Cushcraft A148-20T Phasing Harness

Phasing Harness for the Cushcraft A148-20T

Parts Needed:
     A few feet of RG-8X Belden or Mini-foam low loss 50 ohm cable.
     A few feet of RG-6 type low loss 75 ohm cable. Belden 9248 will work best because it has a tinned copper        braid, most RG-6 uses an aluminum braid.
     1 UHF TEE connector
     1 UHF double female coupler
     6 PL-259 use silver/teflon or silver/ceramic not rat shack (Radio Shack) cheapies
     which have a phenolic insulating material. Phenolic is very lossy at VHF frequencies.
     6 UG-176 adaptors

Description:
     There are two parts to this harness, a phasing harness and a delay line.

Construction:
     You will need to cut 3 pieces of coax each will be 1/4 wavelength
     at the designed frequency (times the velocity factor of the cable.) 1/4 wave
     sections have a low Q so the center of the 2-meter band was chosen. The
     dimentions are not critical (within a half inch is ok)

     For the two 75 ohm pieces;
     (234/146) x 12 = 19.23 inches
     the velocity factor for 9248 Belden is around 78% or .78 so
     19.23 inches x .78 = about 15 inches

     For the one 50 ohm piece;
     (234/146) x 12 = 19.23 inches
     the velocity factor for RG-8X Belden is around 75% or .76 so
     19.23 inches x .76 = about 14.6 (14 1/2) inches

Assembly:
     See diagram

Changing polarization:
     The illustration will yield RHCP or right hand circular polarization which is pretty
     much the standard. This can be changed if necessary however...
     RHCP = delay line to the horizontal driven element
     LHCP = delay line to vertical driven element
     Axial Polarization = no delay line (Just the 75 ohm phasing harness)

     These rules apply only to dual polarity beams which have the Horizontal and
     Vertical elements at the same spacing, some manufacturers 'stagger' the
     horizontal and vertical bays (like KLM) then things become very different.

By KE9SE

rev 2.0 5/16/2007