Wireless Waffle - A whole spectrum of radio related rubbish
Martian radio amateurs appeal spectrum allocation decisionsignal strength
Thursday 22 January, 2015, 10:48 - Amateur Radio, Broadcasting, Licensed, Radio Randomness, Spectrum Management
Posted by Administrator
Radio amateurs with designs on operating from the planet Mars are appealing against a decision by the Consultative Committee for Space Data Systems (CCSDS) to allocate the 70 cm amateur band (430 - 440 MHz +/-) for communications between satellites in orbit around the red planet and the numerous rovers that criss-cross its surface.

In a statement, released by the Mars United People for Planetary and Earth Transmissions (MUPPETs), Arthur Dent said,
MUPPETs have been planning a DX-pedition to Mars for some time. To discover that our officially allocated radio frequencies are already in use is just not fair. It constrains our ability to talk about radio stuff to each other and means other radio amateurs around the solar-system will be denied extra points in the forthcoming 'talking about radio stuff with other radio nuts' contest.

Responding to the accusations, Prostetnic Vogon Jeltz of the CCSDS commented,
prostetnic jeltzThe 70cm frequency band has been used for communications on and off Mars since the Viking lander first set foot on the planet back in 1976. The MUPPETs have had plenty of time to comment. The plans for frequency use on Mars have been available at the local planning office on Alpha Century for fifty of your Earth years, so they've had plenty of time to lodge any formal complaints and it's far too late to start making a fuss about it now. I'm sorry but if they can't be bothered to take an interest in local affairs that's their own regard.

Appallingly obvious references to the Hitch-Hikers Guide to the Galaxy aside, it may surprise many people to learn that there is, indeed, a frequency plan for Mars. And that there are already 5 communication satellites in orbit around the planet! For communication from the rovers on the surface to the orbiting satellites, frequencies in the range 390 to 405 MHz are used. For the link down from the orbiters to the rovers, the frequency range 435 - 450 MHz is used, which falls inside the amateur radio 70cm band.

The choice of the particular frequencies in use (on Mars) is designed to try and stop anyone deliberately causing interference from the Earth, whilst retaining ease of use on Mars (i.e. the ability to use omni-directional antennas). The various satellites orbiting Mars typically get no nearer than around 400 km from the surface and communication with rovers typically takes place when the satellites make their closest pass. The shortest distance between the Earth and Mars is typically around 60 million km. The table below shows the path-loss at 415 MHz of these distances.

Route Distance Path Loss
Satellite to Mars surface 400 km 137 dB
Earth to Mars 60,000,000 km 240 dB

So the difference in path loss is just over 100 dB. For a transmitter to cause interference from the Earth to communication on Mars, it would therefore have to have a radiated transmitter power 100 dB higher than the signals passing between the rovers and the satellites.

mars uhfA very good description of the communications with Mars is provided by Steven Gordon (from whom the diagram on the left is shamelessly plagiarised). The transmitter power used on Mars is 5 Watts (7 dBW), so in order to cause interference from Earth, a transmitter power of around 107 dBW, or 50,000,000,000 Watts (a.k.a. 50 GigaWatts) would be required. Would it be possible to generate such a signal?

Firstly, it ought to be possible to generate at least 100,000 Watts (100 kiloWatts or 50 dBW) of power at the necessary frequencies as television transmitters for the UHF band that reach this level are available. So what is then required is an antenna with a gain of 57 dB. This requires a dish with a diameter of around 150 metres. The largest dish antenna in the world is the radio telescope at Arecibo, Puerto Rico, which is 305 metres in diameter.

muppets cq dxIf a high powered television transmitter was therefore connected up to the Arecibo radio telescope antenna, it ought to be more than possible to jam the transmissions between the Mars rovers and the orbiting satellites during periods where the Earth and Mars were closely aligned. Of course this kind of power level is way beyond the normal licensing conditions of a typical radio amateur and the right conditions would occur roughly every 2 to 3 years when the Earth and Mars come closer together. Nonetheless, commenting on this finding, Arthur Dent of the MUPPETs jeered,
Safe from interference, eh? Who looks silly now then Jeltz!

add comment ( 15 views )   |  0 trackbacks   |  permalink   |   ( 3 / 20 )

Ofcom proposes closure of stable doorsignal strength
Monday 19 January, 2015, 16:25 - Radio Randomness, Spectrum Management
Posted by Administrator
comtrend pltOn several past occasions, dating back to 2008, Wireless Waffle has reported on how several users of the short wave spectrum including radio amateurs, broadcasters, air traffic controllers and NATO, have raised concerns about interference caused by power-line telecommunications (PLT) devices (such as the Comtrend unit pictured on the right). PLT devices allow the use of home electrical wiring to carry computer data by injecting radio signals over the wires. As electrical wiring is designed to carry signals with a frequency of 50 Hz and not 5 MHz, the injected radio signals have a tendency to leak out everywhere and cause radio interference over a wide area.

Groups such as UKQRM and Ban PLT have long campaigned that PLT devices (also known as Power Line Adapters) should be taken off the market as they do not comply with the relevant emissions standards.

Over all of this period, the UK spectrum regulator Ofcom, has staunchly refused to accept that these devices contravene any regulations, though they have taken action in a number of cases where the interference they cause has exceeded even their expectations. Over the same timeframe, a number of other devices have also been found to cause high levels of radio interference, particularly cheap electrical devices, often imported on the grey market from China. These include things such as laptop power supplies, LED lighting and solar panel electrical controllers. Yet Ofcom continued to refuse to accept that anything needed doing.

It is therefore somewhat of a bolt from the blue that on January 15th, Ofcom released a consultation document, entitled 'Notice of proposals to make The Wireless Telegraphy (Control of Interference from Apparatus) Regulations 2015' in which it wishes to implement new controls over these devices by making it a criminal offence to operate them if they are causing interference to wireless telegraphy (e.g. radio services). Part of this seems to be driven by the fact that Ofcom were unable to deal with many interference complaints under existing regulations and that this could be regarded as a potential safety-of-life threat where the interference was caused to, for example, aeronautical services.

According to the consultation paper, there were 114 cases of interference reported in 2014, 'where undue interference was caused ... and capable of resolution'. Of those 114 cases, only 3 could be cured quickly using existing legislation and in the other cases it required voluntary action by the user of the equipment to bring about a solution. Under the proposed changes, all of these cases could be dealt with by law, meaning that instead of volunteering to fix the problem, users could be prosecuted if they didn't.

devil slop 2The big question has to be whether such a change would make any difference. Would those selling the devices stop doing so? Presumably not, as there is no law against selling them, just using them. Would they warn buyers of the new law? Not if it damaged sales. And what will happen if Ofcom threaten prosecution to someone who believes they have been using equipment quite legally, having purchased it legitimately, and having seen the various markings on the box that said it complied with the necessary standards? Will Ofcom then look silly for allowing such devices to have been sold in the first place? Sadly, the UK legislation on such things is still somewhat muddy. It is possible to sell, for example, FM transmitters, mobile signal boosters and even GPS jammers. It is just not legal to plug them in and use them.

ofcom horse boltingBan PLT are recommending that as many people as possible respond to the consultation, encouraging the changes to be implemented. No doubt organisations which manufacture or sell the devices will be arguing against the changes and so it is important that those who use the radio spectrum, especially the short wave spectrum, respond to show the strength of feeling.

There is an old saying in England, 'closing the barn door after the horse has bolted'. Effectively it means trying to solve a problem, after it has happened. The new powers proposed by Ofcom may have some effect in allowing Ofcom to convince users to turn off whichever device it is that is causing the problem, but it is by no means certain that the threat of 'turn it off or we will sue' is going to win anyone any friends, Ofcom, suppliers, BT and radio listeners alike.
add comment ( 25 views )   |  0 trackbacks   |  permalink   |   ( 2.9 / 26 )

Hotel Wi-Fi in the spotlight againsignal strength
Wednesday 14 January, 2015, 12:52 - Spectrum Management
Posted by Administrator
Back in October of last year, Wireless Waffle reported that Marriott hotels had been fined by the FCC for deliberately interfereing with Wi-Fi networks in an attempt to try and force guests at their hotels to use the hotel's own extortionately priced WiFi service.

hotel girl laptopEarlier this month, the New York Times reported that several hotel chains have petitioned the FCC for permission to legally undertake such activities. The lengthy petition argues on several points that hotel operators (and other landlords) should be able to manage their networks to the extent that they can identify, and neutralise, anyone trying to offer WiFi services other than themselves, thereby maintaining a quality of service and level of security and safety for their users.

The main tenets of their argumentation seem to be:
  • That the type of sophisticated monitoring and enforcement activities they are proposing do not constitute harmful interference but are good network management practices;
  • That their networks are established using best industry practices to maximuse performance and that non-approved WiFi hotspots mess about with this and degrade their service;
  • That the Part 15 rules that allow users to establish WiFi hotspots require those users to be located on a property where the user has "direct or indirect ownership or leasehold" and that this does not apply to hotel guests.

It then goes on to liken a university applying bandwidth caps to student usage as being a similar network management practice, but one that no-one would argue with and therefore, by implication, the practice of neutralising the threat of miscreant networks should also just be considered best practice.

hotel wifi logoNotwithstanding any of the above, WiFi networks, whether operating under the Part 15 rules in the USA, or in most other countries are permitted access to the radio spectrum on a 'non interference' basis. This means that they are not permitted to interfere with any other users, and that they must accept any interference caused by any other users. In effect, they have no protection from interference at all. What the hotels are trying to do is run a commercial grade wireless internet service in this spectrum. If this were possible, and it were possible to provide the quality of service that users would seek, would it not follow that the big commercial operators would want to do the same thing too. Free WiFi hotspots in a coffee shop is one thing, but trying to provide a guaranteed service is another.

tp link wr702nThe hotel chains argue that when they enter into an agreement to provide services for, for example, a conference, they agree to some quality of service parameters for their WiFi service. This is their own silly fault! It's like guaranteeing your guests that it won't rain this week. It's not something that the hotel has control over. Not least, the WiFi bands are used by a myriad of other, non-WiFi devices, that could equally upset the performance of the hotel's WiFi networks including their very own microwave ovens!

One has to question whether these hotels would be so keen to conduct such complex network management if they offered their WiFi service for free. Hotel visitors should vote with their feet and choose hotels that do offer Free WiFi. Marriott and its friends would soon change their tune, not least as it appears that cheaper hotels have the best WiFi! Oh, and don't forget to take your Wireless Nano Router to set up your own network nice and easily too!

Post Script: It seems that just a day after writing this, the BBC report that Marriott has backed down. Was it something we said...?
add comment ( 34 views )   |  0 trackbacks   |  permalink   |   ( 2.9 / 29 )

Japan's digital spew-oversignal strength
Tuesday 30 December, 2014, 12:48 - Licensed
Posted by Administrator
Japan. Country of Shinto serenity. Where cherry blossom floats down from tree-strewn parks during Hanami. Where tourists come to enjoy peaceful views of Mount Fuji.

Japan. Country of high-technology. Inventors of the pocket calculator, walkman, compact disc player and PlayStation. The first country to launch 3G mobile services.

Japan. Country of very weird pop videos. Where headless pink maids shimmy and where young girls spew out shadowy birds and multi-coloured eyeballs.

So what has all this got to do with anything radio-related. Well, if you can bear to watch it for that long before your brain turns to blancmange (or alternatively just fast forward to the relevant point), you will find in the video of PonPonPon by Kyary Pamyu Pamyu at approximately 2 minutes 30 seconds in (just after the eyeball spewing incident), a video cassette going into a TV, a TV mast growing and the screen of the TV turning snowy. This, believe it or not, is a tribute to the closure of analogue television in Japan.


Kyary Pamyu Pamyu - PONPONPON on Vimeo

Most countries have celebrated the closure of analogue television with announcements ranging from the upbeat to the sombre, montages of classic TV programmes, countdowns to zero hour, or even just snow replacing the picture mid-programme. As there are still a wide range of countries yet to complete the transition to digital TV (most of Africa, South America and Asia), Wireless Waffle challenges those countries (or their pop stars) to come up with an even weirder tribute than that of Ms Pamyu Pamyu!
add comment ( 8 views )   |  0 trackbacks   |  permalink   |   ( 2.9 / 85 )


| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | Next> Last>>