What is a so called “Signal Booster”?

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 repeater, therefore, consists of an outdoor antenna (various antenna systems are required for different formats and different gain applications). This is known as the donor antenna. This antenna needs to be positioned at least 8 meters off the ground in a single story building and needs to face the BTS where the RSSI has been measured at it’s best -dB gain. This antenna must not face over the coverage site or be positioned so it may possibly reflect from an adjacent building or structure.
• A cable connects the indoor repeater to the donor antenna. Depending on the signal frequency being amplified (it being GSM900, DSC1800 or WCDMA2100) the length and type of low loss cable will be advised by a qualified installer as attenuation plays a large role with regard to the type of cable used. The type of connector and the way the cable is terminated is critical with regard to the proper operation of the repeater.
• The choice of the repeater is important (it being GSM900, DSC1800 or WCDMA2100). Do not buy a repeater DIY kit and never over the internet because;
  1. as you most probably will buy the wrong model and waste money. See point 3 for more detail.
  2. The network licencing has been issued to the network operators. Besides being illegal, by indiscriminately connecting to it you could very well cause a lot of subscribers loss of signal, dropped calls and a loss of revenue to the network by producing oscillation by incorrect installation.
  3. The choice of the correct repeater should be determined by a qualified installer using the correct measuring equipment. How else will you know what frequency band to amplify and which booster to use to do so?
• Repeaters are available in single and dual band models which are combinations of frequency bands above. What is essential to understand is that the networks are built, maintained and licenced to Network Operators. The network is built and maintained by them and does not belong to the public. Users of the network subscribe to using it and pay according to their usage of voice and data bundles. This is what a sim card makes available. Once we understand this then we can understand that the Network Operator can and does make changes to their own networks as they see fit to serve their subscribers and satisfy their investors in obtaining the best possible Capex. Therefore there are areas in the country where GSM900 is all you would need to make a call and have GPRS access to the internet. Other areas where the population is denser, only dual band repeaters will give you access. 3G is still mostly available in suburban areas only and is run on UMTS on the WCDMA frequency but 3G is now also available is certain rural areas on GSM900. What about 4G or LTE? It should be clear that the repeater you require and what service is available in the sky above your tree line is not a “thumb suck” option. The installer is rigged to measure this and make a proposal to a subscriber.
• A cable from the repeater to an indoor antenna/s completes the RF installation.
• A stable electricity source is required. Load shedding, lightning, unbalanced three phase, heavy machinery or pumps of the same circuit and generators are all hazardous to sensitive appliances such as repeaters. The necessary protection must be installed to prevent this and ensure a proper warranty and backup service can be provided.
• The repeater should be protected on the power supply input by a voltage surge protector. If a 12Vdc repeater is being used and being powered by batteries, solar power, etc, take care to use a voltage stabilising transformer. It allows dc input voltage to fluctuate between 9 and 18Vdc and will ensure a steady 12Vdc to your appliance. Amplitec 12Vdc repeaters are protected by a 12.6Vdc cut-off to avoid oscillation as result of voltage increase. Take note that if a battery is being charged, a 13.8Vdc supply is running over the battery into the repeater. Solar panels can supply up to 16Vdc. The data side (the donor antenna side) should be protected by an inline coaxial lightning gas arrestor. This is placed inline just before the donor antenna cable enters the building. A 1-meter earthing spike is knocked into the ground and the inline coaxial lightning gas arrestor and the earth spike are connected by a good quality and thickness of the copper wire.
• The warranty does not cover damage to the repeater caused by voltage surge or lightning spikes. The voltage surge protector does provide a warranty for the repair of the repeater if a voltage surge protector was used and the warranty applied for and if the data side was protected by a coaxial lightning gas arrestor.
  

  1) Oscillation or feedback

  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.

  2) DIY – Warranty – Repair

  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?

  3) Can I Do a Site Survey Myself?

  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.

  4) iPhone Field Test Mode

  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.

  5) Android Field Test Mode

  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.

  6) Field Test Mode on Other Phones

  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)