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I am trying to connect three nodes(A,B,C) through RF cables in the following manner : A can communicate with both B and C(and vice versa), but B and C cannot communicate directly.

Somebody suggested using a splitter for this work, but when I tested one I found that all three nodes could communicate with each other. Now, somebody is telling me to use a coupler. Can a coupler achieve what I want? What is the difference between splitter and coupler?

PS: I am working in the 2.4GHz band(wifi), if that makes a difference.

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  • \$\begingroup\$ A diagram would help. \$\endgroup\$ – Leon Heller May 9 '11 at 13:46
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A splitter definitely won't work. It's a device that accepts an input signal and delivers multiple output signals.

I think that you need a directional coupler. It has an input, an output, a coupled port, and a load. It's a device that operates on an input so that two output signals are available, on the output port (larger signal) and the coupled port (smaller signal). However, when the input is applied to the opposite port of a terminated coupler, only one output signal is produced. MCL makes suitable devices.

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  • \$\begingroup\$ Passive splitter are reciprocal, so they can work in an application like this, you just need to be aware of the isolation. \$\endgroup\$ – Peter Green Nov 2 '18 at 20:33
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Perhaps something like this circuit might help? As drawn, it provides 300:1 attenuation between the first two or last two cables, or 90,000:1 attenuation between the first and the third. Some experimentation may be required to find out how much attenuation is sufficient to prevent the first and last devices from communicating with each other, without preventing the middle device from communicating with each of them. Click each switch to make it send out a pulse and watch the response. Note that the impedance matching isn't quite perfect, but would likely be good enough for most applications.

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It seems the term "coupler" is usually used for an asymetric splitter that provides low loss on the main line while providing a highly attenuated monitoring port. I don't think that is what you are looking for.

Most splitters provide some degree of "isolation" but this isolation is limited, maybe 30dB or so at best (for a high quality splitter with perfect termination). Even a slight impedance mismatch on the common port will lead to dramatically reduced isolation.

What you need to do is put attenutators in the lines to B and C to weaken the signals enough that they cannot communicate directly.

You may also find that you need to put your devices inside well-screened boxes. PCB traces can easilly act as antennas.

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