lpda1.art

一个很小和天线计算程序

06 June 1991

FROM: Wayne M. Sarosi
      AFA2GN, PAFB MARS Team, Patrick Air Force Base, FL

To:   All MARS operators.

SUBJECT: Log Periodic Dipole Array (LPDA) Design

DISCUSSION:

This antenna was designed to operate from 13.8 MHz to 28.8 MHz. The antenna
was to cover the majority of the USAF MARS frequencies yet give the operator
a smaller log periodic than the commercial types, that had reasonable gain,
and was cost effective to build. All design formulas are taken from the
ARRL Antenna Manual. 

The antenna did not turn out as planned. The frequency range actually went
from 13.5 MHz to 29.5 MHz with SWR less than 1.8:1. Most SWR readings were
less than 1.5:1 across the band. The weight was a surprize also. I expected
100 pounds plus, but actually was under 63 pounds. 


SPECIFICATIONS:

     Boom: 22-ft, 3-in diameter, aluminum. 
     Number of Elements: 10
     Feed: Balanced
     BALUN: 4:1
     Weight: 62-lb
     Windload: near 9 sq.ft.
     Cost: About $200.00  Note: $150 for element insulators from HY-Gain.
                                $50 for misc. Tubing, boom, etc from 
                                 old antennas discarded by fellow hams,
                                 CBers, and field day.
     Time: 80-hrs, including install.
     Design Bandwidth: 13.8 MHz to 28.8 MHz
     Actual Bandwidth: 13.5 MHz to 29.5 MHz*, Highest my TS-430S would go.
     SWR MAX: 2.1:1
     SWR AVE: 1.4:1
     SWR LOW: 1.1:1, all taken on an MFJ-986 Differential-T Tuner/SWR/PWR
                     meter.
     EST GAIN: 6dB
     PWR Handling: Max Legal.
     Turning radius: same as 20m, 3 element Yagi
     Height off the ground: 35-ft minimum for best results 
                            (half wave at 14 MHz).

     ELEMENTS: (Half element lengths given and quantity)
               Note: Elements start at rear, longest first.
          
          L10: (492/13.8)/2 = 17.826-ft, quantity (2)
          L09: L10 * 0.9 =    16.043-ft, quantity (2)
          L08: L09 * 0.9 =    14.439-ft, quantity (2)
          L07: L08 * 0.9 =    12.995-ft, quantity (2)
          L06: L07 * 0.9 =    11.696-ft, quantity (2)
          L05: L06 * 0.9 =    10.526-ft, quantity (2)
          L04: L05 * 0.9 =     9.473-ft, qauntity (2)
          L03: L04 * 0.9 =     8.526-ft, quantity (2)
          L02: L03 * 0.9 =     7.673-ft, quantity (2)
          L01: L02 * 0.9 =     6.906-ft, quantity (2)

     ELEMENT SPACING: d(L10-L09) = 2*(.5(L10 - L09) cot(0.5 * apex angle))
                      The cot(0.5 * apex angle) = 2.
                      Thus: d(L10-L09) = (L10 - L09)*2
                      AND: d(L09-L08) = d(L10-L09) * 0.9

          d(L10-L09) = 3.566-ft
          d(L09-L08) = 3.209-ft
          d(L08-L07) = 2.888-ft
          d(L07-L06) = 2.599-ft
          d(L06-L05) = 2.339-ft
          d(L05-L04) = 2.105-ft
          d(L04-L03) = 1.895-ft
          d(L03-L02) = 1.706-ft
          d(L02-L01) = 1.535-ft

          0.5 * Apex angle: 26.565 
          cot(0.5 * apex angle): 2

Further detail is given in the ARRL Antenna Book under Log Periodic 
Dipole Array.

     Mounting: 1/4-in aluminum plate 10-in X 10-in
               (4) U-bolts to fit 3-in boom & mast
               1/2-in stainless steel bolt, spacers, lockwashers and nuts.


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               ---------------------------------

Bolt through center allows for pivoting of mast for element placement
or repair.

Bolt configuration: Nut-L.Washer-Washer-Boom-Washer-Nut-Washer-Plate-Nut

Any questions, please feel free to contact me at the
following address:

                    Wayne Sarosi
                    995 Alabama Street
                    Titusville, FL 32796

73, KB4YLY/AFA2GN