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), tea-drinking general secretary 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!

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UK Hams Get New 'Moonlight' Channelssignal strength
Friday 31 October, 2014, 08:00 - Amateur Radio, Spectrum Management
Posted by Administrator
Back in the early days of citizens band (CB) radio in the UK, when the 40 available channels were busy and bustling, some enterprising operators found that by changing the voltages on the pins of some of the integrated circuits inside their CB radios (the PLL), it was possible to make them operate on channels immediately below the normal 40. These channels were only used by those 'in the know' and were illegal to use (then again when did legality ever bother CB operators?) They became known as the 'moonlight' channels referring no-doubt to their somewhat illicit status and the fact that they tended to be busiest late at night.

moonlight channelsMove forward over 30 years and as of today (31 October 2014), radio amateurs in the UK have access to an additional piece of VHF spectrum from 146 to 147 MHz. Access to this extension to the 2 metre band is only through a notice of variation (NoV) which can be applied for by any full licensee on the RSGB web-site. The new spectrum will initially be available for just 12 months though Ofcom may automatically extend this if they see fit and is on a non-interference basis meaning that radio hams must not cause interference to any legitimate users (e.g. in neighbouring countries) and must accept any interference that those users cause.

There are other limitations notably that the maximum transmitter power is 25 Watts, antenna height must not exceed 20 metres and in Scotland (and within 40 km of Scotland) the upper band edge is 146.9375 MHz.

Given the date of the release of this new piece spectrum to radio hams and its uncanny similarity to the original CB band extension (being immediately adjacent to the normal allocation) Wireless Waffle suggests that these new channels be also named the moonlight channels. To celebrate the release of the new VHF moonlight channels, we have compiled a list of one hundred horrible Halloween hits to dampen the spirits at any party.

Anyone for a natter on the newly designated moonlight calling channel of 146.666 MHz tonight?
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Who will pay to re-farm the radio amateurs?signal strength
Wednesday 12 June, 2013, 11:54 - Amateur Radio
Posted by Administrator
military signalsOfcom have just opened a consultation on the use of 2310 to 2450 and 3400 to 3475 MHz spectrum band by radio amateurs. To cut a long story relatively short, the Ministry of Defence who are the current occupants and owners of these bands, have decided to release parts of them for new uses, most likely to be LTE mobile broadband networks. The MoD are releasing the spectrum from:
  • 2350 – 2390 MHz; and
  • 3410 – 3600 MHz.
Ofcom has conducted compatibility tests and determined that it would be unfeasible for radio amateurs to continue to use the bands once LTE networks are in place, as interference would be caused to the LTE base stations. As such, amateurs in the UK are set to lose the vast majority of the 3.4 GHz band, and have a big hole punched in the middle 2.3 GHz band. They are not the first to suffer in this respect and many other countries have, are, or will be releasing spectrum in these bands for commercial usage, thereby heavily restricting amateur use.

change aheadThis would leave UK radio amateurs with a still reasonably healthy allocation at 2.3 GHz comprising 2310 – 2350 and 2390 – 2450 MHz, noting that the frequencies above 2400 MHz are shared with WiFi, Bluetooth and other licence exempt devices. At 3.4 GHz, the situation is much worse as the current allocation of 75 MHz, would be reduced to just 10 MHz from 3400 – 3410 MHz.
The Ofcom consultation document claims that there are only around 200 or so amateurs who are active in these bands and any economist will tell you that upsetting 200 people for the potential benefit of 60 million, no matter how important those 200 people are, is a no-brainer.

But the consultation is not really about the continued use of the bands which are being handed over to commercial users, it’s more about whether radio amateurs should also be allowed to continue using the other parts of the band. The logic seems to go:
  • Once the released chunks of spectrum are given over to new users, any existing use (e.g. MoD, government and programme makers) which was previously in that band, will be concentrated in the remaining pieces of spectrum.
  • Whilst, at present, radio amateurs share nicely with existing users, once everyone is forced into less spectrum the potential for interference is commensurately greater.
  • Further, as radio amateurs can use high power transmitters, they may also cause interference to the commercial users in the adjacent spectrum.
  • As such, it would be easier all round, if the use of the whole of the 2.3 GHz and 3.4 GHz bands, and not just the released bits, were denied to radio amateurs.

radio ham jamGraciously, Ofcom is not proposing such a draconian measure, but is instead suggesting that radio amateurs be given continued access to the remaining portions of the 2.3 and 3.4 GHz bands but with a reduced notice period of 3 months. The plan would be that if users experience interference from amateurs, Ofcom would terminate amateur use in a 3 month timeframe (instead of the more usual 1 year cut off period). This seems like an eminently reasonable and pragmatic proposal.

Activities such as this, where users are forced to give way to others is commonplace in the radio spectrum and has been termed ‘re-farming’ as it is akin to a farmer changing the use of his land. Not long ago, Ofcom undertook a similar activity with radiomicrophone users, forcing them out of channel 69 and into channel 38 in the UHF television band to make way for LTE services at 800 MHz. The key difference here, though, is that Ofcom recognised that there was a cost associated with thousands of radiomicrophone users having to buy new equipment, and set up a scheme to fund the replacement of the equipment. The funds were paid for from the dues generated by the sale of the spectrum.

Moving out of the 2.3 and 3.4 GHz amateur bands will incur costs to many radio amateurs, not least those who operate television repeaters within the affected sections. It seems only fair, therefore, that Ofcom (or the MoD) should support radio amateurs by funding the necessary modifications to this equipment, and making the issue of new licences and frequencies as quick and easy as possible. Given how few users there are, this should not be a costly exercise, compared to the sums that will no doubt be raised when the spectrum is sold to commercial market players.
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Poll: What Should The Radio Spectrum Be Used For?signal strength
Thursday 25 April, 2013, 04:00 - Amateur Radio, Spectrum Management
Posted by Administrator
http   www wirelesswaffle com  keyfob womanOver 5 years ago, Wireless Waffle reported on the fact that a UK radio ham repeater was forced off air to stop interference to licence-exempt 'wireless car unlocking keys' (and no excuses are necessary for re-using the rather fetching graphic one again). In this instance, because radio amateurs are secondary users of the band, and often regarded as second class citizens by regulatory authorities, it was the hams that had to find a solution. The fact that the value of the spectrum used by radio hams is generally rather large, yet they pay little or no licence fees, no doubt increases regulatory lethargy when it comes to lending a hand to deal with these kind of problems.

In the USA, however, the same situation has occurred, but instead of it being radio hams that caused the problem, it was the US military. And instead of it being wireless car keys being interfered with, it was wireless garage door openers. It seems that residents of Savannah (Georgia) have found their wireless garage door openers have stopped operating. The problem is caused by radio base stations at nearby military facilities which have begun operating in the frequency range 380 to 399.9 MHz, which has hitherto been a common band for wireless garage openers.

But unlike in the UK, the US military have stood their ground and said that it's tough luck for anyone who is affected as the spectrum is rightfully theirs. According to US Government Accountability Office report GAO-06-172R:
To address homeland defense needs and comply with government direction that agencies use the electromagnetic spectrum more efficiently, the Department of Defense (DOD) is deploying new Land Mobile Radios to military installations across the country. The new Land Mobile Radios operate in the same frequency range (380 to 399.9 MHz) as many unlicensed low-powered garage door openers, which have operated in this range for years. While DOD has been the authorized user of this spectrum range for several decades, their use of Land Mobile Radios between 380 and 399.9 MHz is relatively new. With DOD's deployment of the new radios and increased use of the 380-399.9 MHz range of spectrum, some users of garage door openers have experienced varying levels of inoperability that has been attributed to interference caused by the new radios. Nevertheless, because garage door openers operate as unlicensed devices, they must accept any interference from authorized spectrum users.

Yay! A big thumbs up for common sense, or at least from a spectrum management perspective that's what it is. But most legal cases use the 'reasonable person' principal. This basically asks the question, 'What would a reasonable person regard as the correct solution?' So... Is it reasonable that the military should be able to use radio spectrum that is rightfully theirs to defend the country, or is it more important to allow people to be able to open their garage doors without getting out of their cars? In this case, the reasonable person (even if that person happened to be the owner of a wireless garage door opener) would probably cede that the military boys have a point.

Now ask the same question for radio hams... Is it reasonable that radio hams should be able to use radio spectrum that is rightfully theirs to talk about radio stuff, or is it more important to allow people to be able to unlock their cars without putting their key into them? The answer in this case is less clear. The reason for this is probably to do with the description of who is using the spectrum for what.

Most people would agree that 'defending the country' was of high value compared to general laziness in door opening practises. But 'talking about radio stuff', well that's a different case altogether. Of course radio hams do use their frequencies for emergency communications and organisations such as Raynet would no doubt argue that use of radio ham frequencies is not about 'talking about radio stuff' but is more about providing a 'national voluntary communications service provided for the community'. If every radio ham was a member of an organisation such as Raynet then perhaps this would hold some water, but listen to your local radio ham repeater (you can check out the GB7OK and GB3OK repeaters online). I'd call that 'talking about radio stuff', wouldn't you?

For a bit of fun, below is a poll. Which of the uses of the spectrum do you value most highly? Just select the ones that you think are the most valuable and click 'submit' and the results so far will be displayed to you.


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