Wireless Waffle has reported many times on the issue of jamming. Jamming, put simply, is the transmission of one radio signal in such a way as to intentionally block another one from being received. It is the intentional nature of jamming that distinguishes it from other kinds of radio interference.

Usually jamming is used for the purposes of disrupting something that the person doing the jamming does not wish to be received. Recently the BBC's satellite services have been jammed by both Syria and Iran who do not want the BBC's version of the news to reach their citizens. To this end, jammning is also illegal, as any kind of intentional radio interference usually is.

There are instances where jamming is sanctioned. In jails in some countries, for example, jammers which block cellular frequencies are used to stop inmates from using mobile phones to communicate to the outside world. Cellular jammers are also used in some mosques to ensure that peace and quiet is not disrupted by the 'Grande Valse'. It is believed that some theatres and cinemas also use cellular jammers to stop mobile phones spoiling the show. Unless explicit authority is gained fromt the regulator of the country concerned, though, the use of jammers, even where the purpose may seem harmless remains illegal. The illegality of jamming means that it is not usually advertised by those doing it.

So step forward chocolate bar Kit Kat who has established 'no WiFi' benches in the Dutch capital Amsterdam. At these benches WiFi is jammed with the idea being that you can go and sit on them and disconnect from the hecticities of daily life and 'have a break, have a Kit Kat'. An interesting question therefore arises as to whether the activities of Kit Kat are illegal or not. Whilst jamming per se is normally illegal, the bands in which WiFi operates (both 2.4 and 5 GHz) are licensed for many more services than just WiFi. In the 2.4 GHz band, for example, it is also legal to operate wireless video cameras, bluetooth, microwave ovens, cordless phones, remote control toys, and many more devices. Some of these devices would have the potential to knock-out WiFi links. CCTV cameras, for example, transmit a continuous signal which would do a good job of jamming WiFi and other services that were nearby.

It would therefore be possible (and legal) to run a number of wireless cameras, on adjacent frequencies such that the whole 2.4 GHz band was jammed. Around 4 wireless cameras would be needed to do this. Now disconnect the camera and just put the transmitter in place and this remains legal (as it is the transmitter which is regulated, not the content). Lo and behold, it would be legally possible to jam all WiFi signals in a limited location. Whilst this is legal from an equipment perspective, whether or not doing this for the purpose of jamming WiFi rather than for transmitting video pictures opens up another legal issue. Article 15 of the ITU radio regulations says:

All stations are forbidden to carry out unnecessary transmissions, or the transmission of superfluous signals, or the transmission of false or misleading signals, or the transmission of signals without identification

Signals that were there for the purpose of stopping other signals being received would surely be 'superfluous'. In addition, article 45 of the ITU radio regulations states:

All stations, whatever their purpose, must be established and operated in such a manner as not to cause harmful interference to the radio services or communications of other Member States or of recognized operating agencies, or of other duly authorized operating agencies which carry on a radio service, and which operate in accordance with the provisions of the Radio Regulations

So if the purpose of running the wireless cameras was specifically to jam WiFi signals, and assuming that those WiFi signals were operating in accordance with the provision of the ITU Radio Regulations, they would remain illegal.

Whether the Kit Kat 'WiFi free' areas are legal or not is therefore a subject that is, perhaps, open for discussion. Whether they are a good idea is equally subject to debate. Whether or not Kit Kat's are the right chocolate bar to have with a cup of tea (or coffee) during tea-breaks is, though, surely not a question that requires much debate. After all, they can't be all bad, if Cheryl Cole recommends them, right?ENXCZZRPWCTV

Following the recent Wireless Waffle post about Wes's excellent Soldery Song, it has been noted that the terms 'C-Band' and 'Ku-Band' were thrown around casually, as if everyone understands what these mean. For the benefit of those who don't, here's a short description of what they're all about:

• C-Band (in satellite terms) refers to frequencies in the range of roughly 4 to 8 GHz. C-Band satellites are commonplace in areas where there is very heavy rainfall (eg tropical areas) as, using relatively low microwave frequencies, signals propagate better and suffer fewer rain fades. It's not the total amount of rain that matters, it's the voracity of the downpours.
• Ku-Band refers to frequencies roughly in the range of 10 to 15 GHz (the 'roughly' refering to the fact that uplinks and downlinks work in different bands that may or may not be within this range but are at least somewhere nearby). Ku-Band is the band most commonly used for digital satellite television broadcasting anywhere that it doesn't rain too heavily (eg most non-tropical areas). In many areas, the geostationary arc is near saturation in Ku-Band, with satellites positioned every 2 degrees or so. Some satellite operators have tried to launch broadband internet services in this band but the high levels of congestion make it difficult to find the space to do so.
• Ka-Band refers to frequencies roughly in the range of 20 to 30 GHz. Ka-Band is the relative newcomer on the block (though Italsat F1 conducted some tests in this band in the early 1990s). With Ku-Band becoming congested with broadcasting, satellite operators wishing to offer broadband services are increasingly turning to Ka-Band to do so and it is fast becoming the most hotly contested band for new satellite services. Already popular in the US, it is now being successfully commercialised in Europe and Africa. In emerging countries, where terrestrial (including wireless) broadband services are unlikely to be rolled-out any time soon, the use of Ka-Band satellite broadband is likely to open up Internet access to millions of people who wouldn't otherwise have a hope of getting a decent connection.

It is perhaps no surprise that in the battle to gain access to Ka-Band, some of those doing the fighting are going to lose out. This seems to have happened to Australian satellite company NewSat. Recently both Morgan Stanley and Lazard have pulled out of the programme raising funds for the launch of NewSat's Jabiru 1 satellite. Digging into the economics of NewSat, it appears that the numbers just don't add up. The cost of their capacity would be around 50% higher than that of existing Ka-Band satellite operators, which might be a difficult sell when trying to raise lots of capital to build and launch a new satellite.

From the figures on their web-site, NewSat were going to pay Lockheed Martin US$550 million to build and launch their 'bird'. The resulting satellite would operate in a total of around 8.4 GHz of Ka-Band spectrum. Compare that to UK satellite company Avanti who paid US$400 million for their bird, but which accesses 11 GHz worth of Ka-Band spectrum. Do the maths and you see that NewSat would be paying approximately US$66 million to access each GHz of spectrum, whereas Avanti paid only US$36 million. This difference in cost is borne out in prices too, with NewSat claiming to be aiming to charge customers US$1.3 million for a transponder for 12 months. The equivalent price for Avanti is around US$0.9 million.

This may not yet be a Ka-tastrophe (groan) or even a Ka-lamity (double groan) for NewSat. NewSat suspended trading in its shares in November to give it time to re-think it's financing strategy. Maybe there is still a 'hope in heaven' for those communities that NewSat was intending to serve, if, of course, the other satellite operators don't get there first!

Wireless Waffle received an e-mail from Des of Ireland. Des writes:

Since early May I have been noticing many many frequencies being occupied by very short bursts of digital 'noise' which are random in their frequency and time but very recognisable. So far pattern emerged is that they follow an 8 kHz spacing right across the HF bands (from 3.4 MHz to 28.5 MHz), but mainly in 6 to 9 MHz region. Even 6622kHz Shanwick being clobbered ... These noise bursts in the HF bands intrigue me, I wondered if it is a basic military comms set-up in case satellites/internet/microwave/fible-cable are clobbered.

Take a look a the picture below (click on it to open a much larger version). It is a snapshot of the radio spectrum between roughly 6550 and 6950 kHz taken using the University of Twente's on-line receiver in the Netherlands (which is a marvel in itself). The snapshot was taken at about 07:00 GMT. The horizontal axis shows the frequency, the vertical axis is time (in thie case about a minute). Straight vertical lines represent constant transmissions. Dotted ones (such as the broken line just above 6600 kHz) are morse code. Other squiggles that are roughly vertical are all manner of other signals that can be found on the HF bands.



What is of interest here are the horizontal dashes of which there are three at the top left hand corner (just under 6550 kHz), four just below 6950 kHz and various others scattered across the chart, seemingly randomly (see around 6665 kHz and 6555 kHz for two bright ones). These are not bugs in the University's software, nor are they local interference in Twente. What they are are bursts of data from a frequency hopping transmitter. If you tune into one of the frequencies just at the time when the transmission is taking place on that frequency, you will hear a 'chuff' noise which is the quick burst of data that is being sent. If you happen across a frequency that has multiple 'hops' on it, the effect is not totally unlike there being a steam train on the frequency (listen to this actual recording).

At HF, this hopping transmission is almost certainly military in nature. Frequency hopping at HF is not at all uncommon. Even back in the 1980s, Racal's TRA 931XH would happily hop around the HF bands. In the case of the '931XH it did this by changing frequency roughly every second. Transmissions were just SSB (with an initial data burst to synchronise the receiver and transmitter - this is essential so that the two follow the same sequence of frequencies). The Wireless Waffle team had the fun of seeing a demo of the '931XH which was set to hop from frequencies between around 6950 and 7450 kHz, right across the 41m broadcast band. The effect of the hopping was to change the background noise every second or so - sometimes with a loud whistle caused by the carriers of the broadcast signals. The effect to anyone who happened to listen on a frequency that was being used would have been that they would have heard speech for a second which would then disappear.

There's nothing unusual about the use of frequency hopping transmitters. Your bluetooth headset does this, and most GSM networks are set up to use frequency hopping too. The reason for using frequency hopping can be many and various, such as:

• Hopping around makes the transmission much more difficult to detect. Unless you know the sequence of frequencies being used, it's almost impossible to follow the transmission from one frequency to the next.
• Hopping can overcome some kinds of interference. If one frequency is blocked (from a broadcast transmission for example) the information sent on that frequency is lost, but if most are clear of interference, the error correction schemes can be arranged to deal with missing blocks and the overall communication is unaffected.
• Hopping can help overcome fading and propagation problems. In a GSM network for example, Rayleigh fading will cause some channels to have deep fades and others not. Hopping around makes sure that these 'dead' channels do not cause a total lack of communication.

It's not surprising then that the military are using hopping on the HF bands (nor anywhere else for that matter). The question that remains unanswered is whether the military still need HF given all their other channels of communication. Patently they do!

About 18 months ago, the Wireless Waffle team wrote a paper on the topic of what radio amateurs in the UK might have to pay if spectrum pricing was applied to the spectrum they use. The paper was offered to the RSGB and to Practical Wireless as material that could be used for an article in their prestigious magazines.

The RSGB indicated that it was not the sort of article they normally published as it didn't have antennas in it or any pictures of people standing on a mountain or remote desert island. Practical Wireless never responded as they were too busy assessing the merits of the latest amateur radio gizmo to come from Latin America (see right) and the whole thing got shoved to the bottom of the 'to do' pile and forgotten about. At least I think that was what the RSGB and PW said, the old memory is a bit hazy on the subject.

Whilst the material contained in the paper is now around a year old, it still makes for interesting reading and it is almost certain that Wireless Waffle readers will find it worth the time to study. Rather than think what to do with it next, it has been uploaded to the web-site and is now available for anyone to download and read.

So, for your reading pleasure, we present 'The Duffer's Guide to Spectrum Pricing. Pour yourself a beer, turn on your VHF radio, and have a read. Then, if you are a radio ham, realise how lucky you are to be able to afford that beer you just poured yourself!