Help me design a simple RF receiver which runs on 433Mhz

[HeiFelix]

simple receiver

Hi, Members:

I just begin to design a RF product which runs on 433MHz. The transmitter is made by a SAW resonator in ASK mode. The transmitter is normally in sleep mode and need a signal to wake up it. The wake up signal is in 433Mhz lasted for about 10ms(always in "1" level) and sent by an interrogator 15 meters away. The output power of the interrogator can be up to 200mW.I need to design a schematics which can get this wake up signal in the transmitter but I really have no knowledge about that. The power consumption is required to be < 10uA(possible?) when there is no signal at 433MHz. It should be low cost and simple design. Since the wake up signal is just "1" lasted for 10ms, the quality of signal after demodulation is not so important(I thought).
Please help me and give me a solution directly.

HeiFelix
Thanks

 

[flatulent]

Re: simple receiver

With this low current required and short transmission time your best bet would be a diode detector followed by a low frequency amplifier. You will probably need to bias the detector with a ua or two to improve the sensitivity. Radio enthusiasts will recognize this as the traditional crystal set from 75 years ago. First choice for the diode would be a 1N34 germanium type. Second choice would be a schottky type intended for signal detection use.

 

[HeiFelix]

Re: simple receiver

flatulent:

Thanks for your suggestion. I really have no knowledge about RF. Would you please give me a simple schematic design?

HeiFelix

 

[flatulent]

Re: simple receiver

Here is the general receiver layout. From left to right (the standard way to draw scnematics or block diagrams indicating the signal flow.) antenna input, band pass filter, diode in series, load RC network in shunt, low power amplifier to get the 10 ms pulse, comparator to detect the pulse and produce a logic level to trigger your transmitter.

If you do not have any RF experience this may be more difficult for you but you can still do it. For best performance you will need some expensive test equipment. As a first try, put a wire to a diode in series and put this to your oscilloscope input. See if you can see the pulse. There should be a 200 ohm or so resistor from the node between the diode and the wire to the ground node.

Do not be surprised if you get some of the local AM broadcast stations. This is the reason for the band pass filter in the real design.

 

[HeiFelix]

Re: simple receiver

Hi:
I've tried but very difficult and I need to read a lot of books. Would you please give a simple schematic design?

 

[flatulent]

Re: simple receiver

http://www.alphalink.com.au/~parkerp/noapr97.htm shows a field strength meter schematic. You can modify this by putting an op amp amplifier instead of the meter and if you are getting the broadcast stations put a band pass filter between the antenna and the diodes.

 

[HeiFelix]

Re: simple receiver

Hi, flatulent:

I've made a simple design under your solution and after reading some reference.
Q1 is quite hard to selected because it must be up to 3GHz maybe and low power consumption. D1 and D2 is a double schottky diode(HSMS2812) which may have higher efficiency and more suitable for high frequency but a little expensive(other choice?). AR1(MAX4298) is the most power-saving amplifier which I could find(9uA).
Please check the design for me and make some modification.
I want to know if it is possible to made the static current consumption less than 10uA.
How to directly put the schematic design on the web page here?

HeiFelix

 

[flatulent]

Re: simple receiver

You are stuck by your current consumption limit to not being able to have the first RF stage in your design even though it will increase the sensitivity. Your only path of improvement is to increase the antenna gain on each end of the link if necessary or to increase the transmitter power. the other method is to use a larger capacity battery to raise the 10 uA limit.

For lower cost try any other diodes that are Schottky.

 

[HeiFelix]

Re: simple receiver

Some people said that the diode detector need certain power to start up. Let us say that 300mv (peak to peak) is the minimum gate to start the diode detector. Without the high frequency amplifier, We can imagine that how many gain the transmitter(100mw) and receiver antenna(10 meters away) wiil be and I believe it is impossible. I am afraid the detector can not work without the first amplifer. But if we put the amplifier on it, we must pay the cost of current consumption. Is it possible for an amplifier to work on less than 10uA?

 

[flatulent]

Re: simple receiver

Agilent and others make diodes that need zero bias. You can also put a fraction of a uA through them to improve the sensitivity. Here is an example https://www.spelektroniikka.fi/kuvat/schot8.pdf and another https://www.spelektroniikka.fi/kuvat/schot12.pdf these are application notes showing the details.

On the low current op amps, Maxim and others make them with 2 uA supply current.

 

[HeiFelix]

Re: simple receiver

Hi,

You can also put a fraction of a uA through them to improve the sensitivity.

What does it mean "uA"? If it means a Amplifier. The amplifier should be put before the diode detector or after it?