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I am designing a prototype PCB for a Lora node.

It will have an SMA connector (J2) and a PCB antenna.

Switching RF connectors are not available in my area, so as an amateur enthusiast what is a good way to separate the antennas?

I have placed a solder jumper (JP1) before the PCB antenna as seen in the image below. Would it suffice or should I place another one before the sma connector too? Are there other, better alternatives?

enter image description here

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  • \$\begingroup\$ It's kind of questionable to use solder jumpers IMO, as you can't really guarantee 50 ohm impedance. You should also avoid stubs on the part which isn't used, like when that SMA isn't mounted. I'd probably recommend using an antenna switch instead, unless you can do some clever layout changes like placing the SMA "in series" with the on-board antenna. \$\endgroup\$
    – Lundin
    Apr 27, 2021 at 8:33
  • \$\begingroup\$ I am unable to find such switches in my country. I saw some Esp32 designs use 0 ohm resistors. Is it not the same as using a solder jumper? I might fit them into to board in series, but I'd prefer it this way. \$\endgroup\$
    – krypt
    Apr 27, 2021 at 8:49
  • \$\begingroup\$ 0 ohm resistors are more reliable since there's no manual soldering (which can create small antennas in worst case). The important part is no stubs. Also, if you can't buy integrated circuits in your country, then you can't do electrical engineering in your country... \$\endgroup\$
    – Lundin
    Apr 27, 2021 at 9:09

1 Answer 1

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They usually put a 3-pad solder jump.

The central pad is connected to the LORA integratated circuit.

The left pad is connected to your SMA connector.

The right pad is connected to the printed antenna.


Look at this example:

3-PAD jumper


Please note that your antenna is not a patch antenna.

It's just a PCB printed antenna where the PCB works as a mechanical support.

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  • \$\begingroup\$ Oops my bad calling it patch antenna. Thank you! \$\endgroup\$
    – krypt
    Apr 27, 2021 at 7:37
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    \$\begingroup\$ After a couple of days of reading I opted to use a 100pf capacitor to select for antenna. It seems to be a better solution since the frequency is 868 Mhz. \$\endgroup\$
    – krypt
    Apr 30, 2021 at 11:47

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