MFJ MFJ-6415, MFJ-6417, MFJ-6420 User Manual

MFJ-64xx Instruction Manual Balanced Line Four Element Colinear Array

INTRODUCTION

The Franklin Array exhibits good gain (~4.5 dB), and delivers better than average signals, even
when hung at only a quarter wavelength (low). This is possible since the array has no vertical
component or vertical directivity, while capture area, and horizontal directivity and gain increase
substantially with the 4-element collinear configuration. The MFJ-64xx arrays must use fully
balanced tuners (MFJ-974H, 974, and 971 series) to tune, apply power to the array, and match
the system to coax input. Use with tuner on other bands is possible, but the Franklin Array
configuration is only on the selected band: 6415, 6417, or 6420.

A further consideration is that this antenna is also quiet, when compared to inverted “V’s” (and
verticals, especially). A reduction of 2 – 3 “S” units of noise may make the difference in that
DX contact you can now hear above the noise!
The added gain means your array presents an effective power gain of “3.” This means 100 watts
applied results in the effective radiated power of ~300 watts! What if you apply 1500 watts out?
Pretty good results for “hanging wire!”

Capture area is another factor in the good performance of the array; The MFJ-64xx has four
times the capture area of a doublet, or inverted vee-type “droopy doublet.”

Once connected and tuned, you’ll find the MFJ 64xx Collinear Array presents a low SWR across
the entire band. However, it only functions as a Franklin Array on “one-band” depending which
band you have purchased. Figure 1 is a generic illustration of the antenna with its shorted stubs
and balanced feed line.

• Always mount or install antennas beyond the reach of adults and
children. Make certain your antenna installation meets RF
exposure guidelines

• Contact with exposed parts of this antenna system can cause RF
burns and other injuries.

• Constructing or erecting antennas where they may contact
electrical power lines can result in injury or even death

Warnings

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MFJ-64xx Instruction Manual Balanced Line Four Element Colinear Array

F

Line to

Balanced

Figure 1 Franklin Collinear Array

F

System Description

Dimension “L1” represents a ½ wave, “L2” represents slightly less than ½ wave, and “F” a ¼ wave, which, in this case is a ¼ wave
stub, used for phase-shifting. The antenna is a “broadside array,” and is bi-directional perpendicular to the run of the wire. A pair of
these antennas at right angles (NE/SW; NW/SE for example) can provide world-wide coverage.

If height is a constraint, this antenna functions better than average at even a bit less than a ¼ wavelength above ground/structure.
However, it really performs best if “hung” at a ½ wave; up to ¾ wave. Higher than that provides diminishing return.

Especially important is keeping the symmetry of the antenna in reference to its ½ wave radiators. They must not sag more than a foot,
with pulled-tight being the best configuration. The feedline can be pulled away at an angle, and some twisting is OK. Stubs should be
tied-off to keep symmetry and damage-free from wind action.

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