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I have a signal that consists of a 13MHz RF signal inside a pulse envelope (around 100ms on, 300ms off). I want to convert this to a 0-5V pulse that will just tell me when the primary RF signal is active ( i.e. ignoring the RF component, just taking the pulse).

I was thinking of using a bridge rectifier and then and averaging this with an earth (using an op-amp, I guess?) and then subsequently using a relay to turn this signal into a 0-5V signal. Does that sound feasible? Am I missing an easier way?

Many thanks for your help.

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  • \$\begingroup\$ I think you're missing an easier way where all you need to do is use a half-wave rectifier, a capacitor, a couple of resistors, and a transistor to get the whole thing done. What's the amplitude of the RF pulse and where's it coming from? If it's from a signal generator of some sort, what's its output impedance? \$\endgroup\$
    – EM Fields
    Commented Jun 9, 2015 at 23:46
  • \$\begingroup\$ Thanks for the reply. RF pulse is somewhere between 0 and 5 V p-p. Amplitude of this signal is related to the generator's output power so it can vary. Output impedance isn't noted, so I assume 50 Ohm? \$\endgroup\$
    – CammyDoo
    Commented Jun 12, 2015 at 0:22
  • \$\begingroup\$ OK, but what's the lowest amplitude pulse you want to detect? \$\endgroup\$
    – EM Fields
    Commented Jun 12, 2015 at 6:30
  • \$\begingroup\$ 100mv or so would be sufficient, i think. \$\endgroup\$
    – CammyDoo
    Commented Jun 14, 2015 at 23:47

1 Answer 1

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AM demodulation consists of a diode detector and this will work just fine for getting the envelope of the signal i.e. the pulse envelope. Don't use a bridge rectifier these are notoriously slow and won't rectify properly with anything much faster than a few kHz. Use a BAS16 or IN4148 followed by a resistor to 0V and a capacitor in parallel.

You haven't stated the amplitude of the RF so a few extra precautions may be needed.

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  • \$\begingroup\$ AM demodulation - of course. It's only a max of 5V p-p, so I wouldn't have thought anything fancy would be required? i didn't know that bridge rectifiers were slow. That's a good tip. \$\endgroup\$
    – CammyDoo
    Commented Jun 12, 2015 at 0:24

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