One is used as the antenna input with the outer sleeve connected to ground and the center pin connected to the 100 pfd C1 capacitor. The two 1/8 inch audio connectors replace the more expensive BNC. A cheaper alternative would be four 3/4 inch 6/32 screws and nuts to form the standoffs. It was necessary to glue two together to make the 3/4 inch clearance needed.
Vlf receiver circuits Pc#
The four corner mounting holes on the PC board were enlarged slightly and used to make legs that would allow the receiver to sit on a flat surface. There are no feedback problems with these short connections. The 50K gain pot is connected between R7 and pin 1 of the second TL082 IC. The 10K tuning pot is connected between ground and the end of R5. There is no need to use shielded wire since the connections are short. Short pieces of bare copper wire are used to connect the pots. The pots should be rotated to position the tabs close to the corresponding points on the circuit board where the connections are to be made. All parts should be mounted on the PC board and soldered carefully before the pots are put in place. Some small washers should be placed on the shafts to lift the pots slightly off the PC board to prevent shorting to the copper foil. The shafts on the potentiometers are usually long and should be cut off with a hacksaw to about 3/4 of an inch. The second 3/8 inch hole is made 3/4 inch from the right edge and 5/8 inch from the front edge of the board. The third hole is made with a 3/8 inch drill 1 and 3/4 inches from the left edge and 1 inch from the back of the board. The second 1/4 inch hole is made 1 and a 1/4 inch from the right side and 7/8 inch from the back edge. The first 1/4 inch hole is made 3/4 of an inch from the left side of the board and 1 inch from the back edge. The circuit board is a new version with an overlay showing parts placement. It would be well to check the polarity of the leads with a voltmeter before soldering. The white lead with a black tracer is connected to the junction of C8 and R14. The white lead from the transformer is connected to the junction of. Capacitors C8 and C9 complete the power supply circuit. The two resistors nicely replace the diodes D4 and D5 in the original Gyrator II circuit. This may seem like a short circuit, however only about 25 milliamps flow through the resistors.
Vlf receiver circuits series#
To simulate a center tap, I used two 180 ohm resistors in series across the 9 volt DC transformers, with the common center point connected to ground. I modified the power supply circuit to use a 9 volt DC wall plug transformer. Radio Shack does not carry a center tapped 12 volt AC wall plug transformer. Since there is no convenient mounting place on the board for this type of transformer, I decided to use a wall plug transformer. The previous Gyrator II used a center tapped 12 volt AC transformer and two diodes to form a bipolar power supply. The basic circuit is the same as the previous Gyrator II circuit with the exception of the power supply. The only modification to the circuit board is the need to drill four holes to mount two connectors and two potentiometers. All parts are mounted on the circuit board. Also eliminated is the metal working associated with drilling mounting holes in the cabinet. This simplified version eliminates the metal cabinet and expensive BNC connectors. The number of parts has been reduced to the essentials. The Minimal Gyrator II receiver described here is an attempt to show a lower parts cost receiver for solar monitoring that would be a suitable school project. The Gyrator II VLF receiver is described in another section of the SID equipment.