We recently had a customer who lives in a remote country location and had bought a directional antenna for his mobile broadband modem. He connected the modem and antenna and then spent an entire day pointing the antenna in different directions in the hope that he would see his signal strength go from the intermittent one signal bar he was getting to something better. Unfortunately his efforts were in vain and he ended up contacting us for help.
After about 30 minutes we had got a stable internet connection that showed as three bars on the modem's connection manager software………So how did we do it?
High gain directional antennas can really help improve a 3G \ 4G performance, but keep the following in mind
1) If you are unable to get any signal without an antenna then the chances are an antenna isn’t going to help because the signal is just too weak or non-existent.
2) We often hear of customers buying extremely high gain antennas with the belief that the higher the gain the more ‘powerful’ the antenna. This is not necessarily true and most people will find that a medium gain (10 dBi) directional antenna is the best option.
There were several reasons that our customer failed to get his directional antenna working:
1) He had no idea where the nearest cell tower was for the mobile broadband operator
2) He was using the connection manager software to indicate the signal strength
3) He was making large adjustments every time he re-pointed the antenna
4) He was using 4 * 2 meter USB extension cables to get the modem in the roof of his office so it reached the antenna.
Locating the cell tower
Directional antenna’s are just that ‘directional’ and they must be pointed accurately towards the cell tower otherwise they won’t work.
To find the location of the nearest cell tower we used a website called sitefinder http://www.sitefinder.ofcom.org.uk/ run by the UK telecoms regulator OFCOM. The website shows the exact location on a map of every mobile network cell tower and some basic information, such as network type (i.e. 4G, 3G, 2G etc), tower height, power output.
Getting accurate signal strength information
Most connection managers that come with wireless modems have bars indicating the signal strength. The problem is that they are not very accurate and there is a delay between each refresh which makes it very hard to work out at which point the antenna was getting a good signal.
One method of getting accurate signal strength information is to use to use Hyper Terminal to connect directly to the modem and use AT commands. Entering the command AT+CSQ will bring back a result showing two numbers separated by a comma e.g. 16,99. The first number is called the received signal strength indicator (RSSI) and represents the signal strength. Check the RSSI number against the table below to determine the signal strength.
0 < -113 dBm (Poor)
1 -111 dBm (Poor)
2 -109 dBm (Poor)
3 -107 dBm (Poor)
4 -105 dBm (Poor)
5 -103 dBm (Poor)
6 -101 dBm (Poor)
7 -99 dBm (Poor)
8 -97 dBm (Poor)
9 -95 dBm (Poor)
10 -93 dBm (OK)
11 -91 dBm (OK)
12 -89 dBm (OK)
13 -87 dBm (OK)
14 -85 dBm (OK)
15 -83 dBm (Good)
16 -81 dBm (Good)
17 -79 dBm (Good)
18 -77 dBm (Good)
19 -75 dBm (Good)
20 -73 dBm (Excellent)
21 -71 dBm (Excellent)
22 -69 dBm (Excellent)
23 -67 dBm (Excellent)
24 -65 dBm (Excellent)
25 -63 dBm (Excellent)
26 -61 dBm (Excellent)
27 -59 dBm (Excellent)
28 -57 dBm (Excellent)
29 -55 dBm (Excellent)
30 -53 dBm (Excellent)
31 > -51 dBm (Excellent)
Positioning the antenna
By moving the antenna many inches at a time our customer was effectively adjusting the location of where the antenna was pointing by several miles in the distance.
Always make very slow, small adjustments (one centimetre at a time) of the antenna and continually check the signal strength by entering AT+CSQ into Hyper terminal and checking if the signal has improved.
It’s also worth noting that the adjustments should not just be horizontal, but also vertical.
Connecting many USB extension cables to increase the length causes additional noise that means any additional gain from having an antenna is effectively lost.
Get one long USB cable rather than using USB extension cables. The maximum length of a USB able should be kept to 5 meters, any longer and there will be significant degradation in the signal.
It is better to get a longer high quality antenna cable than use longer USB cables.
Author: Robert Cutts
Please comment below with any tips or software utilities that can help position a directional antenna.