A few of thoughts come to mind about modding this circuit:
1. We know the 7555 can be subsitiuted for lower power consumption in the charging circuit. Frequency is not critical, below 1khz. Does anybody know if it is desirable to have clean DC charging the dish? Or is it better to have this 1khz ac frequency component sent to the dish? There are some easy circuits that will remove most of the ac from the final charging to the dish if this is good for improved performance.
2. Is it desirable to have even higher voltage on the dish? If a higher voltage is good, then a simple diode/capacitor circuit can be used to double, triple the voltage or more. Very low cost.
3. For the antenna signal amplifier, the TLC272 has extremely high inpuit impedance because it is a cmos device with field effect input gate. The next 2 stages of differential amp and linear amp are a second TLC272 (each TLC272 has 2 cmos op amps on the chip). There are several similar cmos op amps in this family starting with the low-cost TLC272 to the TLC277 for high precision. All these devices are capable of taking a very small signal and amplifying it with a minimum amount of interference from the power supply and very low power consumption compared to bipolar op amps. This is why they are the preferred choice of op amps to process the weak ion singnal on the antenna... they give you the best chance of listening to this signal with the least amount of interference from outside noise. If you want to make a substitution, then use another Cmos device or FET device in order to keep the input impedance very high. A simple cmos inverter like the 4001 can be used as a substitute and wired with feedback to act like a linear amp with hand-picked resistors and capacitors to accomplish the same results as the TLC272, but it will be a more simple design. The 4001 inverter version will have the same noise rejection properties as the TLC272, but not the refinements and linearity of the TLC272 op amp version. It may turn out that the 4001 version is adequate, and no need for advanced op amp version of Cmos.
There are also other cmos and FET devices that could be substituted in the signal amplifier stages. If you want to know a good substitution, then look at the cmos and FET catalogs, and find op amps and darlington amps that are available. All these devices consume low power if you don't connect a power hog load to them. And this circuit does not show any power hog load in the output of any of the signal amplifier stages.
4. Ideally these antenna signal amplifiers should be close to the dish and antenna. You may even make a small 30cm circuit board to hold these cmos amplifiers, and connect it to the antenna connection at the teflon bushing. Then put a wire mesh or metal box around this circuit board, and send output wires to the speaker and the meter. In order to keep things simple, the transistor and op amp for the meter and speaker could be mounted on the back of these devices. This way, the sensitive cmos parts could be kept seperate from the higher power noise-maker amplifiers for the speaker and meter.
5. Answer about audio at the speaker: Any audio heard at the speaker will come from one of three sources. 1) If ion signal is being collected on the antenna in a wave pattern that is in the audio range of frequency (20 hz to 15000 hz) then you should hear this sound on the speaker. 2) Electronic noise from the circuitry may be audible on the speaker if this noise gets into the signal circuitry. This noise includes the 1khz charging oscillator frequency, and elecrtonic noise from transistors in the meter and speaker amplifier circuits. 3) Atmospheric interference, which could include who knows what? Could be anything from static electricity to sunspots causing ionisphere interference, or friction from tires rolling on the road sending out static charges. The electronic circuit noise can be minimized by using shielding around the signal amplifiers, and by keeping the connection wire very short between the antenna and the cmos op amps.
6. Final thought is a question for anyone who knows: The antenna signal feeds into 2 op amps which send out a differential signal into the differential amp. But these 2 op amps also have a 3rd op amp shown below in a feedback loop on the lower of the 2 op amps. What is the purpose of this feedback loop? is it only to create a delay that helps reverse the polarity of the lower op amp? Or is it to also act as a filter for certain frequencies seen in the antenna signal?
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