Problem with ASK reciever module

[amirahmadian]

Problem with ASK receiver module

Hi everybody.
I'm experimenting with an ASK receiver module (PCR1A 315MHz module. It's Chinese,I think). I just tested the ouput of module in absence of any signal (without any transmitters nearby). I expected the output (Data pin of module) to be constantly low (or high) because there were no signals. But the ouput flickers, I mean it changes to low and quickly comes back to high repeatedly (I monitored the output using an AVR micro). And another strange behaviour, When I touch the antenna (or keep my hand near it) the output becomes constant and it settles down to low.
I've used a simple 20cm wire as the antenna. (I don't know very much about antennas, unfortunately!)
Is something wrong with the module or is there a problem in my antenna,etc ?

Thanks.

 

[biff44]

ASK receivers often use the AGC control voltage to demodulate. If there is no RF signal present, you just get random 1s and 0s out of it because it is triggering on noise. If your transmitted signal is strong enough, but still giving lots of bit errors, you probably have the wrong time constant set up in the AGC circuit for the data rate you are using.

 

[amirahmadian]

Thanks, but I have two questions:
I said when I move my hand near antenna the output of module stops changing. What is the reason?

If there is no RF signal present, you just get random 1s and 0s out of it

Now how can I distinguish random outputs and real outputs!? Suppose I've built a remote control system. When the transmitter is off, reciever gets some random values? How can the reciever realize that is not the real transmitted command?

 

[tony_lth]

That is the protocol (or signaling) to do the handshake between the TX terminal and RX terminal. Before the communications, the TX terminal must transmit a fixed format signal to inform the RX terminal that the data is going to be transmitted. Check the telecommunications textbook.

Your hand changes the antenna VSWR and maybe influence the TX module. Try to adjust the match between tranciver and antenna.

 

[amirahmadian]

That is the protocol (or signaling) to do the handshake between the TX terminal and RX terminal.

Your hand changes the antenna VSWR and maybe influence the TX module.

TX terminal? There are no TX modules. I didn't turn on the transmitter, I just tested the reciever alone, which is why I'm surprised by getting a signal at output.

 

[amirahmadian]

Now I've found something new. :shock:
I changed the power supply and the problem disappeared! I had tested the circuit with batteries and a 5-Volt regulator as the voltage source, then I tested it with an adaptor (and same regulator) and the output of receiver became constant low (I didn't change anything in the circuit). I exprimented again with different batteries (9V, AA batteries) and the problem (flickering of output) happened.
It's confusing! :?:

 

[tony_lth]

Is that some oscilation in your battery circuit and LDO, or LDO circuit itself.
What type is your battery? Some battery have some circuits themselves, so that may caused problems when combining with other circuits.

 

[amirahmadian]

Is that some oscilation in your battery circuit and LDO, or LDO circuit itself.
What type is your battery?

No , I don't think so. Actually, I can't find a circuit in the battery.

What type is your battery?

Simple "Sony AA dry" batteries.

 

[tony_lth]

What is The AA dry battery maximal output current?
What is the adaptor maximal output current?