Using an MFJ 259B or better, connect a
coaxial tee to the analyzer. On one side of the tee
install a 50ohm termination resistor. The other side of the tee
will be connected to the coax under test. For example, a 1/4
wave length piece of coax at resonance will show the following
readings on the MFJ 259B:
Next, cut a piece of RG-58/U PE VF.66
10' long. At one end of the coax trim back a couple of inches of
the PVC jacket and separate the shield from the center conductor. This
end will feed into the other side of the coaxial tee (center to center
and shield to ground) on the MFJ. At the other end of the coax,
remove a couple of inches of the PVC jacket, slide the shield back,
strip 1" of the PE from the center conductor and short the shield to
the center conductor.
Then, turn the tune knob on the MFJ to
18.050. You will notice that the piece of coax is not
resonate. Turn the tune knob slowly down in frequency until the
display reads 49ohm, 1:1 SWR and X=0. You should end up
somewhere around 16.200.
Use this formula to determine how much
of the 10' piece of coax you will have to trim off.
In this example: 16.200/18.050 =
.897. Take 10' x .897 = 8.970'. This is the length that your 10'
piece of coax should be trimmed to resonate at 18.050. Check again
with the MFJ and repeat as necessary.
When you have resonated your piece of
coax, only the center conductor will be used at the feed point.
The other end will remain shorted.
The end result should be an electrical
1/4 wave length with over a 30% reduction in size as compared with an
conventional awg wire for antenna elements.