I am sure that you will be aware that offensive or other legally troublesome words can be censored using a bleep. For example if I go on the radio and say I think that “X is a stupid idiot”, then the radiostation can prevent me from making the offensive statement by bleeping the words out.
I would be interested to know if the UK police considered censoring Mr Assange’s speech by using a large fog horn or a similar device. The fog horn was suggested by my legal advisor, while I would go for a very loud rave party or a device from Japan.
I reason that if he chooses to run away from English society and the english legal system then we should consider if he should be free to make a public speech into England. A range of methods exist for jamming things like radio transmissions, as a person (G7LSZ / SA6BID) with years of experience of chasing weak (and not so weak) signals and trying to talk to people in far flung exotic places I know something about jamming.
The most easy system to jam is a conventional FM system, if you can put a unmodulated signal within half the IF pass bandwidth of the receiver at the aerial which is about ten times bigger than the wanted signal then you will make it impossible for the user of the receiver to tune into the wanted signal. This is because of the capture effect which is seen in the series of non linear stages used in a FM receiver.
There are anti-jamming countermeasures which can be taken against this type of jamming, the most common one is to use two aerials and an adjustable delay line and some electronics to cancel the jamming signal. I predict that the best counter-countermeasure for the jammer is to them either use two jammers or to use an aerial array plus some electronics (or maybe just an electromechanical relay) to change the direction from which the jamming signal comes from. I suspect that the Lorenz system which was used in early airport ILS systems could be adapted to give a very good jammer.
AM systems are harder to jam, this is because the signal path in the receiver is more linear, my most simple suggestion for radio jamming of conventional speech signals is to introduce a strong unmodulated signal about 1 kHz from the carrier of the original signal. This will have several effects on the receiver. It will reduce the gain of the receiver by acting on the automatic gain control (AGC) which is a vital part of an AM system, also it will generate a whistle noise when it beats with the carrier. An AM modulated jamming signal is properly better for several reasons.
1. People like me if we were strongly motivated to tune in to a AM broadcast which was being jammed with a simple carrier would be likely to turn off the household radio and start to use a communications grade radio such as a FT-450 or a FT-1000 which has a good notch filter which operates at an IF, or if you were using a cheaper communications grade radio you might flip from AM to SSB and then use which ever sideband which was cleaner.
2. The mixture of random babble which the soviet jammers used would have been more distracting to a person trying to tune into VoA than just a blank tone.
But the frequency hoping and spread spectrum things like GPS are very difficult to jam as these systems constantly change the carrier frequency in a pseudo random manner, unless you have real time access to the algorithm used to tell the transmitter and the receiver to follow each other then it is impossible for the jamming transmitter to follow the signal you are trying to jam. If you widen the jamming signal by changing from something like a signal modulated with an audio tone to something wide like fast scan TV then you tend to reduce the spectral power density. Unless your target is equally wide as your jamming signal then it is unlikely that you will be able have any jamming effect.
But there is a final option which I have inadvertently caused, I was once running 100 watts into a 19 element Yagi array (circa 4000 W ERP) at the G8EYC club at Imperial College, I was beaming south east towards France in the sincere hope of getting a VHF signal over the channel (I did not manage to work France that day, I did it much later running a much lower power as a PhD student from Beacon Hill near Loughborough using a 25 W ERP). I moved to the upper end of the 145 MHz band, and one person spoke to me and told me nicely that I was desensing his receiver. What I had done was to put a strong signal within a few MHz into his front end. This drove it into a non linear state where the RF stage was becoming saturated, as a result the gain for all signals was being reduced.
I think for audio jamming I always thought that the most effective way is to either use the AGC in the human ear to blot out the wanted signal, this in the case of Assange could be done using a fog horn or to exploit a nonlinear effect in the human ear. This has been done for years as a method of drowning out unwanted yelling by playing loud music.
But some people in Japan have come up with something even better, this is the audio version of motorboating. In radio equipment a self inflicted EMC problem is often known as motor boating as it commonly makes a sound like a motorboat engine running at low revs.
If the RF equipment is unstable when attached to a RF load such as a 47 ohm resistor then it is a defect such as a parasitic oscillation which has developed into a real demon oscillation. This fault suggests that a RF stage is unstable, the way to cure this can be to improve the input / output isolation and/or neutralise the stage. Or add some damping to the stage, my late friend Don always wanted to use passive grid circuits for 4X150 power VHF amps this has the advantage that it is very stable while I have always used active grid which is far less damped.
Motorboating only occurs when RF is emitted from a device which re-enters the system and then disturbs it, these effects tend to be worse as the power level increases. I have experienced once in my youth, I had a 27 MHz rig which has poor filtering on the power lead (someone had disconnected a decoupling capacitor). Here the RF which was entering the rig via the power lead was causing the rig to increase this own RF power output, this caused the RF output of the rig to rise until something happened which caused the RF output to drop catastrophically. This caused the RF power to drop greatly, and the increase would start again. It was not doing any harm to the radio it was just an annoyance, and I noticed that if the power was turned down that the effect occurred more slowly.
A five minute job with a soldering iron soon cured the problem, all I did was to reattach the ceramic capacitor.
This invention from Japan works by delivering a person’s voice back to their ears with a short delay, this disturbs the processes in the brain required for forming speech. So as this feedback loop uses a person’s own transmitter (voice) to cause a transmitter defect I think it should be considered as being a phenomena in the same class as motorboating. If I am right to consider it a form of motorboating then the louder a person trys to speak the stronger the effect will be, which will please anyone who is looking for the “smart bomb” of jamming for audio systems. In common with motorboating it does can work without causing any harm to the system which is troubled by it.
I would like to know what my readers think of the idea of censoring Assange with a machine which robs him of the ability to talk while it is pointed at him.