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Maybe just an LC circuit tuned to 27MHz, and a diode and capacitor, much like the old crystal radio designs? Feed the output to a meter to see the signal level, or to a comparator (might need some amplification beforehand) to trigger an LED at a particular level.
Then it gets a little more complicated.
Google for AD8307 and LM3914, there are some circuits that use those components, that will do what you
need. Stick a tuned circuit and antenna, or a filter in front, for the frequency of interest, otherwise it will pick up signals from a wide bandwidth.
Then it gets a little more complicated.
Google for AD8307 and LM3914, there are some circuits that use those components, that will do what you
need. Stick a tuned circuit and antenna, or a filter in front, for the frequency of interest, otherwise it will pick up signals from a wide bandwidth.
What range are you looking for? A few metres? It doesn't have to be a particularly efficient antenna to pick up RF at close range.
It may work without an antenna.
If you want it for longer range, then the circuit you're looking for is a 27MHz receiver, not a 27MHz RF detector.
What range are you looking for? A few metres? It doesn't have to be a particularly efficient antenna to pick up RF at close range.
It may work without an antenna.
If you want it for longer range, then the circuit you're looking for is a 27MHz receiver, not a 27MHz RF detector.
Thanks. That one looks good. For 27 Mhz band i should include LC network or a filter after RF input, is that right? Any other parameters that should be changed?
A simple circuit like this can be directly built, it only consists of about 3 modules - the voltage-to-LED indicator, the log amp, and the LC circuit or filter.
You could simulate the LC circuit or filter by using any SPICE software.
The voltage-to-LED portion is so tried-and-tested, it is not worth simulating, it is about 20 years old.
Because you're unlikely to find something that will simulate an entire circuit end-to-end, especially when you use 'exotic' ICs like the AD8307, unless AD have a SPICE simulation or similar. Besides, see the number of threads on edaboard where people simulate fine on Proteus, and then their hardware doesn't work because they had so much confidence in the simulation that they didn't even bother to provide power or reset signals to microcontrollers for instance. A simulation is good for areas of uncertainty, but you need to exercise judgement too.
People would rather simulate the important portions, e.g. the filter response for example.
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