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I have a cellphone mainboard from a Sony Z Ultra:

enter image description here

There are 4 antenna connectors on the board, 3 of them unconnected (marked with red dots). One of them is connected (green wire), that might be the GPS antenna.

The big blue rectangle is the headphone jack connector, and my intention is to find if any of those antenna connectors (red dots) can be used for adding an external antenna for the FM tuner.

(I know that FM tuner usually uses the headphone jack as antenna - but I'd prefer using a small connector if possible)

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    \$\begingroup\$ Those connectors are for GPS, WiFi, Bluetooth, Cellular -- none of them are connected to the FM radio input pad on the radio chip. If you don't want to plug in a headphone, you could use this antenna (amazon.com/ENUODA-3-5mm-Radio-Antenna-Mobile/dp/B0185KMVOO) designed to plug into the headphone jack. Or just solder a wire into a headphone plug (shell contact) and you're there. \$\endgroup\$ Nov 1, 2020 at 23:31
  • \$\begingroup\$ The problem is that I put this board into a frame and there is not too much space there for any connector in the jack socket. But yepp, I can solder the FM antenna onto the connector of the headphone socket :) If we are already here, can you tell me which connector is for the GPS? \$\endgroup\$
    – Daniel
    Nov 2, 2020 at 8:25
  • \$\begingroup\$ You could look at the antennas that were removed to determine that, but if those are gone, search YouTube for a teardown video for this phone. \$\endgroup\$ Nov 2, 2020 at 16:44
  • \$\begingroup\$ You might convert your first comment to answer, and I'll accept that. Thank you! \$\endgroup\$
    – Daniel
    Nov 3, 2020 at 16:08

1 Answer 1

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Those connectors are for GPS, WiFi, Bluetooth, Cellular -- none of them are connected to the FM radio input pad on the radio chip. If you don't want to plug in a headphone, you could use this antenna which is designed to plug into the headphone jack. Or solder a wire into a headphone plug (use the shell contact) and you're there. If there's no room to insert a headphone plug, just solder a 75 cm (or 2 ft) long wire to the shell contact of the headphone socket on the PCB.

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  • \$\begingroup\$ Please confirm me one thing: "shell contact" means the GND of the headphone? I.e.: robrobinette.com/images/Audio/TRS_Pinout.jpg "sleeve" here? \$\endgroup\$
    – Daniel
    Nov 8, 2020 at 17:57
  • \$\begingroup\$ Yes, 'shell' and 'sleeve' are basically the same thing. But there is a nuance -- smartphone audio jacks follow a CTIA standard, that places the microphone signal on the sleeve, and the ground is on the ring adjacent to the sleeve. So I'd try that ground contact first for your antenna wire. \$\endgroup\$ Nov 8, 2020 at 19:41
  • \$\begingroup\$ Yes, this phone actually follows the OMTP standard, as if I connect a wire to the sleeve, it helps increasing FM signal, but if I connect the same wire to the adjacent one, it does nothing. Thanks! \$\endgroup\$
    – Daniel
    Nov 8, 2020 at 20:33
  • \$\begingroup\$ One more thing: I wanted to connect a car antenna into this socket and it has a ground wire too. Any idea where shall I connect the grounding of the car antenna? As I already connected the signal to the jack's "ground", I ran out of ideas. \$\endgroup\$
    – Daniel
    Nov 8, 2020 at 21:42
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    \$\begingroup\$ Other jacks (such as USB) should have shells connected to the PCB ground. Or look for any internal shields, or the negative battery terminal. Trace these back to find the PCB ground. That's where you would connect the ground of the car antenna. \$\endgroup\$ Nov 8, 2020 at 22:08

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