Soldering cable directly on GSM antenna

I have a GSM module that has a very small connector soldered on it. I dont have the cable to connect the antenna to it. I also have a car antenna for mobile phones that has a few feet of 50ohm cable. Can I desolder the connector on the GMS module, cut the antenna cable and solder the antenna cable directly on the PCB of the GSM module. Is there any special way to do it.

Hi,

I'm not really a 'UHF' man, and antenna design/experience is limited.

But I can't see that it will hurt to solder the cable on directly. All a connector really does is 'connect' :) But make sure its a 'good' solder connection, don't want to change the impedence. I can only assume that the connector you are about to remove is 50 ohm. (impedenced matched on the board). Seeing as this is the standard for most GSM modules, and the fact that your cable is 50 ohm, I can't see any problems.

One more thing, I 'vaguely' remember reading a *PDF on PCB design for 900 - 3000Mhz devices, and it had a whole section on 'trace shape'. Basically, I think the cable should be straight, in line with the PCB trace (the one that was for the connector). I'm sure a bit of glue could hold it steady. Avoid 90 degree corners when connecting the cable to the board.

The ground 'shield' wire I imagine could be soldered on any 'GND' trace. Most PCB's nowdays have groudplanes.

Sorry if it doesn't help. Its just what I would do.


BuriedCode.

Do you still have the PDF on antenna design for GSM

Hi techie,

I don't actually 'have' the PDF anymore (searched through my 4GB archive :/) but I think I've found a very similar one, that refer to microwave as opposed to specifically GSM. The design constraints are similar anyway.

http://www.trompeter.com/assets/prod.../may2_reed.pdf

You also might want to look here (for WiFI homemade antenna). It has details of a 'pigtail' something I think you may need.

http://www.binarywolf.com/249/coffee...tenna.htm#null

You 'may' need a MCX -> N-type connector. I've seen a few of these around, see if you can find a place that doesn't charge the earth for something thats probably only worth a can of coke :/

Sorry I couldn't be more use, but my only experinece of UHF (900-2400MHz) design was when I built a 2MB radio link, Using the app notes from microlinear.
If you ask me, a lot of people seem to think that antenna/PCB design for GSM is a 'black art' but the losses in replacing the connector wil be minimal, as long as you match impedence. Try and find the datasheet for your GSM module, it might recommend some antenna designs, and tell you the impedence of the connector.

Good Luck

BuriedCode (listening to 'Panopticon - Isis')