Wellbrook Communications
UNIVERSAL MAGNETIC BALUN (100 kHZ T0 30 MhZ) and ANTENNA FEEDER ISOLATOR (50 kHZ TO 30 MHZ)
The Universal Magnetic Balun UMB is a receiving antenna Balun with a 9:1 impedance ratio.
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The feeder winding is isolated from the antenna to reduce mains borne noise and antenna/feeder interaction. The UMB allows for Longwire, dipole and Terminated Loop to use a coaxial feeder cable without an antenna tuner. The UMB is specifically designed to reduce Mains Borne Noise such as TVs, by ensuring that the antenna earth return path is isolated from the receiver/mains earth. The UMB solves the problem of providing the antenna/feeder impedance match outside the local interference zone, so that the feed to the receiver is free from interference. UMB Features · Frequency range 100kHz to 30MHz · Up to 20dB reduction in Mainsborne Noise compared to other Longwire Baluns · Up to 40dB noise reduction when used with the Antenna Feeder Isolator AFI5030 · Ideal for LW/MW Terminated Loop, with up to 25dB Front-to-Back Ratio · Matches Longwire, dipole, to 50 ohm feeder · Coaxial feeder reduces local interference · Passive with no intermodulation products · Weather-proof, epoxy resin construction · Terminal for connection to a separate earth and a static discharge path to earth ANTENNAS Longwire and dipole antennas are simple to build and provide excellent performance. They can work over a wide frequency range and provide good results during fading. The performance of the antenna is also dependant on the impedance match to the feeder. The antenna impedance can vary by a 10:1 ratio over its frequency range, therefore an impedance matching transformer is essential to prevent signal attenuation due to the high feeder cable capacitance of up to 100pF/metre. Most Longwire matching transformers "Baluns" simply match the high antenna impedance to that of a low impedance feeder cable. However, this has one serious drawback, in that the antenna's return path is the receiver/mains earth, resulting in considerable noise pickup. Thus the advantage of placing the Longwire antenna away from the local interference is lost. In order to reduce interference or noise, it is necessary to provide a separate earth or counterpoise that is free from Mains noise. This separate earth/counterpoise also has to be isolated from the receiver/mains earth to reduce Mains Borne Noise. Longwire Antenna: The Longwire and the UMB should be positioned far away from sources of interference such as fluorescent lights, TVs, computers and electrical wiring. In most cases satisfactory results can be obtained by mounting the antenna 8-10m above ground level and at least 6m from any buildings. The antenna's length should be a minimum of 12m. The UMB should be placed near the ground at the rear of the garden. Using a sloping or "Inverted L" antenna will ensure that the connection to the earth rod will be as short as possible. A separate earth can be a 4ft copper earth rod driven into wet ground away from buried Gas Mains, Electricity cables or other Utilities. The antenna and earth can be connected to either Terminal of the UMB. Dipole antennas: The UMB can be used with a horizontal dipole to provide a broadband match to a 50 ohm feeder. The dipole is connected to the Terminal Posts of the UMB. The dipole should be at least 8 -10m high and 10 -20m long. This configuration should provide excellent short-wave reception. However medium wave and long wave signals will have reduced strength. Terminated Loop: This is unique antenna provides a 20-30dB F/B ratio from 100kHz to 2MHz. UMB provides the correct match for this Loop. Feeder: Up to 50m of RG58C 50W coax cable is recommended. Feeder Isolator AFI 1530 The Wellbrook Antenna Feeder Isolator AFI5030 is designed to reduced mains borne noise from receiver getting into the antenna system, and can be used with any 50 ohm feeder cable and antenna. It is especially effective when used with single ended antennas, such as the Longwire. The AFI5030 is inserted at the receiver end of the feeder cable and uses a separate earth rod isolated from the normal mains earth. However, in most cases the connection to earth can be omitted. The AFI 5030 is fitted with two BNC connectors. N.B.
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Wellbrook
Communications |
Specialists in Broadband Loop Technology!
Designs and specifications are subject to change without notice
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