Sunday, March 31, 2019

Simple 4G LTE signal booster / amplifier that finally works

The components are purchased cheaply and yet the circuit is also very simple. This is my first prototype 4G LTE indoor signal booster that I am currently building to solve the slow internet connection that I've experience for so long.

In the past 9 years streamyx internet connection has been doing unfair capped bandwidth at 2 Mbps and yet the reality performing only around 0.5 Mbps ~ 1 Mbps and the connection keeps on turning on and off. Then I go for DiGi 4G LTE 100 GB internet package that comes with the HuaWei WiFi mobile modem - it's doing alright with signal strength around 1 to 2 bar performing at 3 Mbps and below. I guess anyone out there using Digi Internet experiencing almost the same day in day out. I am pretty sure of that unless your house is located next to the Cell Tower station.

Based on the android signal software analysis the DiGi could actually provide up to 72 Mbps super fast connection but that's probably if the device is placed right on the cell tower microwave antenna which is not going to happen. In reality we will get around 1 Mbps ~ 3 Mbps and sometimes 5 Mbps depending on the proximity between the device (mobile phone) to the cell tower distance. That speed usually linger around -107 dBm to -101 dBm which is below average. This happens usually when you are inside the house.

Signal Strength Analysis based on LTE discovery android software:

-107 dBm to -101 dBm = 1 Bar
-99 dBm to -90 dBm = 2 Bar
- 89 dBm to 80 dBm = 3 Bar
- 70 dBm and below full bar

Which means the higher the negative value the weaker is the signal strength otherwise the lower the negative value is the stronger the signal strength.

Having said all that I've made quite sometimes of research to build antenna amplifier / booster for the HuaWei modem to get better signal that it is currently receiving. And here comes the final prototype running on 20 Mhz crystal to modulate the weaker signal into 20 Mhz output.

The following are the components:

20 Mhz Crystal Oscillators
Coupled Inductor 20 mH
Air core inductor 2.5 Turns
2 x Input antennas (to harvest signal from surrounding environment)
1 x Output signal to transmit / broadcast the signal to the HuaWei modem

Despite the circuit output only 20 Mhz but there is quite significant impact of it to the HuaWei Modem signal - as you can see in the video demonstration it could amplify up to 4 bars signal which increase the internet speed within 9 Mbps to 15 Mbps range. And the signal strength is very consistent as oppose to without the amplifier circuit.

NOTE: When signal is very weak within your area - the modem signal strength sensitivity becomes very high which means a slight movement and placement (angle) of the modem could effect the signal strength significantly. That's why if you found a good spot and position where the signal is very strong take note of it because the rest of other positions / placement could be very bad. In this circuit do not place the transmitting antenna too close to the modem because the signal output will over powered the modem input signal. Placing too far is also not good because the signal cannot reach the modem. In my case i purchased special made 4G LTE antenna with two coil on the antenna and placed it within 7 cm away from the modem. This is the best distance that i have experimented. I believe different antenna could possibly emitting different signal strength - so self experimentation is required how far it is from the modem.

To ensure your circuit works - test using a multimeter with the Hertz mode. The crystal should transmit / oscillate around 8 Mhz ~ 12 Mhz at the output and the ground of the crystal should generate around 2 Mhz ~ 4 Mhz. If anything lower than this it could affect the signal strength - please experiment at your own discretion. Connect only the output connection to the output antenna and do not connect the ground because it will provide a constant frequency 20 Mhz. A constant frequency is not good and you must allow it to oscillate to emit the RF signal.

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