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40/80/160 Trap dipole

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB2E, Apr 13, 2018.

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  1. KB2E

    KB2E XML Subscriber QRZ Page

    I was wondering if anyone has any experience with trap dipoles? I found an old design for a 40/80/160 trap dipole and was thinking of ditching my Windom. I'm not terribly pleased with it and the dipole is about the same length and will give me 160 although not ideal I'd have it at least. Just a thought. Any opinions would be helpful.
  2. N2EY

    N2EY Premium Subscriber QRZ Page

    What is the exact design?

    How high can you put it?
    K7TRF likes this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Knowing the exact design would certainly help, but in terms of general behaviors a trap dipole is a full length dipole on the highest frequency band (40m) and should behave similarly to a monoband dipole installed at the same height. As you move to lower frequency bands you have additional loading and overall antenna shortening on each of the lower frequency bands.

    The big impact of that shortening and loading is reduced SWR bandwidth on those lower frequency bands. IOW, the 80m SWR bandwidth of a 40m/80m trapped dipole will be reduced relative to a full sized 80m dipole. Similarly and to a greater extent the SWR bandwidth of a 40m/80m/160m trapped dipole on 160m will be less than a monoband 160m dipole.

    Traps also introduce a bit of loss, but that can be minimized with good trap design. The reduced SWR bandwidth on the lower frequency bands is usually the bigger limitation.
  4. KB2E

    KB2E XML Subscriber QRZ Page

    It's 124 feet long with a 7 Mhz trap at 32.2 feet, 11 feet down from that is a 3.8 Mhz trap and then there's 18.3 feet of wire after that. I can put it up about 30-35 feet max. I want to try something else because I'm not too pleased with my Windom. I thought about a fan dipole but I have a 6BTV that "sings". Not really great on 40, good on a small segment of 80 and great on 10/15/20/30/60 (add-on kit) and 17 (my own add-on). I ran across this design and thought I could build it for another section of 80 and 40 and I'd have 160 as a bonus. I know that 160 is tough and this antenna may not be the best but it's what I can do in my lot. I'm also considering an end fed starting off the verticals mounting post and using the same radial field. I know there'd be some interaction between the two antennas but in my experience it is minimal. I once had an end fed going by the vertical missing it by only 2 feet. I did have to do some minor adjustments to 80 and 40 on the vertical but all seemed to work well. It would be worth trying. It's fun to experiment. However it would be much easier to just use the ropes I already have in place holding the Windom and just hoist a new dipole up. If I did the end fed I'd probably leave the Windom up and play with length to see if I can get dialed in a little better.
  5. KI8DJ

    KI8DJ Ham Member QRZ Page

    Check out Hypower Antennas they have such an antenna with loading coils that act as traps. They are extremely well made and very reasonably priced. And no I am not affiliated with the company.
    KU3X likes this.
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The only problem with those dimensions is those are high-L, low-C traps and greatly shorten the antenna, which leads to very limited operating bandwidth. I'd expect maybe 20 kHz BW on 160m, and probably 40-50 kHz on 80m. Mismatch departing much beyond that can become so high that they don't even receive well.

    However, having said that, I do use a trap dipole which is also shortened by loading coils on 160m and it's tuned to the bottom end of the band (resonates about 1.820 MHz), which I favor since on 160m I'm about 99% CW. Mine is up 55' at the apex (inverted vee) with the ends at about 20' above ground and it's far from ideal but does make contacts. Focusing on working "the big guns" who have superior stations, I've worked EU, JA, all the Caribbean and South America, plus about 45 states from here in southern CA. But if the other station is equipped like mine, that doesn't happen.:p

    When it "does" happen is during major contests when the big guns are on.
  7. N2EY

    N2EY Premium Subscriber QRZ Page

    Is this design online anywhere? Or, was it in QST?

    How are the traps made?

    73 de Jim, N2EY
  8. W9GB

    W9GB Ham Member QRZ Page

    Build a Space-Efficient Dipole Antenna for 40, 80, and 160 meters
    QST magazine
    July 1992, pages 35-36
    by A.C. Buxton, W8NX
    Uses RG-58/U and PVC for trap construction.
    The 40/80/160 Meter Coil-loaded Inverted V Dipole Antenna
    by Paul, KG0ZZ (Bonner Springs, KS)
    160-80-40 Metre Trapped Inverted-V Antenna (June 2017)
    by VK4ADC (Austraila)
    W3DZZ antenna for 40 and 80 meter band (November 2010)
    by Palle, OZ6YM (Denmark)
    Adding 160 meter traps (February 2011)
    Last edited: Apr 14, 2018
  9. W9GB

    W9GB Ham Member QRZ Page

    History of Inductor-Capacitor (L-C) Trap Antennas

    H. K. Morgan published Multifrequency Tuned Antenna System in the magazine
    Electronics, vol. 13, August 1940, pp. 42-50.
    This was the introduction (and publication) of L-C (inductor-capacitor) trap antennas
    from his US Patent submission (1937) and Approval (1938).

    After World War II, with the expiration of the Morgan patent,
    Chester L. Buchanan, W3DZZ (sk, 2010) wrote a series of articles on trap antennas
    (80/40 wire and tri-band beam: 20-15-10) in the March 1955 issue of QST magazine (page 23).

    W3DZZ designed several trap dipoles; trap beams; and individual L-C traps that were sold by the Fredrick Tool & Engineering Corporation. One prominent reseller of W3DZZ traps was Harvey Radio in New York. In the late 1950s, with best sunspot maximum of the 20th century, a number of companies introduced horizontal beam and 1/4-wave vertical antennas using L-C traps.
    Hy-Gain (AVQ-series) and Hustler (BTV-series) trap 1/4-wave verticals
    Hy-Gain and Mosley designed tri-band (20, 15, 10m) horizontal trap dipole antennas.

    The original W3DZZ article, The Multimatch Antenna System, on his trap design appeared in the March 1955 issue of QST magazine, page 23.

    Characteristics of W3DZZ traps:

    L = 8.2 uH (solid 14 AWG wire)
    C = 60 pF (coaxial style capacitor)
    6 inches in length
    6 ounces in weight
    Q over 100

    The dipole contains one trap on each segment at a distance of 9.75m (32 ft) from center insulator. Traps are made of a parallel circuit constituted of a coil of 8.2 mH and a capacitor of 60 pF.

    Documentation indicates that efficiency of system:
    Loss per trap ranging between 0.2 and 10.5% (0.006 to 0.5 dB) depending on the frequency, the lowest the highest loss.

    Practical Wireless magazine article
    by Len Paget, GM0ONX on construction of W3DZZ trapped dipole trap dipole.pdf

    Fred Reynolds, W2VS (sk) developed the Unadilla trap during this same time period.
    Coaxial capacitor (C) and wire coil on a black or blue plastic form (L).

    Unadilla W2VS traps developed by Fred Reynolds.

    Ralph Jannini is the engineer at Unadilla.

    Al Buxton, W8NX wrote construction articles in QST and
    ARRL Handbook/Antenna Handbook for coaxial traps, since the early 1990s.

    Rebuilding Yagi Traps by VE1ZA
    The Good, the Bad, and the Ugly (Halifax weather and traps)
    Last edited: Apr 14, 2018
  10. K2XT

    K2XT Subscriber QRZ Page

    I have no experience with trapped dipoles, but considering what was said about the limited bandwidth I wonder how the traps hold up when/if the antenna is used a bit off resonance, especially if an amp is used.
    In my case, I run a plain old inverted vee on 75 meter ssb but it is resonant down around 3550. The swr is around 4:1 and my tube type amp handles it. But if it was trapped how would the traps take the power?

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