Are there any special considerations for extending a UHF-carrying coax wire in a small device?

Question

In the process of doing a repair on a mobile phone, I've tracked down a "no service" issue to an antenna lead inside the case. Specifically, it has detached from the U.FL/MMCX (I'm not sure which this is) connector soldered to the mainboard.

You can see on the bottom half of the image the white wire is broken off and sitting to the down and to the right of the connector (marked "1") it's intended to be part of. Note that this wire isn't an antenna itself; it carries the signal from the GSM radio on the mainboard to the actual antenna module on the other side of the device. It is intended to be terminated on both sides.

The problem is that the antenna wire has become so frayed, that I don't think there's enough of it left to cleanly resolder to the connector.

So, some new wire is in order. Problem is, I can't find any direct replacements for this device.

What I need to know is, if there are any special considerations for the right gauge and material of wire to use for this embedded UHF antenna use case. Can I grab an arbitrary bit of copper coax of a similar size and splice it in, or does the 1900MHz signal this line will carry demand more precision in the materials or techniques used?

Answer 1

The coax impedance must be matched and the cable must be able to carry the 1900MHz signal. It might say the impedance on the cable (like 50Ω or 75Ω), if it does then your in luck. If it doesn't then the only way to find out is to test it (which would be very difficult and require specialized equipment).

Additionally the repair would need a continuous wire (so no splicing). Splicing can't match impedance specs. The cable would need to be soldered (or connected) in the same way to the antenna as the cable is now.

The easiest thing to do would be to get a new antenna/cable, but whatever happens the impedance must be matched.