[ ]
Temporarily fasten each "L" bracket to an end of the hairpin inductor with #6
hardware. The coaxial feedline will be connected to these points later on.
[ ]
Temporarily install the mast-mounting hardware (U-bolt can go on either way).
This completes initial mechanical assembly. Check all fasteners for tightness.
Feedline Installation:
For coax runs up to 70 feet, we recommend using RG8M (or mini-8) 1/4" diameter foam
coax. This light-weight cable is available through most amateur radio dealers and is
available in Radio Shack stores nationwide. RG8M performs well at 50-MHz and will
handle 150 Watts with a reasonable margin of safely. Use the following steps to prepare
your feedline:
[ ]
Strip back the outer insulation 1" and prepare the two conductors as pigtails--as
shown in the diagram below.
RG8M
Lugs
Sealant
[ ]
Install a lug on each pigtail (crimp-type lugs should be crimped
and
soldered).
Pigtail
length should not exceed 1-1/4"--including the lug. Excessively-long pigtails will
detune the matching system.
[ ]
Apply 2-3 thin coats of Seal-All
to the exposed braid to retard water migration into
the cable. If Seal-All is not available, use a rubberized contact cement or a silicon sealer.
Allow sealant to dry thoroughly before handling the feedline.
[ ]
Connect each coax pig-tail to a feedpoint stud using the #6 hardware provided (do
not
use Locktite on these connections). Note that the hairpin is installed on the
bottom
(or
earthward)
side of the boom. When installing the MFJ-1762, the hairpin should be on the
ground side and your coax should drop directly below the hairpin.
Balun:
The MFJ-1762 driven element is balanced. In order to prevent unwanted
radiation from the feedline, we suggest installing a balun at the feedpoint. This need not
be an elaborate or expensive addition--you can make a simple and effective choke-type
balun using the feedline itself. To do this, form a 5-turn coil of RG8M just below the
feedpoint using about 6' cable. Tape the coils together tightly with electrical tape and
secure them to the mast. As an alternative, install three (3) FB43-5621 ferrite cores on the
feedline at the feedpoint. Be sure to secure your feedline to the mast with electrical tape
to provide stress relief at the feedpoint.
