A cell phone signal booster is a fully fledged cellular repeater, which receives the RSSI (received strength signal indication) from one or more BTS (base transmitting stations) outdoors and amplifies it indoors. It retransmits this amplified signal via an indoor antenna which radiates (makes available) this signal to a subscriber’s cell phone within this indoors area. This is called indoor coverage. The path the signal has travelled from the BTS to the cell phone is called the downlink or the MS (mobile station) path. This is the transmission that the subscriber hears. The opposite path where the subscriber talks are called the uplink or BTS path. This is when the cell phone signal indoors is amplified by the same repeater and is transmitted back to the BTS which connects the subscriber to the rest of the world.
The same way a microphone will feedback when held too close to a speaker, the same way a repeater will oscillate if not correctly installed or the wrong antenna system and placement are used. Oscillation may not occur at first if your whole household is subscribed to the same network provider. But what happens when a friend comes to visit who is using another service provider who’s signal has been over-amplified by your newly installed repeater? The whole repeater systems go into howling/oscillation. This causes severe problems for other network users and can damage or burn out your repeater. The warranty does not cover damage to the repeater caused by oscillation as it is due to incorrect installation.
If you purchased a repeater over the counter or over the internet and the above happens, who is responsible for the repairs to the repeater? Important question. Will you be able to get hold of the supplier you ordered from via the internet? Make sure your supplier has a fixed “Domicilium citandi et executandi” (a fixed business address), a fixed land line or fax line, and that they are a registered cc or Pty. Ltd. Check whether they are VAT registered. All this should be visible on the quotation. Do you know where to send or deliver your repeater should it need repairing? Does the company actually exist?
The short answer is no. Based on the information given above it is clear that anyone who advises differently is ill informed and you should steer clear of them. In South Africa, where so many formats are being delivered over different frequencies, the cell phone repeater cannot be sold as an over the counter DIY appliance. It is an expensive appliance that requires the correct choice of frequency, the correct antenna system and the correct installation knowledge. Using an app like OpenSignal gives a lot of information, but only at ground level and only for one sim network operator and direction of the BTS can not be properly determined as no directional antenna can be fitted to an Android cell phone. The following RSSI measurements can well be taken before and after amplification.
Accessing Field Test Mode on the iPhone is relatively simple, just open the Phone app, switch to the keypad and dial the following code: *3001#12345#* and then press call. If you dialled it correctly, your iPhone will enter Field Test Mode and you’ll see the numerical value for signal strength in the upper left-hand corner of the screen where the signal strength was previously displayed in bars. To exit and return your iPhone to normal status, all you need to do is hit the Home button. The mode is available on any iPhone running iOS 4.1 and all later versions. If you want your iPhone to always display numerical signal strength instead of signal bars, you can perform the following process. Once in Field-test mode (accessed by entering and dialling the code above), hold down the power button until you see “Slide to Power Off”, then release it. Then hold the Home button until you’re returned to your main app screen. You’ll now see your numerical signal strength while you use your phone, and you’ll be able to tap the signal numbers to switch to signal bars and vice versa. To exit this permanent field-test mode, simply reboot the phone or re-load Field Test Mode and exit it via the Home button.
Accessing Field test mode on Android phones is also straightforward. You simply need to find your way to “Settings” > “About Phone”, and your numerical signal strength will be available under either Network or Status, depending on the model of the phone you own.
Most other phones also support a Field Test Mode. Some more popular phones are listed in the following document: Field Test Modes. You can load OpenSignal or GSM Signal (free apps for Android phones)