Wireless data link problem (433MHz, ASK modulation)

[Regnum]

I have a couple of Wenshing Rx/Tx modules for data communication, working in the 433Mhz band.

Wenshing datasheets say they're ASK modulation, but I think they may specifically be OOK (no carrier during tranmission of zero)

Due to low-power requirements I need the transmitter module to be off the most of the time, but the problem arises when the transmitter is not sending data (or it's switched off) for over 200msec, so the receiver outgoing signal becomes a digital-level noise... (I'm not a RF-man, but I infer it's an OOK module, so when carrier is absent for 200msec the AGC goes to maximum and the receiver detects noise... am I right ?)

I pretend to hook the wireless devices to a serial link, but I refuse to connect the receiver output directly to the MCU because I don't wanna flood the UART with noise and burning processing time to validate each data.

The questions are:

1) Is there any ortodox way to solve it?
2) Any good ideas...?

Thanks

 

[vfone]

The name of the circuit that will do the job is: Squelch
**broken link removed**

 

[Regnum]

vfone,
Thank you for your help, but unfortunately the Rx module has no monitor output for RF level, so It can't control any external circuitry... perhaps the squelch should control itself making the decision based upon the presence of high frequencies at the output... am I right ???
Thanks.

 

[vfone]

The Squelch circuits uses a threshold driven by the audio (or baseband) noise. They are used in FM and Digital Trunked Systems.
Beware that this circuit has some histeresys, which should be taken into account.

 

[Borber]

You may try to invert digital signal on TX and RS side. Idea is that you have max out power on TX when signal is zero.

 

[Dr Strangelove]

I had the same problem with a pair of OOK TX/RX modules from Aurel.

If you are using a cheap OOK RX (superregenerative RX+data slice detector), be sure that supply voltage is clean, because the data slicer of the RX is very sensitive, and sometimes what appears to be RF noise, is symply due to a dirty supply voltage, specially if there is digital circuitry in your board.

 

[Borber]

Superregenerative receivers at 433.92 MHz have sensitivity about -100dBm. They have no squelch, no good selectivity and noise level on output is high.
After demodulation they have high gain baseband amplifier and comparator. Comparator reference is usually set to the same voltage as amplifier (half of the supply voltage) and small noise voltage can trigger it. If you introduce slightly different reference (offset) for comparator you will have some sort of squelch.