Force 12 Inc. EF-240S/H Antenne
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.H is for 120 mph winds and assembly detail is on the "H" drawing. The Antenna 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

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Manuel de l'utilisateur
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13 July 2018
IK1UGX Angelo


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