GB2285712A

GB2285712A - Magnetic loop antenna

Info

Publication number: GB2285712A
Application number: GB9400764A
Authority: GB
Inventors: Benjamin Edginton
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-01-17
Filing date: 1994-01-17
Publication date: 1995-07-19
Anticipated expiration: 2014-01-17
Also published as: GB2285712B; GB9400764D0

Abstract

A magnetic loop antenna is achieved by using flexible wire 11 for the loop and coupling it to a transceiver feeder 9 with a ferromagnetic transformer instead of the single turn coil normally used. It is tuned at the bottom of the loop 11 with a variable capacitor 14. The loop may be formed from multi-cored wire. It is stable with good bandwidth. It is easy to transport and store and does not require a ground plane or earth which makes it suitable for portable use on boats, vehicles or the top of buildings. <IMAGE>

Description

" IMPROVEMENTS RELATING TO A MAGNETIC LOOP ANTENNA This invention relates to a Magnetic Loop Antenna as used with Radio transmitters and receivers where it is not convenient to erect a full sized antenna.

The Magnetic Loop Antenna is usually constructed of metal tubing which is formed into a Hoop. At the top of this hoop is placed a variable capacitor which is used to tune it to resonance, and at the bottom there is a single turn coupling coil to which the transmission feeder is connected.

The Hoop being formed from tubing is awkward to handle and is also difficult to store and transport.

The coupling Coil is not a very efficient way of transfering R.F. power to the hoop and can not be adjusted when changing bands causing more loss of power.

According to the present invention the improvements have been achieved by first changing the rigid tubular Hoop for multi core flexible wire loop 11, which can be formed into any convenient shape by putting in spreading canes 13, suspending the loop from a mast 12, with the aid of a Lanyard and placing the variable capacitor 14 at the bottom of the loop 11.

The R.F. Power is fed to the wire loop using a Ferromagnetic Transformer constructed as shown in fig,l, using two ferrite tubes 2, through which copper tubes 4, are placed.

The copper tubes are soldered to two copper clad end plates 3, one of which fig 2, the copper laminate is cut through 5, to form the single turn winding which is connected to the two halves of the wire that is used to make the Loop 11.

Insulated wire is wound through the tubes to make another winding no.l, which is tapped at each turn.

Relays can be used to remotely switch the tappings to provide a suitable matched input to the Magnetic Loop allowing the impedance of tne Magnetic Loop 11, to be correctly matched to the feeder 9, coming from the Tranceiver.

This arrangement provides a very efficient means of transfering R.F. power to and from the Loop.

The transformer housing 10, has an eylet at its top to allow it to be attached to a Lanyard so that it can be pulled to the top of a mast 12, when in use.

Nylon lines can also be used to spread out the Loop the ends being fastened to stakes buildings or trees.

By using flexible wire for the Loop 11, it is possible to make very large loops for the lower frequencys, but the length of the wire must be less than one quater wave length in total for the highest frequency that it will have to tune to.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which.

Figure 1 shows the Ferromagnetic Transformer assembly with the tapped winding.

Figure 2 illustrates the cut in the copper cladding.

Figure 3 shows the Improved Magnetic Loop Antenna raised to the top of a mast..

Referring to the drawing the magnetic loop antenna comprises a flexible wire 11, a ferromagnetic transformer Fig 1, and a variable capacitor 14, It is constructed using a Feromagnetic Coupling Transformer fig 1. and situated at the top of the Loop 11 in a case 10 which also contains the switching device when switching is required..

This transformer is used to match the impedance of the feeder end to the wire loop at its lowest point of impedance the half way point and gives a maximum transfer of R.F. power both on Transmitted and Received signals.

The Loop is tuned to resonance with a Variable Capacitor no.14 fig 3 across the ends of the wire loop this capacitor is clipped to the base of the Mast no.12 fig 3. and can be motorised and remote controlled using a control box connected to wire 16..

The feromagnetic transformer fig 1, is wound with insulated wire and tapped at intervals of one turn these tappings are used to make the impedence of the input adjustable when changing bands, and can also be remotely switched by relays ln casing 10..

The transformer casing 10 has an eyelet at its top to allow it to be attached to a Lanyard so that it can be pulled to the top of a mast no 12, Fig 3, when in use.

The loop can be formed into any convenient shape by the use of spreading canes no,13 fig 3, or ropes can be attached to the loop to pull it open and form the loop.

In its present form the wire used for the Loop is multi stranded multi cored wire and this improves the efficiency of the Magnetic Loop antenna by increasing the surface area.

Claims

-CLAIMS

"IMPROVEMENTS RELATING TO A MAGNETIC LOOP ANTENNA" The IMPROVEMENTS have been achieved by first changing the rid tubular Hoop for a multi core flexible wire loop 11, which can be formed into any convenient shape by putting in spreading canes 13, and suspending the loop from a mast 12, with the aid of a Lanyard and placing the variable capacitor 14, at the bottom of the wire loop 11,.

The R.F. Power is fed to the wire loop using a Ferromagnetic Transformer constructed as shown in fig,1, using two ferrite tubes 2, through which copper tubes 4, are placed.

The copper tubes are soldered to two copper clad end plates 3, one of which fig 2, the copper laminat is cut through 5, to form the single turn winding which is connected to the two halves of the wire that is used to make the Loop 11.

Insulated wire is now wound through the tubes to make another winding no.l, which is tapped at each turn.

Relays can be used to remotely switch the tappings to provide a suitable input to the Magnetic Loop allowing the impedance of the Magnetic Loop 11, to be correctly matched to the feeder 9, coming from the Transmitter.

This arrangement provides a very efficient means of transfering R.F. power to and from the Loop and compensates for any slight loss created by distorting the shape of the wire that makes up the Loop 11..

The transformer housing 10, has an eyelet at its top to allow it to be attached to a Lanyard so that it can be pulled to the top of a mast no 12, fig 3, when in use.

The loop can be formed into any convenient shape by the use of canes no,l3 fig 3, or ropes which can be attached to the loop to pull it open.
2 A Magnetic Loop Antenna as claimed in I wherin by using multi core cable for the loop an improved efficiency can be achieved.
3 A Magnetic Loop ntea as claimed in 1 G 2 wherin the loop can be erected on a Boat ehip or Vehicle for Amateur or Commercial u.
4 A Magnetic Loop Antenna as claimed in 1 that can be remotely tuned using a motorised Variable Capacitor and controler.
5 A Magnetic Loop Antenna as claimed in 1 or 2, or s that can be automatically tuned by a Computer or microprocessor.
6 A portable Magnetic Loop Antenna as Claimed in 1,or 2,or 3 4 or 5 or 8 that can be used in a position where a ground plain or good earth is not available.
7 A Magnetic loop Antenna as Claimed in 1 or 3 that has an adjustable input impedance and does not require an additional tuning unit although one can sometimes be used with advantage.
8 A portable Magnetic Loop Antenna as claimed in 1 or 3 or 6 or 4,or 6,that can be easily disassemble and packed away for transportation or storage.
9 A Magnetic Loop Antenna as claimed in 1 or 3 or 6 or 8 that is constructed with multi core wire supported from a frame or mast with a variable capacitor at the top and a ferromagnetic transformer at the bottom
10 A Magnetic Loop Antenna as claimed in 1 or 3, in which the size of loop can be altered to give the best results for a given priority band.
11 A Magnetic Loop Antenna as claimed in 1 or 9 that can contain additional flexible wire loops that can be switched in to operation when required.
12 A Magnetic Loop Antenna as claimed in 1 or 9 or 11 that can be changed to different bands by switching in fixed capacitors of selected values.
13 A Magnetic Loop Antenna as claimed in 1 or 9 or 11 that can be mounted horizontally 14 An improved magnetic loop antenna substantially as described herin with reference to Figure 1-3 of the accompanying drawing.