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Hero999

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Everything posted by Hero999

  1. 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.
  2. 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. ;)
  3. Thay may have been breaking the law too. It could have been a pirate station.
  4. The more expensive one is rated to 100V. The cheaper one is probably rated to 50V but it doesn't say.
  5. 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).
  6. 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.
  7. 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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