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    JFET "Amplifier". How Would This Work?

    Not sure what you mean by "polarity". The currents in pri and sec are inverted from each other as shown in the diagram. It may have been an amplifier that was designed to produce oscillation as a carrier. Maybe some kind of broadband jammer. Sorry, I am guessing as well. I thought someone...
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    JFET "Amplifier". How Would This Work?

    Thanks for your reply. That is all the info I had on this circuit. Maybe the "not RF" note is wrong. I am still wondering what the purpose of the transformer might be. The primary is 12VDC and the secondary is the source-follower output, but their currents oppose. For discussion, let's assume...
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    JFET "Amplifier". How Would This Work?

    I found this circuit hand drawn in my Dad's old notebook. There were no other notations except "amplifier". Can anyone tell me anything about its possible intended purpose, or how it functions electronically? Why are the JFET's wired in parallel, and what load resistance could this arrangement...
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    Unlicensed Radio That Will Transmit Continuously

    Thanks for the advice so far. It is possible that I may be able to modify one of the devices listed in davenn's post. I believe some businesses now have RFID systems that operate continuously for tracking purposes. I had also thought of retriggering CB radio mic to avoid it timing out. My...
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    Unlicensed Radio That Will Transmit Continuously

    Does anyone know of an unlicensed type of radio that will transmit continuously? Most of the CB type seem to have a time limit controlled by the mic button. I want to broadcast a continuous signal for test purposes. It does not need to be audio modulated. Carrier frequency is not critical. What...
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    Opto Coupled Tunable Coil Circuit - Comments Please

    Yes, actually the resistor at the collector already does that. I was thinking of an earlier emitter side design.
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    Opto Coupled Tunable Coil Circuit - Comments Please

    Non-linearity is sort of what I was looking for. The idea of the transformer is both to current limit the photo-transistor and not load the output of the "tuner" with whatever scratch-built amp I might use. I suppose the transformer could instead be reversed so the 8R side faces the tuner and...
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    Opto Coupled Tunable Coil Circuit - Comments Please

    Thank you for the most recent replies. The theory of the circuit is as follows. The left coil is intended to couple with a nearby EM field source (not shown) which contains a random mix of frequencies. The cap in parallel resonates the coil to a particular range of these frequencies. The opto...
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    Opto Coupled Tunable Coil Circuit - Comments Please

    If I understand your reply correctly, the left coil and cap resonate independently of the transformer primary and its series cap. But the oscillatory signal of the left coil is carried through to the transformer via the opto coupler. Hence the "buffering" effect. Just one more point please...
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    Opto Coupled Tunable Coil Circuit - Comments Please

    I was assuming that the parallel arrangement between the left coil and cap would also extend through the opto coupler to include the right cap and transformer primary. Please correct me if I am wrong regarding this point, or any other features of the circuit.
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    Opto Coupled Tunable Coil Circuit - Comments Please

    Thank you for your reply. The coil is intended to detect ambient audio frequency EM fields. The 2Hz is just to power the LED and provide a gating effect on the detected/tuned EM signal. Do you have any comment on the different action of the two variable caps? The left-hand one tunes both the...
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    Opto Coupled Tunable Coil Circuit - Comments Please

    The circuit below is a thought exercise. The assumption is that an audio frequency signal is induced from an external source into the right-hand coil. At the same time is applied a 2Hz "gating" pulse at a voltage sufficient to power the LED. The two variable caps interactively tune the coil as...
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    Thanks for the additional information. I am surprised at how inexpensive these chips are. https://www.digikey.com/en/product-highlight/c/cypress/psoc-family Another tempting technology to learn.
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    Dana's impressive PSOC approach is way out of my league. But I will keep it on file for motivational purposes. If anyone wants a "ready-made" solution, multiple sine waves can be generated in Audacity (or similar audio editor) and mixed into one track. Brown noise is generated in another track...
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    As per item 4 in my OP, I would like both the amplitude and frequency to be modulated simultaneously by the 5% noise. I looked into scaling factors for handling the fractional numbers, but was not aware the operation was so demanding. For simplicity I will start off using whole integers. Thanks...
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    That gives me a good starting point. With regard to the more complex implementation of fractional frequencies, is there anyway to program a divide-by-ten function for the individual or summed sine waves? For example, 47.2Hz would thereby be derived form 472Hz. I have just one more question. If...
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    That certainly helps with narrowing down the options. I would probably try an 8 bit PIC first. The following product family offers lots of memory and 8 bit DAC, plus PWM if better filtering is required. https://ww1.microchip.com/downloads/en/DeviceDoc/30010211A.pdf The PIC18F27Q43 looks like a...
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    Thank you Harald for your reply. The five summed frequencies would all be below 100Hz (one hundred). So the sampling rate can be low. In this case, what would you recommend? The planned band pass for the noise is about 10Hz to DC. Can I use one LUT for all five sine waves? Not being "audio...
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    Microprocessor Generation of Summed Sine Waves with Random LF Modulation

    I would like to program a micro to do the following: Generate five audio frequency sine waves at different frequencies and amplitudes Sum all the above sine waves into one signal Generate a pseudo-random low frequency waveform at a set amplitude Multiply the summed signal with the LF so the...
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    Series Connect 2 Plug Packs for Split Rail Supply

    It is possible that one supply will "turn on" on before the other. Nonetheless, I believe there is an arrangement of diodes that applies. I have used it before but did not keep the diagram. Maybe also a diode between the two supplies on the common ground link. I would like to figure this out and...
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