead of Windom (listening K4AIS beacon, very close to my QTH)... well this is might be encouraging but band is dead for now. (Or may be my home brewed Windom does not work at all on 10 meters)

    Eagle was a bit less noisy - well, may be because signal level was down against Windom and location was further away from house power lines.

    Speaking about low angle of radiation for verticals:
    Aruba gave me 58 on Windom and 57 on Eagle - so it's about the same.

    I was thinking that Eagle would have a better transmitting performance for DX station because of lower take off angle but it does not look to be happened.

    Well, it was a pretty much educational experience (I'm trying to justify for myself amount of money spent on commercial antenna :) ).

    The postulate "Size does matter" stays true (Windom is 66 feet of wire and Eagle is 21 feet of aluminum tubing).

    The other postulate is - "eham's reviews needs to be filtrated thoroughly".
  2. K1VSK

    K1VSK Ham Member QRZ Page

    You might consider that polarization can significantly effect what you perceive their relative performance to indicate. With respect to angle of radiation, nothing you mention would indicate actual angle - the relatively short skip to europe or the Carib from your qth isn't low angle at all and the closer stations might just as easily have been ground wave so there too your conclusions may be simple perception.

    The conventional wisdom is that the real advantage of verticals with a proper counterpoise (which you don't have) would be more pronounced on the low bands where relative performance tests such as you describe may be more precise. Unfortunately, without better ways to measure actual radiation efficiency at various angles and directions, it is impossible to come to any real conclusion which is better.

    The best advice I could offer is to A-B switch between them and make any decision which to use predicated upon which is apparently "hearing" better for the specific station with whom you hope to qso.
  3. G3TXQ

    G3TXQ Ham Member QRZ Page

    Looks like you're not alone:

    "The Gap Eagle DX produced disappointing results. By Saturday afternoon the baseball players had all gone home. So we erected a Carolina Windom from the trailer tower to the backstop. It worked much better." Day - 2006.html

  4. W5DXP

    W5DXP Ham Member QRZ Page

    Here's a very old postulate: "Verticals radiate equally poorly in all directions." Here's a comparison of my horizontal antenna and my vertical antenna on 40m.

    Broadside to the dipole, at an elevation angle of 30 degrees, the dipole beats the vertical by about 7 dB, more than an S-unit. At 45 degrees, the dipole beats the vertical by almost 20 dB. At less than 10 degrees, the vertical beats the dipole by a negligible amount.

    Off the ends of the dipole, at an elevation angle of 30 degrees, the vertical beats the dipole by about 12 dB, about 2 S-units. At 20 degrees, the vertical beats the dipole by about 22 dB.

    So which one is the best antenna??? Comparing horizontal antennas to vertical antennas is a lot like comparing apples to oranges.
  5. G3TXQ

    G3TXQ Ham Member QRZ Page

    Cecil: if folk would do as you have done and generate the azimuth and elevation data for each antenna, at least they could check it against directions and distances of interest and make an informed decision about whether the apple is better than the orange ;)

    I did some recent work on correlating elevation plots with the ARRL's "angle of arrival probabilities" for a particular path in order to arrive at a single "figure of merit" for the antenna on that path. I used it to compare antenna performance at different heights, but it could just as well be used to compare different antennas:

  6. KJ4DNW

    KJ4DNW Ham Member QRZ Page

    Cecil, thanks for my new but old postulate and for URL with antenna models.

    I did some modeling (for the best of my ability) using MMANA-GAL software.
    New Carolina Windom has some whimsical pattern on 20m, 20 feet above ground. It looks like hedgehog cloud warmer. And attic installation does not make pattern any cleaner (I don't know how to model it). I have stucco walls (inside there is a metal mesh)... does that bring ground any closer to antenna?

    So I thought that vertical dipole (by the way, GAP Eagle is set of vertical dipoles) would give some low take-off angle more suitable for for DX hops.

    Windom is positioned from SE to NW ( cannot do much about it). With all above said, I thought that GAP will get me at least Europe or Africa...
    Well, with solar flux around 67 this is not happening too often... :)

    I'm just curious how other guys doing these days getting contacts with Japan and Asia... What am I doing wrong? Do the 4 element beam with legal limit power amp make all that difference?
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    Frankly, the propagation has not been that good lately, at least most of the time, for you to get a really good idea as to just how well your antennas are going to perform. Now I have a better than average antenna installation and at the present time there are a lot of times that it seems that I cannot get out of my back yard! Go to

    for some photos.

    I looked at the Gap Eagle specifications, etc., and it is a compromise antenna. Basically, you can get a pretty low SWR on a good bandwidth when the counterpoise is not that great and the counterpoise on this antenna is not that great! I wonder what would happen if you added some "decent" radials to the antenna. That is 3 or 4 resonant radials for each band or, at least, quarter-wave radials for 40 meters and 20 meters. If you do decide to add some radials use the formula 246/F where F is in MHz and the answer will be given in feet. This is opposed to the formula for a quarter-wave antenna which is 234/F. The 234 formula takes into consideration the "end effect" of a wire that is between 10 gauge and 16 gauge. Basically, you want the radial to be the full length of a quarter-wave and that is given by the 246 formula.

    I am quite familiar with the Conyers, Georgia, area. My wife's middle sister lived in Conyers for almost 4 decades before moving to Covington several years ago. When I lived in Forest Park (my senior year at Georgia Tech) in a house that was next door to the highest point in Clayton County I only had wire antennas for HF. Now the location was virtually "perfect" for VHF with yagis like 30 feet above ground with which I could work all over Georgia and well into Alabama, Tennessee, and South Carolina. But, the wire antennas were not that high so I definitely was not a "DX big gun"!

    Now it has been my experience with vertical antennas (all of mine are full sized with elevated radials) is that for stations beyond around 1000 miles that they work great. For stations out to around 700 miles my fairly low wire antennas work great. But, for stations between 700 miles and 1000 miles sometimes one antenna works best and then the next time the other antenna works best. Of course for the bands that I have yagi antennas generally the yagis outperform a vertical by a wide margin. By the way, I live 1/2 block from the highest point in Richardson, Texas, and the ground conductivity is in the highest rated in the contiguous 48 states. That definitely helps!

    Glen, K9STH
  8. KJ4DNW

    KJ4DNW Ham Member QRZ Page

    Hi Glen,

    Yup, I saw your "antenna paradise" some times ago, when I did research about something.
    Very impressive. (You would need make an owl to land on different part of your top yagi somehow :) )

    When I did research about verticals I have read all I can find about GAP technology, GAP patent, various analyzes and reviews. I was looking for something without needs for radials cause some covenant restrictions (I'm living on a golf-course and flying RC helicopters... it's already enough :) so I would not even dream about tower with full size multi-band yagi). And my home brewed Windom hidden in attic did not look very promising.

    GAP technology is basically set of asymmetrical dipoles, you can check schematic diagrams here (fig.4 and fig.5):

    I really don't know where radials should go in this antenna.

    Thanks for giving me head ups on situation with propagation. (so even big guns have troubles going out these days) As you probably figured out I have not known better days of propagation, so I cannot compare yet.

    Hopefully, with solar cycle 24 in couple years, I can say that I can do it.

    Putting title GAP vs. Windom I don't mean to start "holy war" or diminish one vs. another. I just want to share my observations and ask if there are ways to improve my antennas.

    Thanks y'all again for information.

    Vlad, KJ4DNW
    Last edited: Sep 9, 2008
  9. WA7OET

    WA7OET Moderator QRZ Page

    Isnt the GAP a half wave center fed vertical dipole? If so then having it at 23 feet will raise the angle of radiation and will radiate a larger portion of your signal straight up. Put it on the ground and it will probably work better. If you want a vertical at 23 feet, go with a quarter wave with a ground plane.
  10. W5DXP

    W5DXP Ham Member QRZ Page

    EZNEC seems to disagree. Here are the EZNEC results for a 20m vertical dipole with the lower tip elevated by x feet.

    x', gain @ elevation angle

    1', 0.13 dBi @ 19 deg
    10', 0.79 dBi @ 15 deg
    20', 0.90 dBi @ 13 deg
    30', 1.04 dBi @ 12 deg, also 1.67 dBi @ 41 deg TOA
    40', 1.50 dBi @ 10 deg, also 2.54 dBi @ 34 deg TOA
    50', 2.18 dBi @ 10 deg, also 2.93 dBi @ 29 deg TOA
    60', 2.66 dBi @ 10 deg, also 2.93 dBi @ 25 deg TOA

    Just as for a horizontal dipole, it appears to be "the higher, the better". His 20m dipole up at 20 feet, has 7 times the gain and a 6 degree lower elevation angle than it does at ground level.
    Last edited: Sep 9, 2008
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