A
Anonymous
Guest
This is probably prior art, but here goes anyhow.
The customary way of building a DD loop is to wind two D-shaped coils of similar shape, but usually different inductance. Then one coil is installed in the assembly overlapping the other such that a condition of induction balance is produced.
The advantages of this construction are simplicity and approximate bilateral symmetry. The disadvantages are lack of coplanarity which leads to the need for a housing thicker than would otherwise be required, difficulty in achieving a good reactive null due to the overlap of the coils, and difficulty in maintaining reactive balance due to the overlap of the coils as well as asymmetry of the assembly in the vertical plane.
An alternative construction is to wind a "feedback" coil either inside or outside the receiver coil, in the manner which is customary in concentric coplanar loop contruction. The feedback coil is wired in series with the transmitter in the manner which is customary in concentric loop construction.
If the proper amount of feedback is furnished, the coils will balance lying in the same plane without crossover. This makes thinner contruction possible, makes nulling easier, and makes it easier to produce a loop which will be stable. Another advantage is that the dipole created by the feedback winding is in phase with the transmit winding (the receiver being entirely within a negative field zone), increasing the total dipole moment of the transmit field.
One disadvantage is that the bilateral symmetry is broken. In practice, this is probably a disadvantage of no major importance.
Another disadvantage is that the response close to the loop is highly distorted, which can impair target identification and pinpointing. The problem can be partially resolved by adding additional "pinpoint" coils along the centerline either between the D's or in a plane in front of the D's, but the benefit might not warrant the additional complexity.
Some of the double-D tricks mentioned in my earlier post are difficult or impossible to do with the coplanar arrangement.
--Dave J.
The customary way of building a DD loop is to wind two D-shaped coils of similar shape, but usually different inductance. Then one coil is installed in the assembly overlapping the other such that a condition of induction balance is produced.
The advantages of this construction are simplicity and approximate bilateral symmetry. The disadvantages are lack of coplanarity which leads to the need for a housing thicker than would otherwise be required, difficulty in achieving a good reactive null due to the overlap of the coils, and difficulty in maintaining reactive balance due to the overlap of the coils as well as asymmetry of the assembly in the vertical plane.
An alternative construction is to wind a "feedback" coil either inside or outside the receiver coil, in the manner which is customary in concentric coplanar loop contruction. The feedback coil is wired in series with the transmitter in the manner which is customary in concentric loop construction.
If the proper amount of feedback is furnished, the coils will balance lying in the same plane without crossover. This makes thinner contruction possible, makes nulling easier, and makes it easier to produce a loop which will be stable. Another advantage is that the dipole created by the feedback winding is in phase with the transmit winding (the receiver being entirely within a negative field zone), increasing the total dipole moment of the transmit field.
One disadvantage is that the bilateral symmetry is broken. In practice, this is probably a disadvantage of no major importance.
Another disadvantage is that the response close to the loop is highly distorted, which can impair target identification and pinpointing. The problem can be partially resolved by adding additional "pinpoint" coils along the centerline either between the D's or in a plane in front of the D's, but the benefit might not warrant the additional complexity.
Some of the double-D tricks mentioned in my earlier post are difficult or impossible to do with the coplanar arrangement.
--Dave J.