In order to feed two antennas with 50
Ω
line, you'll need to make a simple phasing and
matching harness. The harness is made from readily-available 75
Ω
line. Either solid or
foam-dielectric RG59 is suitable for this purpose. Prepare your harness as follows:
[ ]
Cut
one (1) electrical-wavelength
of RG59. Be sure to use the correct velocity factor
for your particular cable (155-5/16" for 0.66 VF solid dielectric and 186" for 0.79 VF
foam cable). If your cable has a different VF (velocity Factor), use the formula:
Length in Inches = 11800 x VF / Freq. in MHz
[ ]
Install three (3) FB43-5621 ferrite sleeves at each end of the cable.
[ ]
Prepare pigtails with lugs at each end (see previous instructions for RG8M).
[ ]
Cut the RG59 1/4-way down its total length and install PL-259's (at 38'3/4" for 0.66
VF solid or at 46-1/2" for 0.79 VF foam).
[ ]
Splice the RG59 back together using a coaxial type "T" adapter--this becomes the
antenna array's 50-Ohm feedpoint.
[ ]
Connect pigtail ends to the antennas. Note that this "off-center fed" harness shifts
signals 180-degrees out of phase. To correct for this,
be sure to transpose pigtail
connections at the second antenna. If you don't do this, the yagis will be fed out-of-
phase and signals will cancel rather than add! You must install the harness as
shown below:
50-Ohm Feed
RG59
RG8X
Top Antenna
Bottom Antenna
Harness
Portable Operation with the MFJ-1762:
Although designed for permanent roof-top
installations, your MFJ-1762 makes an ideal portable antenna. Its unique construction
permits you to remove the elements in less than a minute for easy storage or travel. To
prepare for transport, simply remove the six #10-32 element mounting screws and detach
each element sections from the boom. The feedline and hairpin assembly may remain
attached. If you remove the U-bolt assembly, elements may be stowed inside the boom.
