A
Anonymous
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refs: my posts of 21 Jan 02 "coplanar DD loop disclosure" and DD loop disclosures (long)". Also Frank Wallis' post of 17 Jan 02 "coil improvement".
In a conventional DD loop, two "fat D's" overlap each other in order to produce a condition of induction balance. This arrangement has certain desirable characteristics. The disadvantages include greater assembly thickness as compared to coplanar construction, and difficulty in achieving and maintaining induction balance due to the close proximity of the coils in a region where there is pronounced lack of symmetry in two planes.
As a thought experiment, suppose we replace the fat-D overlapping transmitter coil with two coils wired in series: a skinny D outside the receiver coil, and a long narrow elliptical coil just inside the receiver coil. If the number of turns and the geometry are scaled properly, this will produce a condition of induction balance together with a response field which is a crude approximation to that of a traditional double-D.
It will be appreciated that a similar result could be achieved by reversing the roles of receiver circuit and transmitter circuit.
Although these are coplanar arrangements, they are not concentric, and good geometry may be difficult to achieve. However, by combining these two ideas, a concentric arrangement is possible.
Suppose we have a main transmitter coil in the shape of a slightly narrowed D, and a main receiver coil of similar shape. Position these coils on a plane with appreciable space in between the flats of the D's. Of course there is no condition of induction balance, and the coupling into the receiver is negative.
Now, wind a long narrow receiver coil and transmit coil of generally similar size and shape, either together on the same mandrel, or on different mandrels. This arrangement is well known in the industry, although the second winding is usually referred to as "feedback" rather than "transmit".
Place the long skinnies between the two D's, and wire the coils in series with their corresponding D-shaped coils, phased the same as the D's. If the number of turns and the geometry are correct, the positive voltage coupled into the long skinny receiver will balance the negative voltage coupled into the D-receiver.
This arrangement, unlike the coplanar system I disclosed on the 21st, has a symmetrical response pattern and good pinpointing characteristics close to the loop on small shallow targets. It retains the well-known advantage of reduced ground interference in comparison to axially symmetrical loops. The combination of true coplanarity and lateral symmetry of the transmit and receiver coil circuits improves the accuracy of schemes which rely on inductance pulling compensation for improved operation in black sand.
If one adds secondary coils on the D's (as described in my post of the 21st), it is possible to adjust the loop response pattern to enhance shallow targets or to enhance deeper targets. However, the effort expended would probably not justify the results.
--Dave J.
In a conventional DD loop, two "fat D's" overlap each other in order to produce a condition of induction balance. This arrangement has certain desirable characteristics. The disadvantages include greater assembly thickness as compared to coplanar construction, and difficulty in achieving and maintaining induction balance due to the close proximity of the coils in a region where there is pronounced lack of symmetry in two planes.
As a thought experiment, suppose we replace the fat-D overlapping transmitter coil with two coils wired in series: a skinny D outside the receiver coil, and a long narrow elliptical coil just inside the receiver coil. If the number of turns and the geometry are scaled properly, this will produce a condition of induction balance together with a response field which is a crude approximation to that of a traditional double-D.
It will be appreciated that a similar result could be achieved by reversing the roles of receiver circuit and transmitter circuit.
Although these are coplanar arrangements, they are not concentric, and good geometry may be difficult to achieve. However, by combining these two ideas, a concentric arrangement is possible.
Suppose we have a main transmitter coil in the shape of a slightly narrowed D, and a main receiver coil of similar shape. Position these coils on a plane with appreciable space in between the flats of the D's. Of course there is no condition of induction balance, and the coupling into the receiver is negative.
Now, wind a long narrow receiver coil and transmit coil of generally similar size and shape, either together on the same mandrel, or on different mandrels. This arrangement is well known in the industry, although the second winding is usually referred to as "feedback" rather than "transmit".
Place the long skinnies between the two D's, and wire the coils in series with their corresponding D-shaped coils, phased the same as the D's. If the number of turns and the geometry are correct, the positive voltage coupled into the long skinny receiver will balance the negative voltage coupled into the D-receiver.
This arrangement, unlike the coplanar system I disclosed on the 21st, has a symmetrical response pattern and good pinpointing characteristics close to the loop on small shallow targets. It retains the well-known advantage of reduced ground interference in comparison to axially symmetrical loops. The combination of true coplanarity and lateral symmetry of the transmit and receiver coil circuits improves the accuracy of schemes which rely on inductance pulling compensation for improved operation in black sand.
If one adds secondary coils on the D's (as described in my post of the 21st), it is possible to adjust the loop response pattern to enhance shallow targets or to enhance deeper targets. However, the effort expended would probably not justify the results.
--Dave J.
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