South Midlands Communications Group

Trapped Dipole Antenna

Trapped Dipole AntennaThe rhombic antennaThe SMC Trapped Wire Dipole Antenna is a compact and simply operated multi-frequency antenna, designed to provide up to 6 spot frequencies, (dependent upon channel spacing) with bi- or omnidirectional coverage in the HF band. The antenna may be used as shown, with two support units (preferred method) or more economically using a single support structure.

The construction reflects SMC's policy of ensuring long trouble free use, utilising only best quality components. Each antenna is supplied complete with 30m of low loss coaxial feeder incorporating a strain relief arrangement, and fitted with one PL259 UHF connector. The Dipole Centre Junction is formed by a balun unit to ensure matching is achieved.

The elements are constructed of hard drawn copper magnesium multi-strand for durability and high resistance to corrosion.

Frequency Range 2-30 MHz 2 to 6 spot frequencies (depends on frequency spacing).
VSWR Normally better than 1.5 : 1
Polarisation Horizontal
Power Rating Normally up to 250w (up to lkw).
Azimuth Radiation Depends on frequency and height of antenna.
Input Impedance 50 ohm


Antenna elements 7/0.914mm (7/036") or 7/1.118mm (7/044") hard drawn copper strand
Insulators Carbon loaded ultra violet resistant polypropelene
Coaxial cable Centre balun unit with built-in halyard eye and cable suspension unit.
Junction Encapsulated in high grade epoxy resin
Metalwork Stainless steel or plated brass
Coaxial cable Normally 30m UR67 low loss


The most important components of this antenna are the Traps. These are installed in the antenna elements, and provide the means by which multi frequency operation is achieved. The Trap components are fully encapulated in epoxy resin, providing a non-hygrascopic and very strong unit, with proven durability.

Antenna installation kits are available incorporating such items as element end "T" anchors, extension halyards for use in the central support mode.

Although this antenna is offered as a standard product, variations of construction, coaxial cable, connector combinations, or various insulation combinations for hostile environments may be accommodated.

We generally recommend the use of our PA Series lightweight mast to support the Trapped Dipole Antennas. This provides a compact support structure, of ultra light weight, supplied complete with transport holdall and erection tools.

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