433mhz TX kills a previously working RX?

Hey gang,

I have the usual 433mhz arduino compatible pairs like this:

I have previously setup a sender and receiver sketch OK, and seen a serial monitor result for it all working.

Today I try to hook them up in a wider project, and nothing works. Troubleshooting, I realise that if I turn the TX off, the RX is OK again. It starts receiving signal from commercial remotes etc that it could not a moment before.

I plugged the TX back in and tried the remote for my ceiling fan. Like the arduino RX unit, the fan didn't respond - it eventually did return a beep, but 1/10 tries. Again, turning the TX off resolved this.

Both are using the OOTB spring antenna which I know is less than ideal, but I am confused about how the TX could cause such an 'RF storm' that things would not work?

Update:

Of course I tried different distances without success.

I have however moved to one of those 4 channel TX modules with the antenna as a pinout....still then bread boarded it to the same old antenna.

Things seem fine now.

What's that about?

kptb:
but I am confused about how the TX could cause such an 'RF storm' that things would not work?

Sounds normal behavoiur to me.
A nearby TX on the same frequency, or even one on a quite different frequency, can easily overwhelm a receiver that is not that selective, which is often the case with cheap stuff.

"In telecommunications, desensitization (also known as receiver blocking) is a form of electromagnetic interference where a radio receiver is unable to receive a weak radio signal that it might otherwise be able to receive when there is no interference. This is caused by a nearby transmitter with a strong signal on a close frequency, which overloads the receiver and makes it unable to fully receive the desired signal."

kptb:
. . . Troubleshooting, I realise that if I turn the TX off, the RX is OK again. It starts receiving signal from commercial remotes etc that it could not a moment before.

I plugged the TX back in and tried the remote for my ceiling fan. Like the arduino RX unit, the fan didn't respond - it eventually did return a beep, but 1/10 tries. Again, turning the TX off resolved this. . . .

I'm not clear what you mean by "turn the Tx off". These transmitters use on/off keying (OOK) which means they typically have power applied, but are transmitting only when the DATA pin is high. When there is not data being transmitted, the DATA pin should be low or else the transmitter would be emitting a signal, effectively blocking anything else from using that frequency. The usual OOK libraries (e.g. RadioHead) will ensure the DATA pin is low when no data is being transmitted.

The symptoms you describe sound as if the Tx is idling in the on state while you're trying to use a different transmitter device, which is a silly thing to do, for the reasons noted by the previous posters.

MrMark:
I'm not clear what you mean by "turn the Tx off". These transmitters use on/off keying (OOK) which means they typically have power applied, but are transmitting only when the DATA pin is high. When there is not data being transmitted, the DATA pin should be low or else the transmitter would be emitting a signal, effectively blocking anything else from using that frequency. The usual OOK libraries (e.g. RadioHead) will ensure the DATA pin is low when no data is being transmitted.

The symptoms you describe sound as if the Tx is idling in the on state while you're trying to use a different transmitter device, which is a silly thing to do, for the reasons noted by the previous posters.

I think it was a demo sketch with pretty low delay() in the loop.

Thanks guys. What you are saying seems to add up...

But....I swapped it out to another TX unit (one with four channels and an antenna pinout lined up with all the standard pins.

This one didn't block all the other RF units? It was still a relatively cheap aliexpress unit on the same sketch?

Only thing I can think of is the antenna. Rather than the curly spring, I used a dupont wire running from the antenna pin to arduino GND. Didn't measure the dupont to an ideal length or anything like that?

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