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As it is hard to describe, I made a small video showing my issue: https://vimeo.com/521857517

As you will see, the RF transmitter and receiver are correctly connected as they work when I touch a specific part on the transmitter. If anyone could help me understand what is wrong (and how to fix it), I would really appreciate it.

I also tried connecting a 100K resistor to it (with electric tape for now) and to ground and it works as well...

I’m using a 1M resitor on the encoder and a 470K on the decoder... could it be the problem? Thanks

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  • \$\begingroup\$ I see you only touched the metal can lightly, but if you touch the same part with something non-conductive, like a plastic stick, does it work? If so, that might suggest a poor solder joint somewhere. (However, it is more likely that Andy aka is correct.) \$\endgroup\$ – Andrew Morton Mar 10 at 14:41
  • \$\begingroup\$ Something in plastic doesn’t work. I did try with a resistor connected to ground and it seems to work but it wasn’t solder so the test is not 100% accurate \$\endgroup\$ – Dominique Mar 10 at 14:44
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You appear to have not connected the transmit antenna: -

enter image description here

See also this picture: -

enter image description here

Image taken from this page

And, from your video, you clearly don't have a transmit antenna: -

enter image description here

So, when you touch the chip, your body is acting as an antenna.

As you will see, the rf transmitter and receiver are correctly connected as they work when I touch a specific part on the transmitter. If anyone could help me understand what is wrong (and how to fix it), I really will appreciate

You should connect an antenna then they will be correctly connected.

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  • \$\begingroup\$ I did test with an antenna as well without much success. And when the transmitter is place under the wires, I’m not toutching it anymore and it still works... \$\endgroup\$ – Dominique Mar 10 at 14:21
  • \$\begingroup\$ From my reading, the antenna is optionnal and it should work as the receiver is only a couple or inch apart... \$\endgroup\$ – Dominique Mar 10 at 14:21
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    \$\begingroup\$ At a glance I mistook that big coil for an antenna, but it is apparently part of the filter, it sits in series with "R433" which is supposedly a SAW filter. Why they didn't use chip inductors, I have no idea. \$\endgroup\$ – Lundin Mar 10 at 14:32
  • \$\begingroup\$ @Dominique If you don't mount an antenna there you'll get a stub, which in turn might not radiate anything, just cause standing wave issues and muck up the whole impedance matching, assuming this cheap module had any of that to begin with. \$\endgroup\$ – Lundin Mar 10 at 14:36
  • \$\begingroup\$ Could it be that the frequencies of the transmitter and receiver are mismatched far enough that touching the transmitter de-tunes it enough to match the receiver? \$\endgroup\$ – Andrew Morton Mar 10 at 14:43
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I ended up gluing a short piece of metal right here enter image description here (Bottom right corner from top of the right resistor (I think they are resistor) to the bottom of the left one.

Once this was done, I started receiving a strong signal (without antenna). I put a short piece of wire on the transmittor and was able to get a strong signal from one side of the house to the other (no antenna on the receiver).

I have no idea why it works but I’m pretty excited with the result.. I will try with longer antenna on the transmitter and a long one on the receiver as well.. I think I’ll get a very long range!

Thanks all of you for your inputs

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