Jamming - a technical response to a political problem.
This page is devoted to demonstrating the negative effects of jamming on the free flow of information and spectrum management.
Jamming or intentional interference is the act of broadcasting noises or programming on the same frequency as a signal that an administration does not want its citizens to hear.
The best way to describe jamming is to hear examples of it. Below you will find a selection of jamming types used against various international broadcast language services. The samples are in RealAudio(RA) format.
BBG programs in the following languages are currently jammed. Click on the hypertext links [in blue] to hear sound samples.
VOA and RFA Mandarin Chinese broadcasts suffer from at least 2 different kinds of jamming.
Co-channeling sounds like a harmless case of mutual interference. If it weren't for the fact that the Radio Beijing programs move with us every time we change frequencies, we might even believe that ourselves!
This sample of co-channeling of VOA's Chinese broadcast is taken from Shanghai on January 7, 2001 at 0934utc on 15515kHz.
Growler jamming is probably the most effective form of jamming used by the Chinese. It is produced by superimposing a heavily overmodulated signal on top or near our frequency. The result is almost unlistenable.
This sample of 'growler' jamming of RFA's Mandarin broadcast is taken from Beijing on January 5, 2001 at 0304utc on 17495kHz.
VOA and RFA Tibetan
VOA and RFA Tibetan progams have been jammed since their inception - 10 years ago for VOA and 5 years ago for RFA. The jamming level has increased during the past 12 month and is quite effective, as the following 2 samples demonstrate.
The first sample is an example of a 'warbling growler' jammer used against VOA Tibetan on January 7, 2001 at 0012utc on 7200kHz as heard in Kathmandu, Nepal.
The second sample shows co-channeling of RFA's Tibetan also on January 7, 2001 at 1108utc on 7470kHz as heard in Kathmandu.
VOA and RFA Korean
We first learned that North Korea was jamming VOA's Korean language programs several years ago when someone from Radio Japan's Korean service advised us. The jamming was inaudible on our Seoul RMS; probably 'skipping over' such a close location. Even today we can only hear the jamming reliably from our Kobe, Japan RMS.
RFA Korean was jammed within days of its appearence in 1996.
This sample of RFA's Korean broadcast is from January 5, 2001 at 2238utc on 9455kHz as heard in Kobe, Japan.
The same frequency just a few minutes later on the same date sounded like this in Seoul.
RFA Vietnamese
Radio Free Asia (RFA) Vietnamese language programs began February 6, 1997. They have been heavily jammed since the first day of broadcast. As new frequencies are brought on the air, jamming signals appear.
The jamming consists of Voice of Vietnam 'home service' programming and a 'hetrodyne' or tone produced by the jammer being a few hundred Hertz off-frequency.
This sample is from January 4, 2001 at 0009utc on 11580kHz as heard in Phnom Penh, Cambodia.
Radio Marti
Radio Marti has been jammed by Cuba since it first aired on 1180 kHz from Marathon, Florida over a decade ago. Shortwave transmissions were not jammed for over a year after they started, but are now heavily jammed on all 4 simultaneous frequencies on the air 24 hours/day.
This sample is from January 5, 2001 at 0008utc on 13820kHz as heard in Bonaire, Netherlands Antilles.