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  1. duke37

    Wireless power transmission

    Sorry about not reading your post properly, I saw youtube and passed the references by as I have narrow band, not broadband! The two inductors are in series and should be coupled closely together. The centre is at a constant potential, so when the voltage on one side goes down, the voltage at...
  2. duke37

    differential op amp to measure current

    I do not know whether the transformer will be suitable. I would guess that the duty cycle should be taken as 1. If the load is resistive, you could measure voltage. If you put the current transformer before the rectifier, there will be no DC component.
  3. duke37

    Wireless power transmission

    C2 and C3 will both charge when switched on but they will not be identical and the fets will also differ. The fet that passes the most current will pull its drain voltage down which will lift the voltage at the other end of the inductor. This will pull the gate voltage more positive on the...
  4. duke37

    Wireless power transmission

    You have not said where you got the circuit from, did you read what I posted? The two coils you show should be closely coupled together with the centre connction to the power supply. There may be enough interwinding capacitance to eliminate the tuning capacitor. An oscillator is an...
  5. duke37

    frequency of oscillation in a twin t oscillator

    This should have been answered by an Australian, they are upside down! So it is an asymetrical circuit with different resistances so you get SQRT(R1*R2) F = 1/(2*pi)*SQRT(1/(R1*R2*C1*C2)) R1=15k R2=1.5k C1=100n = 1E-7 C2=10n = 1E-8 using the notation that E is 10 to the power of...
  6. duke37

    UK Simple circuit, can anyone make it for me?

    a.mlw.walker You have made 31 posts, non as far as I see helpful to anyone else. CocaCola has posted 2828 times, sharing his knowledge over a long time. Please do not impugn his integrity. Duke
  7. duke37

    Wireless power transmission

    Where did you get the circuit from? The two inductors L1 and L2 should idealy be wound with bifilar wire so they have very tight coupling between the two halves of the coil The circuit works as an oscillator tuned by C4 and with C2 and C3 providing the feedback. R5 will limit the output.
  8. duke37

    Help me diagnose circuit problem

    Power = V * I * cos(theta) where theta is the phase angle. A resistive load will give a phase angle of 0, reactive loads will give lower power even with the same current. A diode with 0.007V drop would be worth a fortune. I suggest you buy 1000 ballasts, take the diodes out and sell them for...
  9. duke37

    For what value of L, will this circuit resonate at 332kHz?

    Hi Laplace, you made my mind boggle 55 years ago. You seem to be able to do it still. I would have checked all that the switches were all correct and working properly and, if only one frequency was involved, then the contacts could be bridged so there would be no likelyhood for poor contact...
  10. duke37

    Help with dropping 20 volts for 8kw AC or DC

    A voltage divider will waste more energy than a simple resistor and so generate more heat. You have not said what the load is or how much ripple is permissible. A controlled bridge could be made to chop the output waveform but the ripple will be very high unless a capacitor half the size of a...
  11. duke37

    555 Mosfet driver problems

    Have you tried a led and resistor between the source and gate as I suggested in #5?
  12. duke37

    Audio induction coil

    Wikipedia has a page on audio induction loops and refers to a British Standard which can be used to design a loop. It can be simple and crude or complex and expensive. You will need a device with a pick-up coil and an amplifier - maybe a scrap hearing aid will do.
  13. duke37

    Oscilloscope does not display the correct waveform RIM Rog 7A

    I presume that the high frequency response can be optimised by adjusting the amount of inductance.
  14. duke37

    Oscilloscope does not display the correct waveform RIM Rog 7A

    I see no potentiometer near L1 but there is near L2 and L3.. This looks as if it should be adjusted to get sync equaly on positive and negative transitions. There is a 320 ohm resistor in the picture. This may be wire wound and used as an inductor. L2 and L3 are labelled 'rot' which may be...
  15. duke37

    Roberts Revival - is it broken????

    Check the battery voltage when operating the set, perhaps you have one of more faulty cells. Note that a DAB set is fairly thirsty. 7V seems a strange voltage, 4 alkaline cells would give about 5V so a 6V supply should be OK.
  16. duke37

    Audio induction coil

    Audio loops for deaf aids use quite a large current. The bigger the loop, the larger the current requied. The current can be reduced if multiple turns are used and this is often used to get a resistance nearer to the load required by the amplifier. An approximate current drive can be made by...
  17. duke37

    Oscilloscope does not display the correct waveform RIM Rog 7A

    8mhz seems a very low frequency, 8MHz is more likely. The resistor is there to develop a voltage in the amplifier. No resistor, no amplification. I could not tell you the best capacitors to get. I only know that vintage radio enthusiasts will often change all the old capacitors and will...
  18. duke37

    Oscilloscope does not display the correct waveform RIM Rog 7A

    I think the inductor would expand the range by 50% or so, rough guess. Find out what the specification of the scope is. I looked up the plugs and sockets on Wikipedia. The SO-239 socket matches the PL259 plug.
  19. duke37

    Oscilloscope does not display the correct waveform RIM Rog 7A

    Sorry I got the number wrong. A resistor and inductor in series is used to create the correct impedance to expand the frequency response. If you have broken the inductor, then you could replace it with a short but the high frequency response will be compromised.
  20. duke37

    Summing amp help

    I cannot get at your zip file. What is wrong with a simple picture? I would make a virtual earth amplifier with input resistors chosen to set the gain.
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