1. I want to solder a u.fl connector to the xbee. I removed the rp sma connector to reduce weight. Will soldering a U.FL manually cause impedance mismatch?

2. Should I solder a co-ax directly to this antenna? Or remove the central conductor and solder an rp-sma central conductor in the antenna?

 

Welcome to AAC.

Connectors are convenient but parasitic. They should have a characteristic impedance that matches the transmission line, but they will always cause insertion loss, however small. If you properly solder the coax directly, you will have the correct impedance and less loss.

If you don’t need a connector, you will be better off directly connected—all other things being equal. Since there are many factors involved, empirical testing is certainly appropriate, but there in nothing inherently wrong with the idea.

 

I don't have any means of testing the impedance. That's why I was thinking of removing antenna central conductor and soldering an rp sma connector central conductor

 

Welcome to AAC.

Connectors are convenient but parasitic. They should have a characteristic impedance that matches the transmission line, but they will always cause insertion loss, however small. If you properly solder the coax directly, you will have the correct impedance and less loss.

If you don’t need a connector, you will be better off directly connected—all other things being equal. Since there are many factors involved, empirical testing is certainly appropriate, but there in nothing inherently wrong with the idea.

I don't have any means of testing the impedance. That's why I was thinking of removing antenna central conductor and soldering an rp sma connector central conductor

 

I don't have any means of testing the impedance. That's why I was thinking of removing antenna central conductor and soldering an rp sma connector central conductor

Testing would be by checking the transmit strength and the receive sensitivity compared to the connectorized version. You would most easily to this using the RSSI function. If you place two modules at a relatively long but fixed distance apart and make the changes to one of them, you will see if performance is degraded or improved—or the same.

 

Will a different connector cause an impedance mismatch? Almost certainly.
Will it have a detrimental affect? Probably not. The RF chips are incredibly tolerate of impedance mismatches, in that they will not blow up with a mismatch.
If you're looking for the longest transmission range, then matching impedances is important to get the most power down the antenna. But for garden variety type projects, the range is not such an issue.