Following Zuma\u2019s speech, Minister in the Presidency Jeff Radebe told journalists he did\u00a0not know who jammed the cellular signals, and said he wasn\u2019t even sure if there was jamming to begin with.<\/p>\n
He added that the secretary of Parliament, after being instructed to investigate the matter, said that whatever was scrambled had been unscrambled.<\/p>\n
![\"Device](\"http:\/\/mybroadband.co.za\/news\/wp-content\/uploads\/2015\/02\/Device-resembling-a-high-power-signal-jammer-discovered-in-Parliament.jpg\")
<\/a>Device resembling a high power signal jammer discovered in Parliament, photo by PowerFM<\/a><\/p><\/div>\n Cellular signals are typically robust, but in general all a jammer needs to do is cause enough errors in the messages received by either the cellphone or the tower to overwhelm their ability to correct them.<\/p>\n Though jamming wireless signals can be done in a number of different ways, there is one general approach that works in just about all cases: add noise.<\/p>\n This type of jamming is sometimes called \u201cdenial of service\u201d (DOS).<\/p>\n Other jamming techniques may target the specific workings of the technology it is trying to disrupt, but if you can generate a garbage signal of sufficient power at the correct frequencies, you have a jammer.<\/p>\n The frequencies and standard (Global System for Mobile Communications, or GSM) used by South Africa\u2019s mobile network operators is well documented, so jamming signals\u00a0isn\u2019t difficult.<\/p>\n All of South Africa\u2019s mobile operators use some combination of frequencies in the 900MHz, 1,800MHz, and 2,100MHz bands.<\/p>\n A jammer that targets the frequencies in those bands could then effectively block almost all the voice and data services on all of South Africa\u2019s mobile networks.<\/p>\n Telkom\u2019s Long Term Evolution (LTE) network is the exception as it runs at 2,300MHz. However, only a handful of mobile phones currently support the technology Telkom uses for its LTE and LTE-Advanced networks.<\/p>\n There is also nothing stopping a jammer from simply targeting 2,300MHz as well.<\/p>\n The next thing someone jamming a wireless signal needs to know is the type of modulation used.<\/p>\n Modulation is the way in which information is encoded into the wireless signal, and for GSM this is a technique known as Gaussian Minimum-shift Keying.<\/p>\n With this knowledge, someone who wishes to jam mobile signals can build a device that outputs another signal at the right frequencies and at a high enough power.<\/p>\n The infographic below details how signal jamming works.<\/p>\n How cellphone signal jamming works<\/p><\/div>\n South Africa\u2019s telecommunications regulator, the Independent Communications Authority of South Africa, has previously said that using jammers is illegal<\/a>.<\/p>\n In its findings on \u201cmobile telephone blocking devices\u201d published in a Government Gazette during 2002, Icasa said it would not license jammers for use in South Africa.<\/p>\n \u201cThere appears to be no legitimate radio communications use for cellular jamming devices,\u201d the gazette stated. \u201cIcasa has therefore decided that use of jamming devices will not be authorised\u201d.<\/p>\n Therefore, whether used privately or publicly, \u201cno organisation is allowed to jam cellular signals, and any device which is used to jam signals is illegal\u201d.<\/p>\n Alleged cellphone signal jamming at Zuma speech<\/strong><\/a><\/p>\n Cellphone jamming illegal: ICASA<\/strong><\/a><\/p>\n Jamming devices worth R200,000 recovered<\/strong><\/a><\/p>\n Criminals using jammers to access your car: police warning<\/strong><\/a><\/p>\nJamming a wireless signal<\/h3>\n
![\"How](\"http:\/\/mybroadband.co.za\/news\/wp-content\/uploads\/2015\/02\/How-cellphone-signal-jamming-works.jpg\")
<\/a>Using jammers illegal \u2014\u00a0Icasa<\/h3>\n
More articles on wireless jamming<\/h3>\n