MFJ-941EK Tuner Kit
Instruction Manual
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OPERATING INSTRUCTIONS
Fixing Problem Antenna Systems:
The feedpoint impedance for most antennas you'll encounter will swing rapidly
toward some high or low extreme as you move away from resonance. By the
same token, depending on electrical length, the transmission line may take those
extremes and transform them to some new extreme that is completely different!
Fortunately, these problematic situations do occur with some predictability and a
few simple changes can bring them under control. Without getting too technical,
here are some time-tested tips for avoiding trouble in the back yard:
[ ] Never center-feed a half-wave multi-band doublet with balanced line that is
close to an odd multiple of an electrical quarter-wave.
[ ] Never center-feed a full-wave doublet with a balanced line that is close to an
even multiple of an electrical half-wave.
[ ] If the tuner won't match a multi-band antenna on a particular band, change
your feedline length by 1/8-wavelength (as calculated for the affected band).
[ ] Never attempt to load a G5RV on a band below its half-wave design. Better to
short the feed conductors together and load it as a monopole.
[ ] Never attempt to load a 1/2 dipole on a lower-frequency than it was designed
for. Again, better to short the feedline and load it as a monopole.
If you are having a problem with a particular dipole, here are some feedline
lengths to try -- and some to avoid!
160-M Dipole:
Try 35'-60', 170'-195', or 210'-235'. Avoid 130' or 260'
80-M Dipole:
Try 34'-40', 90'-102', or 160'-172'. Avoid 66', 135' or 190'.
40-M Dipole:
Try 42'-52', 73'-83', 112'-123', 145'-155'. Avoid 32', 64', 96', 128'
