Originally Posted by J_Player
The Circuit below is what Ivconic posted as a "working LRL". Since it has some standard electronic circuitry, I will give a brief overview for those who are interested. Keep in mind I am not an electronic technician, and I may make some errors.
The basic purpose of the circuitry is to charge the dish positively, and sense minute electrical variations that are picked up on the antenna. The electrical variations sensed on the antenna are amplified and sent directly to the speaker. This means you can hear only variations in the audio range that are sensed on the antenna. The meter is wired to show the amplitude of the audio and non-audio signal variations. There are 4 controls which allow you to adjust the amount of charge on the dish, and to adjust the sensitivity and range that you are sensing on the antenna. This means that you are only measuring relative changes in the signal picked up, not the absolute amount of signal. However, if the controls are left at the same settings, you will see the relative change in signal from one sensing location to another, and from one point in time to another.
Starting with the U1 LM555 at the lower left, all the circuitry around this IC is an oscillator that supplies ac power to the Motorola-Lucent transformet (this is a transformer from a modem card). The secondary side of that transformer is connected so as to put a positive charge on the dish. The 100k potentiometer to the left of the 555 probably adjusts the oscillator frequency. If so, it will ultimately adjust how strong a charge is sent to the dish. This entire charging circuit and it's oscillator has it's own dedicated power supply which is isolated from the remaining sensing circuitry. This is most likely to avoid sending interference from the oscillator to the sensing circuits. I suppose the dish charging circuitry is turned on and off by removing the 9v battery to the left, but a switch could be added to disconnect the battery.
The reciever portion starts with the 30 cm telescoping antenna in the dish. It is shown connected to a wire that passes through a teflon bushing in the center of the dish. It should be said that teflon is one of the best insulators known, and the use of teflon may be crucial for top performance. The physical dimension of this teflon bushing may also be important depending on what voltage the dish is charged to, and if there is an ac frequency component on the dish.
Next we come to the sensor circuitry. (I presume this circuitry is isolated and shielded from the oscillator and dish. All of the sensor circuitry is powered by the two 9v batteries shown at the bottom right. The two voltage regulators provide 8v positive, 8v negative, and a ground. The sensor circuit is also turned on and off by removing the batteries, but a 2-gang switch could be added to turn it on and off. When we trace the wire from the antenna to the 3 ICs to the right, we see the signal is feeding into a 3-IC circuit whose output is sent to a differential amplifier.
Take note, that the differential amplifier has 3 potentiometers, one to control the feedback, and two that adjust the output signal that feeds to the next amplifier stage. This is where the sensitivity and sensing range of this machine is adjusted. After passing through the next amplifier stage at the right, the signal branches toward the speaker and a meter. The speaker has a small power transistor driving it, while the meter has an IC with another adjustment on the input side (appears to be a gain control to keep the meter in the desired range).
A final note about the differential amplifier circuitry: The 3 ICs that initially sense the antenna signal are designed to create a differential signal from the single signal on the antenna. The lower 2 of these 3 ICs, may create a short time delay in addition to inverting the polarity of the signal, depending on the values of the components around the IC. If this is true then this delay can be thought of as a phase shift for any frequency that may be picked up on the antenna, and the degrees of shift would be defined by the frequency sensed. If this portion of the circuit was intended to act as a delay, then it may have a significant influence on the operation of the LRL.
If anyone was to build this circuit, I suppose the mechanical considerations would be to make sure the dish and antenna assembly were sturdy enough to withstand whatever use you put the machine to. I imagine the balance of the finished machine is also important. This machine would be very lightweight, with the heaviest component being the 3 batteries and the meter. The electronics could probably be mounted inside 2 small aluminum boxes attached to an insulator on the back of the dish, and a handle attached to the bottom side of the boxes.
Electrical considerations revolve around the fact that you are measuring minute electrical variations near a charged dish. I would think it is important to wear non-static clothes (no synthetics -- 100% cotton), and keep any other objects that collect static charges away from the machine. Also, I would mount the dish-charging circuit in a seperate metal box from the sensor circuit. And ground both boxes to the sensor ground, while keeping the dish-charging circuit isolated from the box that it is mounted inside. If the charging lead that connects to the dish is longer than about a centimeter, I would shield it with a shield that connects to the box ground.
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