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everybody.

I have an already working ZWave radio on my PCB. It has a PCB antenna and it's working perfectly. I need to add the Si4362 Low Current Receiver which is a receiver for the bands from 142 to 1050 MHz to my device.

Due to constraints in the PCB size and the fact that modifications to the enclosure are pretty much impossible at this stage of the project, I need to examine the possibility of sharing the PCB antenna between the ZWave transceiver IC and the Si4362 Receiver-only IC.

I took a look to the question Sharing antenna between receiver and transmitter but it deals with the fact that they are separate receiver and transmitter both for 433 MHz and the answer states that the antenna could be connected directly to both wich I don't think applies to my use case.

Also in the question Shared antenna on multiple 2.4Ghz receivers the answer suggest a power divider or splitter, but I don't need to just split the signal. I need to be able to switch between the two radios to decide at run time wich radio will use the antenna. Fortunately, both don't need to be active at the same time.

Also, I can't use chip antennas because ZWave doesn't allow that.

Does anybody know how to achieve this?

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  • \$\begingroup\$ Perhaps an antenna switch? Or a diplexer if they both operate on different frequencies. Or a directional coupler so outbound signals go one way and incoming signals go another way. \$\endgroup\$ – Sam Nov 28 '16 at 21:31
  • \$\begingroup\$ @Sam that makes sense, but, what kind of switch? how do I connect it? Where can I find an application example or information about how to do this properly? Because I've seen that there are Absorptive and Reflectible. \$\endgroup\$ – m4l490n Nov 28 '16 at 22:01
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    \$\begingroup\$ Checkout Digikey, I use it more for finding components than I do for buying them, digikey.com/product-search/en/rf-if-and-rfid/rf-switches/…. Absorbative switches are more expensive because they have built-in termination resistors and are most useful if you have to switch between sources that are always on (hence the need for proper terminations). Reflective switches are fine for switching most receivers and can be used for switching transmitters too provided that you power down the RF amp BEFORE switching the output over to another device, you might cook the amp otherwise. \$\endgroup\$ – Sam Nov 29 '16 at 20:41
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RF Switch with PIN diodes

This switch is based on a design from an article I wrote about diodes. The 50 Ohm resistor makes the switch absorptive for the transceiver, so that it doesn't short the output. The receiver can be shorted with a reflective switch. This will improve the isolation, which will help keep power from the transmitter from overloading the receiver too much.

PIN diodes make good RF switches. They have low on-resistance and low off-capacitance, and are usually lower cost than IC RF switches. The inductors need to be high-impedance at the signal frequencies. They need to be high-impedance at the frequencies of interest. The 2.2uH chokes in this schematic are not optimized for your application. If you can tolerate a little bit of loss, a 1K or 2K resistor is a lower-cost and easier-to-design substitute for the choke.

More details are in The PIN Diode Circuit Designer's Handbook from Microsemi.

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  • \$\begingroup\$ Thanks!, it seems that this si exactly what I need. The only problem is that I don't have a drive circuit that can swing to both positive and negative voltages. So I need to check out this a bit more in depth to see how can I adapt it for my needs. \$\endgroup\$ – m4l490n Dec 1 '16 at 19:14

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