All Rx Components now Working!

A project log for Cell Phone 4G LTE Repeater / Booster / Femtocell

An outside pole mounted aerial picks up 4G signals which are then filtered, amplified and re-transmitted through a second inside aerial.

capt-flatus-oflahertyCapt. Flatus O'Flaherty ☠ 10/13/2017 at 11:410 Comments

The issues getting all the amp chips to work together has been solved - turns out it was a combination of bad soldering and one tiny trace on the LNA circuit being missing. The previous log showed a board design with small 0.2mm positioning pads -  boards were manufactured with these features and proved to be incredibly effective in getting the chip exactly positioned. The chip does not seem to obey the laws of surface tension, which usually 'pulls' the chip into position

The effectiveness of the design is given by the uploading and downloading speeds of the cell phone and in the last test, with all the components working as they should do, uploading was at 2 Mb/sec and downloading was at 12 Mb/sec with a theoretical maximum of about 7 Mb/sec and 38 Mb/sec, which suggests that there is still some fine tuning to be done at some time in the future. Nonetheless, using this device inside a building improved the upload speeds by a factor of 2x and the download speeds of about 10x.

Just a quick note about 4G speed testing - The cell phone and the network communicate systems data with each other in both directions and the network will transmit actual useful data to the phone in increasing degrees of complexity depending on the signal quality that the phone receives. If the phone detects poor signal quality it will tell the network to give it data in a simplified format which in turn means that download / upload speeds are diminished.

The next step in the project would be to analyse the circuit with a Vector Network Analyser (VNA) to fine tune it and make sure that signal is not reflected back into the Rx antenna on the Rx side of the circuit. Another idea would be to upgrade the PCB stack to a better grade of material which would improve parasitic capacitance.

At some time it would also be nice to be able to get the Tx part of the circuit working but currently I can't test this without my network's permission.