I was taking apart an old phone (an old LG GM360). It was always a terrible phone. Anyway, I found one of these inside when I was tearing it down:


I have also found some of these in the back of my current phone (Galaxy S4 - i9505), where there are several of them, I do not think they are antennas, as according to the instruction manual the antenna is at the top right of the device (as you look down at it from the back), and yet these things are not really in that position.

They have holes cut out from them in the case, so only the plastic, black part is visible.

What are these things?

EDIT: It turns out they are antenna connectors.

Is it possible to actually connect a commonly available antenna to them?

What connector would I need for this type?

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    \$\begingroup\$ Antenna connectors. \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 13 '14 at 20:46
  • \$\begingroup\$ I have edited my question with 2 extra mini-questions. \$\endgroup\$ – George Oct 13 '14 at 20:55
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    \$\begingroup\$ "Is it possible to actually connect an antenna to them?" No, they just put them in because they look pretty! \$\endgroup\$ – Majenko Oct 13 '14 at 21:03
  • \$\begingroup\$ Haha, I might need to clarify that slightly! \$\endgroup\$ – George Oct 13 '14 at 21:04
  • \$\begingroup\$ I know olds nokia bricks had them easily accessible and you could buy eXternal car antennas for them. Then technology marches on and antenna tech improved and frequency changes made them obsolete \$\endgroup\$ – Passerby Oct 13 '14 at 21:12

This is some sort of RF test connector with a built-in switch. Possibly an MS-156 or MS-147. There is a trace going under the connector from the bottom, and another one from the top. One side goes to the radio in the phone, the other goes to the antenna. Generally the test connector is installed so that when something is plugged in, the antenna gets disconnected and the external connector is connected to the radio in its place. This allows easy testing of the radio during assembly to ensure that everything works correctly. This is necessary because if the antenna is not bypassed, the whole phone would need to be placed in a faraday cage to isolate it. My phone (a galaxy S3) has three of them under small round stickers.

They're not really designed for use with external antennas, but that doesn't mean it's not possible, just not convenient. Generally they're designed to work with pogo pins in an automated tester, it may be very difficult to find the correct adapter. And then you would need to know what frequencies the radio needs to use, and find an antenna that wil work across those frequencies. Modern smart phones have radios for GPS, Bluetooth, and Wifi in addition to the cell network radios LTE, GSM, Edge, 3G, etc. These radios operate in different bands and in some cases share the same antenna. There may also be complex RF switching to select the correct antenna and/or switch antennas on the fly, complicating the process of properly adding an external antenna. You may need more than one antenna to get everything to work correctly.

From looking at the images of the S4 in ifixit, there is definitely more than one antenna. Samsung does an excellent job integrating everything, though, so they are not very obvious. Looks like there are at least 4 antennas in the back cover - two on the top right, one on the top left, and one at the bottom. You can see two of them after taking the battery cover off; they are under the two small plastic covers on the sides at the top. Then there is another one that curves around the inside of the top right corner. Then there is at least one more down at the bottom with the speaker.

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If I'm not mistaken, that's an 'MS147' RF connector. In its normal state it acts as a pass-through on the PCB and connects the phone's RF stage to the built-in antenna. But when you plug a mating connector in, the pass-through is broken and connects to your external antenna instead (or whatever else is on the end of your cable).

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They are auxiliary antenna connectors for every RF device the designer thought to put one in for. They are often used for testing the boards before the antenna in the plastic back-shell is snapped on. If you know what you are doing, you can use them to build a phone into a metal display and still have reception through external antennae.

Edit1: As I said above: Yes you can use them, IF you know what you are doing, what with impedance, wavelength, antenna design, and such.

They are probably {EDIT2:} NOT {/EDIT2} SMA connectors, though I am not sure.

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  • \$\begingroup\$ Thanks! I have edited my question with 2 extra mini-questions. \$\endgroup\$ – George Oct 13 '14 at 20:54
  • \$\begingroup\$ @George See my update.. \$\endgroup\$ – Asmyldof Oct 13 '14 at 20:56
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    \$\begingroup\$ SMA is a threaded connector, and probably too big to fit into a phone case at all, so I'm pretty sure that's not it. Usually these guys are very low-cost micro-miniature connectors that are only rated for a few 10's of connect/disconnect cycles. I don't know if they're even standardized or if they're proprietary from vendor to vendor. \$\endgroup\$ – The Photon Oct 13 '14 at 21:02
  • \$\begingroup\$ @ThePhoton Fair point. I don't do antenna connectors. \$\endgroup\$ – Asmyldof Oct 13 '14 at 21:03
  • \$\begingroup\$ Another angle - this is the picture of them on the back of the S4. I use my S4 as a camera so I can't take a picture of it myself! Anyway, they are near the DEMO sticker at the top. storage17.gear3rd.com/files/thumbs/2014/05/24/… \$\endgroup\$ – George Oct 13 '14 at 21:19

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