coupling an external antenna

[Asjad]

Dear Friends,

I have been looking on the internet for an external aerial to connect to a
Nokia mobile 3510i.

I have found many possible antennas, but cannot find a way of coupling the aerial to the actual mobile.

Could I simply solder the cable (from external aerial) to the existing mobile aerial?

Any ideas how to overcome this challenge?

Thank you

 

[RadioRon]

Asjad, if you really want to improve the performance by adding the external antenna, you have to make a connection to the phone through a coaxial connector or specialty connector provided on many phones. Often this connection is part of the handsfree cradle kit so you may have to buy a car kit cable that brings out this RF connection. Unfortunately, this can be a bit expensive. These connectors are almost always custom for the particular series of phone, so you won't likely find one in a generic coaxial connector store. They are usually available from cellphone accessory suppliers online or in cellphone stores.

I just had a look around for a car kit for your model phone and none of the ones I found brought out the antenna connection, so I'm wondering if you phone does not provide this option.

If you phone does not have the ability to connect to a car kit external antenna then you may be out of luck. If you try to solder to the existing antenna you may end up with much worse performance than doing nothing because the impedance matching is not only quite critical, but at these high frequencies is very difficult to get right without a network analyzer and some experience in impedance matching networks. There is often a 50 ohm connection point inside the phone but is often buried, difficult to identify, and requires disassembly to get at.

One other option may be to use one of those no-contact couplers used in some car kits. These pick up field directly from the existing cellphone antenna and pipe it to an external coax. My experience with these is that they have to designed for exactly your phone or they won't work worth a darn. Even so, they always suffer a few dB of loss, so your external antenna has to work harder to make up for this.

And one last option is to find the test port available on many phones. The factory uses this port to attach test equipment via coaxial cable to the phone on the production line. These ports are usually inside the phone and you get at them by pulling out a tiny little rubber plug somewhere on the back of the phone or under the battery pack. Unfortunately, the series of coaxial connector used on these ports is not readily available and usually only available from one supplier so even if you find this port, you are not likely to find a connector to plug into it unless you know someone in the cellphone manufacturing or repair business.

Good luck.