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  1. duke37

    Simplest antenna for 5.8GHz 200mW transmitter to allow 100M range

    I would think that a quarter wave antenna would be best. Longer antennas will have some directional characteristics which would be undesirable. Make an antenna a little long and trim it a mm at at time to find the maximum output. You will end up with a wire which is short so replace with the...
  2. duke37

    NiChrome connection assistance needed for my incubator

    Metal clad resistors I do not know what exotic part of the world you inhabit that has no electronic parts distributors or computer auction sites. We, in the UK, can get aluminium sheet from scrap yards which has been recovered from old vehicles.
  3. duke37

    VOX DA5 Amplifier repair help - no power when plugged in

    Unless you know the intimate details of the circuit, it is difficult to say whether excess voltage will damage it. Since the DC input is faulty, I would make a replacement battery box and fit it with a 9V regulator which could be fed from your 16V supply. I have done this with a ghetto...
  4. duke37

    Simplest antenna for 5.8GHz 200mW transmitter to allow 100M range

    Five eigths of a wavelength is a popular size.
  5. duke37

    Blown resistor please help

    My guess is that it is not a resistor. The mark L1 would indicate an inductor as would the wound wire inside. The problem will probably be a short in the circuit causing excess current.
  6. duke37

    Simplest antenna for 5.8GHz 200mW transmitter to allow 100M range

    There is an end effect so the wire is effectively a little longer than its physical dimensions. A thin wire will have litle end effect, a fat one maybe 5% at much lower frequencies. Metal clobber near the antenna will have an effect on its effective length.
  7. duke37

    NiChrome connection assistance needed for my incubator

    You can get metal clad resistors which should be fixed to a heat sink. These could be used bolted to an aluminium plate forming the floor of the chamber. Very little space would be used.
  8. duke37

    Some help on bypass and filtering needed.

    The 9VDC supply should have a filter in it to limit any noise. This is particularly important if it is a switched mode supply. The circuit that is being driven will produce transients from a very low frequency up to many MHz. A PCB will have tracks which are inductances, these can cause high...
  9. duke37

    Half Bridge Converter Question

    Both of the circuits have a capacitance in series with the transformer. With two capacitors the pulse is directly coducted back to the supply or ground line. With one capacitor the pulse is conducted to the ground line only. If this pulse is obtained from the positive supply, then the power...
  10. duke37

    Need signal generator help.

    You seem to have a good transistor with little leakage (or it is not working). The leakage will vary with temperature. If you need a bit more resistance, you can put a fixed resistance in series with the pot. The turn sensitivity will then be similar to the original. I have not used a...
  11. duke37

    detector circuit falling off too quickly

    If the circuit does work, it will be due to the protection diodes rectifying the signal and the opamp amplifying this. The 0.22µF capacitor will be effectively a short circuit at cellphone frequencies so the connctions to the amp will act as a loop aerial, hence the given dimensions.
  12. duke37

    Need signal generator help.

    Just twiddle the pot to get half the supply voltage. You will then find out if the pot is passing too much or too little current. I do not know what the generator + and - are unless it will give an output with a DC bias. In any case, the circuit uses a capacitor which will remove any DC bias.
  13. duke37

    oscillator doesn't oscillator as I expect

    You must have a very good scope to see 93MHz. The high frequency oscillation is due to the coupling loops of your innovative construction. Circuits such as this usually have a capacitor across the emitter resistor to give a low impedance drive to the transistor. Try 100pF to 1000pF
  14. duke37

    Need signal generator help.

    The potentiometer is there to pass the identical current which is leaking through the transistor. Measure the voltage across the emitter/collector connections of the transistor. If the voltage is less than half the supply voltage, then the reistance must be reduced. If the voltage is greater...
  15. duke37

    2N3821 N-channel transistor

    There are some tutorials at the top of this forum. Wikipedia can often supply information. There are book reviews under general electronics chat.
  16. duke37

    Karaoke AMP loss of sound problem

    If it comes back on immediately, I would think it is not a tempeature problem unless it is a dry jount which will cool very quickly Is there an overcurrent circuit wiich resets when the power is turned off?
  17. duke37

    2N3821 N-channel transistor

    I assume XFG1 is an AC signal generator. The signal passes through C1 to the transistor. Will the capacitor impede the signal? When the signal varies the gate voltage, what happens at the source? If the source varies, what happens at the drain? So, what is the voltage gain of the...
  18. duke37

    Function Generator Circuit

    An alternative would be to generate a sine wave using, say, a Wien bridge oscillator. This can be made to have very low distortion. Put the output into a Schmitt trigger to get a square wave. I cannot think of how to get a triangle which is not frequency dependant. Not my field but digital...
  19. duke37

    LEDs Probably the easiest question all year,but help please.

    Welcome to the forum. It is a good idea to state your location in case you wish to work with mains voltage or buy components. There is a tutorial up top which deals with driving leds. Two 2.5V leds with a series resistor will be as much as can be managed from 6V. You could run three on 9V...
  20. duke37

    Need signal generator help.

    The 2N107 is a germanium transistor which will have significant leakage. I presume that R4 is there to pass a similar current so that the resting current through the meter is zero. Fault could be bad transistor, battery connected the wrong way or wireing error. Any resistance will do for...
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