MFJ-941E Versa Tuner II
5
A problem also occurs on 40 meters with this antenna example. The feedline is now a multiple of
a half-wave (60 to 70 foot) and connects to a full-wave high impedance antenna (100 to 140 foot).
The half-wave line repeats the high antenna impedance at the tuner. The antenna system looks
like several thousand Ohms at the tuner on 40 meters. The following suggestions will reduce
the difficulty in matching an antenna with a tuner:
1.
Never center feed a half-wave multi-band antenna with a high impedance feedline that is
close to an odd multiple of a quarter-wave long.
2.
Never center feed a full-wave antenna with any feedline close to a multiple of a half-wave
long.
3.
If a tuner will not tune a multi-band antenna, add or subtract 1/8 wave of feedline (for the
band that won't tune) and try again.
4.
Never try to load a G5RV or center fed dipole on a band below the half-wave design
frequency. If you want to operate an 80 meter antenna on 160 meters, feed either or both
conductors as a longwire against the station ground.
To avoid problems matching or feeding any dipole antenna with high impedance lines, keep the
lines around these lengths
[
The worst possible line lengths are shown in brackets
]
:
160 meter
35-60, 170-195 or 210-235 feet.
[
Avoid 130, 260 ft
]
80 meter
34-40, 90-102 or 160-172 feet.
[
Avoid 66, 135, 190 ft
]
40 meter
42-52, 73-83, 112-123 or 145-155 feet.
[
Avoid 32, 64, 96, 128 ft
]
NOTE:
Some trimming or adding of line may be necessary to accommodate higher bands.
WARNING:
To avoid problems, a dipole antenna should be a full half-wave on the lowest band.
On 160 meters, an 80 or 40 meter antenna fed the normal way will be extremely reactive with only
a few Ohms of feedpoint resistance. Trying to load an 80 meter (or higher frequency) antenna on
160 meters can be a disaster for both your signal and the tuner. The best way to operate 160 with
an 80 or 40 meter antenna is to load either or both feedline wires (in parallel) as a longwire. The
antenna will act like a "T" antenna worked against the station ground.
Technical Assistance
If you have any problem with this unit first check the appropriate section of this manual. If the manual does
not reference your problem or your problem is not solved by reading the manual, you may call MFJ
Technical Service at
601-323-0549
or the MFJ Factory at
601-323-5869
. You will be best helped if you
have your unit, manual and all information on your station handy so you can answer any questions the
technicians may ask.
You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial Park Road, Starkville, MS
39759; by Facsimile to 601-323-6551; or by email to techinfo@mfjenterprises.com. Send a complete
description of your problem, an explanation of exactly how you are using your unit, and a complete
description of your station.
Schematic:
(2 pages)
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