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Everything posted by Hero999

  1. It's an NTC (negative temperature coefficient) resistor. When it's cold it has a fairly high resistance, as it heats up its resistance drops. It's used a an inrush current limiter. When the power is first applied it's cold and its high resistance limits the current, as it warms up its resistance drops, allowing the full current to flow. It's needed because the filter capacitor across the rectifier on the mains inlet draws a huge current when the power is applied. The chances are other components have failed, I recommend checking the rectifier and filter capacitor (both value and ESR), if you don't have an ESR meter (value alone isnt' good enough) then replace the capacitor as a matter of course. Failure of the filter capacitor, rectifier or chopper MOSFET(s) could cause the NTC resistor to fail. Additionally failure of the filter capacitor can cause the rectifier and MOSFET(s) to fail and failure of the MOSFET(s) can cause the rectifier and associated components to fail. Because of this, it can be pretty hard to find out what went wrong first. There's also a good chance many other components have failed rendering it beyond economical repair.
  2. Remove the tracker device. Why is the tracker there anyway? You say you're being stalked, report it to the police. Do you live in a country with an authoritarian government? Perhaps you're being spied on by the secret police. Just inspect your car for tracking devices before you drive.
  3. The same way they can track the tracker. They use a direction finder and field strength meter to get a rough direction and distance between them and you. If anything, the jammer is going to make their life easier not harder as the signal from your car will be stronger.
  4. Because that's what inductors do: they try to keep the current constant. Think of a flywheel: difficult to get spinning and hard to stop once spinning. An inductor stores energy in the form of a magnetic field which takes energy to build and releases energy when it collapses. When there's no current flowing through the coil and its energised, energy is needed to build the field. If the current is suddenly interrupted, the field collapses which induces a high voltage spike which forces the current to carry on flowing by arcing over the switch contact.
  5. Hero999

    Re: Relay

    What's an SPS relay? Single Pole Single What? Throw, I'd guess? No conversion is necessary, just only use one of the poles or better, connect them in parallel to increase relay life.
  6. The noise is nothing to do with the high voltage protection, it is generated by the high frequency switching transistor in the supply and the mains. Extra filtering will reduce the noise but there's no way to eliminate it completely.
  7. It's not possible. Cheap AC clamp meters use a current transformer principle which only works on AC currents, for DC you need a hall effect sensor. A DC clamp meter will cost more but that's life. ;)
  8. Thay may have been breaking the law too. It could have been a pirate station.
  9. The more expensive one is rated to 100V. The cheaper one is probably rated to 50V but it doesn't say.
  10. What's the point of the 10k resistor? It's in parallel with 1R so it's not going to make any difference. He needs something to trigger the alarm, he could configure the other half of the op-amp as a comparator with a small piezo buzzer connected to the output so it makes a noise when the LNB is stolen. Watch the current consumption of the buzzer though, the LM358 can only source 10mA and loading the power supply too much is probably a bad idea. Luckily you can get <10mA piezos but they're not that loud. If you want a very loud siren to sound when it's stolen, you need an external power supply whether this be a battery or a mains power supply (wall wart).
  11. A wireless doorbell? Is he deaf or is it just that he can't understand you? If he can't hear then you could add a motor with a weight on the shaft to the wireless doorbell to make it vibrate as well as chime.
  12. That won't work, you need to measure the DC current flowing though the co-ax, not just the voltage. You need to break the shield and wire the resistor in series. The break and the resistor need to be as small as possible to avoid ruining the properties of the transmission line. I'd recommend a low inductance thin metal film surface mount resistor. I'd also recommend adding a filter capacitor and possibly ferrite beads to the input of the amplifier, op-amps aren't designed to work at these sorts of frequencies and might do funny things when exposed to an 18GHz signal.
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