DB 212 antenna info

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WB0EMJ, Nov 8, 2017.

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  1. WB0EMJ

    WB0EMJ Ham Member QRZ Page

    need distance between tower and element when mounted, need measurement between folded element it's self not the distance between the elements. I would also like the details on the feed connections it some one has them. I want to build 4 of these elements out of copper tubing for my 6 m repeater.
     
  2. K8JD

    K8JD Ham Member QRZ Page

    That's a lot of copper !
     
  3. W9GB

    W9GB Ham Member QRZ Page

    13F1A10B-DE75-4CBB-838D-13B4BAF0684D.jpeg
    Decibel Products (Allen Telecom) DB-212 Series
    25-50 MHz Side Mount Gain Antennas
    Assembly and Mounting Instructions
    http://www.repeater-builder.com/ant...sembly-and-mounting-instructions-(andrew).pdf

    Andrew Corporation DB-212
    Exposed Dipole Quasi-Omni Antenna
    28-88MHz / Up to 12.2 dBd Gain
    http://www.repeater-builder.com/antenna/db/pdfs/db-212-catalog-sheet-(andrew).pdf

    Modifying the DB-212 Antenna
    by Joel Huntley, WA1ZYX and John Haserick, W1GPO
    http://www.ccdx.org/zedyx/mods/db212.htm
    ==
    The DB-212 is based on the DB-201 omni-directional antenna.
    My father had a DB-201 installated for 45 years on 46 MHz, tough antenna.
    Chuck Adams, N5UN covers that antenna and its evolution, to DB-212.
    http://www.xanaduu.com/db201/

    Sinclair Technologies (Norsat)
    Model SD-212D
    http://www.sinclairtechnologies.com/catalog/resources/pdf/SD212D-SF2P2SNM(D00)-DI.pdf
     
    Last edited: Nov 8, 2017
  4. WB0EMJ

    WB0EMJ Ham Member QRZ Page

    looked at all of these sites none have the info I need
     
  5. WB0EMJ

    WB0EMJ Ham Member QRZ Page

    lot cheaper than the $1600 they want for one of these I can build the phasing a harness and elements for under $100
     
  6. W9GB

    W9GB Ham Member QRZ Page

    In other words, you don’t have original Andrew/dB mounting bracket.

    The “distance” between the mounting mast OR tower — 1/4-wavelength often used.
    For example, Cushcraft used 12 inches for their VHF/2-meter AFM series 4-bay dipoles.
    Mounted on same side of tower creates a Cardioid pattern (with shadow on backside).

    http://www.cushcraftamateur.com/pdffiles/951282.pdf

    Between folded dipoles, one-wavelength. At 6-meters that’s considerable distance.
    You could go closer, but again this influences the overall radiation pattern.
    You can model (NEC-2) closer spacing to the tower/mast and its influences on radiation pattern, especially if you desire omni-directional — or something else.

    KH6AQ modeled a WB9WIS 6-meter antenna using NEC-2 in 2010 (eHam.net).
    http://www.eham.net/ehamforum/smf/index.php?topic=69022.0


    Numerical Electromagnics Code (NEC) simulates the electromagnetic response of antennas and metal structures. Developed in 1981, under contract for U.S. Navy, NEC2 was later released to the public and available on most computing platforms.
    http://www.nec2.org/

    U.S. Patent, # 3299429 (filed August 5, 1963).
    Inventor: Thomas McMullian, Decibel Products
    https://www.google.com/patents/US3299429
     
    Last edited: Nov 8, 2017
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Dimensions for each dipole: See attached.

    Spacing from feedpoint to feedpoint of each dipole: 227"

    Coaxial phasing/matching harness: 35.6" of RG-11A/U (75 Ohms) connected at feedpoint of each dipole, then connected to 112.4" of RG-213/U (50 Ohm solid PE dielectric) coax at each antenna, brought to a coaxial "T" adapter midway between the two dipoles.

    This is for a 2-dipole array. For a 4-dipole array, each pair (upper 2 and lower 2) should be configured exactly as indicated then combined using a third coaxial combiner made of two lengths of only 50 Ohm solid PE dielectric cable like RG-213/U, 187" long each, brought to a third coaxial "T" adapter to form the transmission line connection.

    I wouldn't use copper except as a truly last resort: Weight-to-strength ratio is lousy compared with common aluminum alloys normally used to make these antennas. To bend the aluminum tubing for each end of a folded dipole, I use tubing a few inches longer than required, flatten one end to pinch it off, and fill the tubing with sand before bending around a form. After it's bent, pour out the sand and check all final dimensions.

    For a repeater site, I'd mask the open "ends" of each tubing section (two places on each folded dipole) and have each dipole anodized, painted or powder coated before final assembly on the tower.
     

    Attached Files:

  8. W9GB

    W9GB Ham Member QRZ Page

    That distance is: 5.766 meters (~1 wavelength).

    eHam.net discussion on bending tubing for Folded Dipole (2012).
    http://www.eham.net/ehamforum/smf/index.php?topic=85850.0

    Justin, G0KSC popularized the usage of Stauff hydraulic tubing clamps
    http://www.stauffusa.com/customer/stcorp/catalog/clamps.htm
    and pipe benders for DIY building his Yagi and LFA designs.
    http://www.g0ksc.co.uk/shop.html
    In the USA, these items can be found at McMaster-Carr or Stauff distributors.

    LFA Loop, G0KSC sells a nice pipe bender for 3/8” aluminum tube (LFA and OWL Loop bends)
    G0KSC Pipe Bender
    http://www.g0ksc.co.uk/shop/pipe-benders/pipe-bender-lfa-loop-G0KSC_Antenna_parts.html
    Zoro Tools (W.W. Grainger’s Internet business) sells an equivalent tool.
    https://www.zoro.com/airsept-tube-b...9_YA7_Vued82mbAcktpcwyke3Ov5f-f4aAs03EALw_wcB

    That method (fill tubing with sand before bending) was also common for truck/automotive fuel line bending. One mistake I saw in 1970s (adding 2nd fuel tank and selection valve to truck) during oil embargoes — auto tech forgot to empty the sand (formed a solid plug).
    Fortunately, no engine damage.
     
    Last edited: Nov 9, 2017
  9. WB0EMJ

    WB0EMJ Ham Member QRZ Page

     
  10. K7JEM

    K7JEM Ham Member QRZ Page

    I built a copper dipole like this for 2M, modeled after a single element on a DB224. The element needs to be spaced off the tower about .03 wavelength, or for six meters that would be around 6". This close spacing to the tower reduces the feed point impedance to around 100 ohms, so it is critical. Once it equals 100 ohms, it is easy to match to 50 ohms by using a QW section of 75 ohm cable.

    The easiest way to find the spacing is to build your element, attach a QW length of 75 ohm cable, then adjust spacing for best 50 ohm match. It will be somewhere around 6", depending on the specifics of how the element is constructed.

    You will probably need standoff insulated spacers for the upper and lower segments of each element, as well as a center insulated standoff at the feedpoint.
     

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