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Cell-Phone: How is the external antenna connected to LNA?

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harkonnen

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Hi,

Some Cell-Phones (N0kia for example) have a connector on the back side of the cell-phone that can be used for an external antenna in a car for example.

But I am wondering, how is the RF diverted from the Power-AMP/LNA to the connector? If you connect a 50OHM line to the connector, your internal antenna is still connected. And external and internal antenna are then in parallel and thus not 50OHM.

I can't imagine that they use a SOI-Silicon or PHEMT switch inside since that needs extra board space and is expensive.

So, how do they match both the antennas with the external one connected and disconnected without having significant losses?
 

As I know,the connector is also a test port ,and it is fixed between the PA and the internal antenna.So they are in serial,not in parallel.
 

I just checked the connection in the schematic for a Nokia 6150. There is a mechanical switch in the phone to switch between internal and external antenna. When you put the external antenna plug in the socket you activate the switch. You doesn't activate the switch just by connecting a resistor. You have to put in a plug that matches the socket to activate the switch. If you put in a resistor whithout activating the switch, the internal antenna will not be disconnected and the resistor and internal antenna will be connected in parallel.
 

ME,

Having some kind of mechanical switch seems to make sense.
So, when I plug in a connector then some kind of lever switches from internal to external antenna? Or is it just an electronic controlled relais?
What do you mean by putting a resistor into the socket?

Where can I find the schematics for the Nokia 6150?

Thanks!
 

You can find the manual if you click at the "Manuals" link in the upper right corner of this forum.
The switch is mechanical activated when you push the plug in. There is no kind of relay but pure mechanis whitout any kind of electronics.
 

On the cell phones I've seen, its a mechanical single pole, double throw switch that is part of the antenna connector. It switches when you plug in the external antenna.
 

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