A crash course for FM radio jamming for our engineers in Pakistan Army and ISI...

Jamming: a primer

Tuesday, February 17, 2009 Chris Cork Much has been talked but little actually done in the matter of jamming the so-called "Mullah Radio" that has done much to inflame the situation in Swat. The government appears to take the position that this is an immensely complex and expensive task, requires vast resources and the import of foreign equipment – most of which is not necessarily the case. Few will have little idea of what "jamming" actually entails – or even what it is. Radio jamming is the generally deliberate transmission of radio signals that disrupt communications or the radio channel by increasing the signal-to-noise ratio; which is defined as the ratio of a signal power to the noise power corrupting the signal. Signals can be unintentionally jammed or interfered with by another broadcaster transmitting on the same frequency without first checking that the channel is in use; alternatively, the signal can be disrupted by the switching on of something like a cable TV plant. The plant radiates a signal which, for instance, could interfere with the emergency frequency used by aircraft. None of this is "new knowledge" and has been around almost as long as radio itself. (Marconi is generally credited with the invention of radio in the last years of the 19th century and the early years of the 20th.) Intentional communications jamming is usually aimed at an adversary's radio signals to disrupt control of their equipment and communication/information systems during a battle. A transmitter, tuned to the same frequency as the opponent's receiving equipment, and with the same type of modulation, can, with enough power, override any signal at the receiver. There is a range of ways in which this can be done. The most common types of this form of signal jamming are random noise (sometimes called "white" noise), random pulse, stepped tones, warbler, tone, rotary, pulse, spark, recorded sounds, gulls (as in the sound of the common seagull, which is a disconcerting "squawk") and sweep-through. These are all forms of noise designed to overlay broadcast and render it unintelligible, and they can be divided into two groups – obvious and subtle. Obvious jamming is easy to detect because it can be heard on the receiving equipment. It usually is some type of noise such as stepped tones (bagpipes, for instance, an instrument played in Scotland with a penetrating "drone"), random-keyed code, pulses, music (often distorted), erratically warbling tones, highly distorted speech, random noise (hiss or "white noise") and recorded sounds. Various combinations of these methods may be used, often accompanied by a regular Morse-code identification signal to enable individual transmitters to be identified in order to assess their effectiveness. For example, China, which has used jamming extensively, and still does, plays a loop of traditional Chinese music while it is jamming channels. The purpose of this type of jamming is to block the reception of transmitted signals and to cause a nuisance to the receiving operator. Subtle jamming is jamming during which no sound is heard on the receiving equipment. The radio does not receive incoming signals, yet everything seems superficially normal to the operator. These are often technical attacks on modern equipment, such as "squelch capture." Thanks to the FM capture effect, Frequency Modulated broadcasts may be jammed, unnoticed, by a simple unmodulated carrier – something that would present little or no difficulty to the communications wing of our armed forces were they to be directed to locate and interdict transmissions from "Mullah Radio." (Location will not be a problem either – simple signal triangulation will suffice.) Screwing up the oppositions comms (radio-geek-speak for "communications") has been something in the military manifest for many years. During World War II ground radio operators would attempt to mislead pilots by false instructions in their own language, in what was more precisely a "spoofing attack" than jamming. Jamming of foreign radio broadcast stations has also often been used in wartime (and during periods of tense international relations) to prevent or deter citizens from listening to broadcasts from enemy countries. However, such jamming is usually of limited effectiveness because the affected stations usually change frequencies, put on additional frequencies and/or increase transmission power. A more sophisticated form of jamming is used to limit access to the Internet by totalitarian regimes – China and Saudi Arabia, for example, both of which severely limit Net access. Pakistan has the capacity to do this also, but it has been used infrequently. Netizens are usually able to find a way around Net jamming by using proxy servers. Jihadi groups make extensive use of the Internet to propagate their message. The increased use of Net-based comms systems like Messenger and Skype present other challenges to the jammer; with Skype giving particular difficulties as it uses an encryption system whose key it refuses to release. In occupied Europe during WW2 the Nazis attempted to jam broadcasts to the continent from the BBC and other allied stations. Post-war and into the Cold War Soviet jamming of some Western broadcasters led to a "power race" in which broadcasters and jammers alike repeatedly increased their transmission power, utilised highly directional antennas and added extra frequencies to the already heavily overcrowded shortwave bands, to such an extent that many broadcasters not directly targeted by the jammers (including pro-Soviet stations) suffered from the rising levels of noise and interference. Radio Free Europe and its sister service Radio Liberty were the main target of Soviet jammers, followed by Voice of America and the BBC World Service. The BBC World Service is still jammed in China from time-to-time. Against this background of nigh-on a century of interruptive activity of radio signals, both shortwave and FM, we may be able to see that our own inability to shut down or disrupt Mullah Radio is not a failure of technology on our part, nor is it something beyond our technological reach. Indeed, were we to be really serious about shutting down Mullah Radio it would be a simple matter at field-level to locate the signal source and then vector an appropriately armed aircraft and blow the thing – and its operators – to kingdom-come. It is doubtful that the operators are yet so sophisticated that they can auto-shift frequencies to confuse any jammer, their on-air timings are not difficult to determine and the equipment they use is not so portable as to be something they can backpack from location to location. Simply put, they are the proverbial sitting ducks. The failure is not military or technological – it is political. It is a failure that stretches far back into the Musharraf years and is probably linked to the fallacious notion of "strategic depth" that still in part informs military and political thinking. Today we are seeing a shift in the political winds as the new American crew breezes through our part of the world. President Zardari has spoken clearly and forcefully in the last few days of the threat presented to us by the Taliban. Their power and reach are both extended and consolidated by the use of radio and other media, and the State has been either absent, slow or simply negligent in terms of understanding the threat presented by Mullah-radio. We can and should switch off their mouthpiece. Jamming would be the humane way of accomplishing that – starting tomorrow. (The News) The writer is a British social worker settled in Pakistan. Email: manticore73@gmail.com