Force 12 Inc. EF-240S/H Antenne
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40 Meter Linear Loaded 2 element Yagi
The Elite Force EF-240S
is 2 element 40 meter yagi Antenna
utilizing shortened 40 meter elements and is shown in the
photo above a Sigma-280 Magnum 2 element 80/75 mtr Yagi.
Each element is the EF-140S, which is 37.8' long, or 56% of
full size. The EF-140S element utilizes a single linear
loading system that is physically located above the element
in a "V" format. The elements use FORCE 12's linear loading
design, which provides the highest feed point impedance and
broadest bandwidth of any shortened Antenna
to date. The 2
element yagi is a driver and reflector design. Both elements
are physically identical and their function is determined by
how each is tuned. The reflector is tuned lower in frequency
than the driver and the driver is tuned to the center
frequency of desired operation. The reflector element has a
jumper across the center feed point and the driver receives
the feed line. As of July, 1998, the standard element design
has been strengthened using an additional inner liner of
.750" and .875" at the point of maximum element compression
(this is the first tubing junction out from the center).
This increased the rating for both to 95 mph. The EF-240S
is for 120 mph winds and assembly detail is on the "H" drawing.
is shipped in sub-assemblies and each assembly
section is appropriately identified. Each element is divided
into two (2) halves: "A" and "B". Assembly requires only
that the element side identifications are matched, such as
"Al-Al; A2-A2; Bl-Bl", etc. to construct an element. All the
rivet holes are pre-drilled and will align exactly when the
proper sections are matched. Sometimes the elements are
built in large lots and are controlled with a consecutive
manufacturing number. This number is left on the elements to
enable matching the halves together (i.e. 2A and 2B; 5A and
5B; 9A and 9B; etc.) Any pair makes a full element. The boom
is in several sections and adjacent sections are marked
"A-A", "B-B", etc. Matching up the sections completes the boom.
The expected 2:1 VSWR bandwidth of the EF-240S
is more than
100 kHz at the Antenna
, typically being about 130 kHz. After
a typical run of coax, the slight amount of loss in the coax
will widen the VSWR response of the Antenna
. This is normal.
The driver can be set for lowest VSWR by moving the tuning
jumpers on each side of the element equal amounts until the
desired frequency/low VSWR is obtained. The input impedance
at the feed point is less than 50 ohms and is stepped up to
50 ohms by using a hairpin match mounted across the feed
point. This hairpin is in the form of a "helical hairpin",
or coil, as a typical hairpin would be physically too large.
The match to 50 ohms is adjusted by making the spacing on
Manuel de l'utilisateur
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13 July 2018