12/18/2023 0 Comments Diy cell signal booster![]() I tried microscopes, magnifying glasses, magnifed eyeglasses that you jam into your eye socket - all to no avail. Īfter several weeks of trying to solder the RF amplifier chips I eventually concluded that the techniques that I was using to accurately position the chips was not up to scratch.Another idea would be to upgrade the PCB stack to a better grade of material which would improve parasitic capacitance.Īt 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. ![]() 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. 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. 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. Nonetheless, using this device inside a building improved the upload speeds by a factor of 2x and the download speeds of about 10x. 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. The chip does not seem to obey the laws of surface tension, which usually 'pulls' the chip into position 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 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. Compatibility is determined by the actual BPFs selected as they have different frequency bands for each network. Instead, the duplexer is used to monitor the strength of the cell phone's signal via a 'Received Signal Strength Indicator' (RSSI) chip which can be used to check that network compatible phones are present. The circuit has a VGA for transmitting the cell phone's signal back to the base station but this is not currently used as transmitting noisy or very strong signals to the base station can damage the network. The strong signal transmitted from the cell phone is typically about 1/4 watt when far away from the base station and weaker when close to the station. The BPF filters are 'duplexed' which allows the same antenna to be used for Rx and Tx simultaneously. Since the circuit can pick up some unwanted interference, the signal is now routed into a second identical BPF which then connects to a plate antenna located inside the building. The VGA is capable of adding another 32 dB of gain to the signal and can handle up to 1/2 watt of power with a noise figure of 1.5 dB. This component actually contains two amps cascaded together giving a total possibility of four cascaded amps in the whole Rx part of the circuit. Next in the signal path is the variable gain amplifier (VGA) which is controlled by the Arduino using the SPI bus. ![]() Selecting both LNAs can provide 37.5 dB of gain with a noise figure of just 0.55 dB. The signal then travels through a low loss coaxial cable and is routed into the Rx (791 to 821 MHz for my network) port on the duplex band pass filter (BPF) on the left hand side of the diagram above.įollowing the red arrows in the diagram, the signal is routed into a low noise amplifier (LNA) which can be configured using the Arduino in three possible ways: 'Off', 'One LNA' and 'Both LNAs'. 4G signals generally have good penetrating ability but do not like going around big objects. 'Line of sight' does not mean that we have to actually see the base station, it's more of a theoretical term and really just means 'no major obstacles'. The external antenna is pointed directly towards the base station and needs to have 'line of sight' which means that there are no major obstacles such as large buildings, hills and trees in the way. The 4G signal from the local base station is captured using an external logarithmic Yagi antenna mounted high up on a pole. ![]()
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