Wireless Waffle - A whole spectrum of radio related rubbish
How Not To Install A Satellite Dish (Part I)signal strength
Wednesday 1 April, 2015, 04:51 - Radio Randomness, Satellites, Much Ado About Nothing
Posted by Administrator
It's been a long while since anyone at Wireless Waffle installed any satellite dishes, however as part of a project to improve language skills, it was decided that the WW HQ would be fitted with the kit needed to receive German television. This is the sad story of the trials and tribulations of what should have been a simple job in the hope that it may help others trying the same thing not to fall into the same traps that befell our attempts!

Firstly, a visit to Lyngsat and a browse through the dozens of satellites that cover Europe quickly yielded the fact that the channels that were wanted could be found on various Astra 1 satellites at an orbital position of 19.2 degrees East (19.2E). As a ready reckoner, the following orbital positions are the 'hot-slots' for various European languages:
  • English - 28.2E
  • French - 5W
  • German - 19.2E
  • Italian - 5W or 13E
  • Polish - 13E

astra 1m footprintThe next thing to do is find out what size of dish is needed to receive the satellite that's of interest. This is more complex as it requires a knowledge of the satellite's footprint and the strength of signal at a particular location. For 19.2E in the UK, even a 55cm dish should be fine pretty much everywhere, so a Triax 54cm dish was duly purchased together with a suitable wall bracket and an Inverto LNB.

The mounting of the dish on the wall was relatively straightforward, having made sure that there were no obstructions in the line-of-sight from the dish to the satellite (such as trees or other buildings). With the dish on the wall, the next step is to align it so that it is pointing at the satellite. In general a rough idea of the right direction can be gathered if you know your latitude and longitude and the satellite you wish to receive through many online tools (such as dishpointer.com).

Getting the dish pointing in roughly the right direction is not too difficult, but even a small dish needs to be pointing with an accuracy of better than plus or minus 1 degree (bigger dishes have to be even more accurately aligned) and so some form of fine tuning is needed.

In analogue days gone past, by far the best way to align a dish was to connect it to a satellite receiver, and connect the satellite receiver to a television, and put the whole lot in a place where the TV could be seen from the dish. With the satellite receiver tuned to a channel on the appropriate satellite, it was then just a matter of moving the dish about until a signal could be seen on the TV. Once the signal was found, gently moving the dish from side-to-side and up-and-down to a point where the quality of the picture was maximised was all that was needed. Of course the same method can still be used today, but there has to be a less crude way, right? Right...

slx satfinderThe SLX Satellite Finder costs less than a few metres of CT-100 coax, and provides both a visual indication of signal strength (using the in-built meter) and an audible indication (using the in-built buzzer). All that is then required to use this to align a dish is a 'patch lead' so that the dish can be connected to a socket on the meter and then a lead coming from the (indoor) satellite receiver connected to the other socket on the meter to supply power. So far, so good.

Now, turn on the satellite receiver and return to the dish. In theory, the meter should only register a signal if the dish is pointing at a satellite. However, the modern Inverto LNB was obviously doing a far better job of receiving than the systems that the crusty SLX meter was being designed to work with resulting in a full-scale meter deflection (and an annoying beep that could not be turned off) almost regardless of the position of the dish. No amount of experimentation yielded anything other than full-strength or nothing, and the full-strength indication happened across a wide arc of the sky and with the elevation angle of the dish anything within 10 degrees of that which should have been right. In a word, beeping useless!

sf 95dr satfinderNot to be defeated, and rather than cart the TV and receiver outdoors, a second, seemingly more modern meter was purchased, the SF-95DR Satellite Finder. This proved to be marginally better, but having the dish within 'a few' degrees of the right position still yielded a full-scale signal. At least the beep could be turned off.

An old trick from the analogue days to reduce the signal to make fine tuning the position of the dish easier if the signal was very strong, was to cover the dish in a damp tea-towel. The water in the towel will attenuate the signal making the signal weaker and thus the dish easier to align. This trick was tried using the SF-95DR but alas, only resulted in the need to keep picking up a damp tea-towel from the floor, every time the wind blew it off.

Eventually, more through luck than skill, a point was found where the meter indicated a peak that was within a degree or so of nothingness in nearby directions, suggesting that the dish was aligned to a satellite. An excited scan of the receiver revealed some signals but alas, from the wrong satellite (13 East instead of 19.2 East). Of course the meter would no more know which satellite it was pointing at than an amoeba would know the difference between a car and a lorry, just that both seem pretty big. More fiddling, and a slightly damper tea-towel and a second 'peak' was found. Another tune of the receiver and 'Allelujah!' channels that were being transmitted from 19.2 East were found. But only from one transponder...

dish alignment girlWhat could this mean? Was it that the dish was roughly aligned but that only the very strongest signal was being received? Was it that the LNB was faulty? Was there a fault in the cable from the dish to the receiver indoors? Any (or all) of these could be the problem and with nothing more to go on, it seemed that the only way to resolve the issue was to resort to carting the TV and receiver outdoors so that the screen could be seen from the location of the dish. Doing this would mean that the 'signal strength' and 'quality' bars on the receiver's on-screen menu display could be used to point the dish more accurately.

A new patch lead from the dish to the receiver was fitted with F-connectors (thereby ruling out any problem with the coax feeding indoors). Power up... And the receiver is showing 100% signal strength (very good!) but a signal quality of only 60% (OK but not brilliant). No amount of dish repositioning would yield any improvement and still just the one transponder was receiveable. Before giving up and ordering a new LNB, and with an increasing level of suspicion building up, the meter was taken out of line so that the dish was connected directly to the receiver without the meter in circuit.

Hey presto...! Now the receiver was showing 100% signal and 80% quality and, wait for it, all of the transponders on the satellite could be received. A final fine-tune of the dish position and the quality of reception was increased to 90% - not a bad result at all. Moving the TV and receiver back indoors to the other end of the original run of coax and this excellent result was maintained. It seems that the meter may have been overloaded by the signal from the satellite and was somehow distorting the signal (possibly it was generating harmonics or intermodulation products).

So the lessons from this cautionary tale are:
  • Don't use cheap 'satellite finder' meters to help align dishes, they cause more problems than they solve.
  • Stick to the tried and tested methods and just move a TV and receiver to a place where they can be seen from the dish and use the receiver's signal meter for alignment.
  • Damp tea-towels should be used for wiping down surfaces in kitchens and not for the setting-up of sensitive electronic equipment.

At this point you're probably thinking that this is the end of this cautionary tale, but you'd be wrong... there's more to come! Stay tuned to Wireless Waffle for our next extremely uninspiring episode of: HOW NOT TO INSTALL A DISH.
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Nuff sed...?signal strength
Friday 27 February, 2015, 15:09 - Spectrum Management, Much Ado About Nothing
Posted by Administrator
Experts at the University of Surrey have allegedly achieved wireless data transfer speeds of 1Tbps (Terabits per second), albeit in laboratory conditions and over a distance of just 100 metres. Sizzle! Then again, just imagine the cost of rolling out the 10 million or so cell sites that would be needed to cover the UK. Ow! Nonetheless this is a significant achievement. Yay!

1tbps zoom zoom

Mobile data connections working this fast would be able to transfer the contents of a blu-ray disk (typically 50 GigaBytes) in just under half a second. Wow! At typical current average mobile internet tariffs, the cost of transferring the data for the blu-ray would be around GBP200. Wowzer! Assuming you wanted to do this every day, the monthly cost of your mobile contract would be around GBP6000. Zowee!

Do we really need to say any more?
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DAB Dead Line?signal strength
Friday 30 January, 2015, 14:48 - Broadcasting, Licensed
Posted by Administrator
ofcom logo 1Yesterday was the final day for applications to Ofcom for a new national digital radio (DAB) multiplex licence. The licence was first advertised on 1 July 2014 with a deadline for submissions of 31 October. The deadline was then extended to 29 January to, according to a516digital, "allow a prospective licence applicant sufficient time to obtain information from Arqiva, which owns many DAB transmitter sites."

Two companies have applied for the licence:
  • Listen2Digital: A joint application from Babcock Media Services and Orion Media, a commercial radio group. Babcock Media run the transmitter network for BBC World Service.
  • Sound Digital: A consortium of Arqiva, a transmission company, and commercial radio broadcasters Bauer and UTV Media GB. Arqiva is the monopoly who run the existing UK digital TV, DAB and the majority of FM transmitters.

This year will mark the 20th birthday of DAB radio. According to Ofcom's latest digital radio market report:
...over the full 12 months to June 2014, digital listening (including DAB, DTV and online) accounted for a 36.3% share of all radio listening hours.

Note that this includes listening on digital television (DTV) and online via the web. The same report also states that:
Two-thirds of digital radio listening is through a DAB set.

Taking both of these into account, the report shows that DAB accounts for just under 24% of all radio listening hours. Of the digital-only stations, only 5 have audiences of over 1 million listeners.

Station Audience Audio Quality
BBC 6 Music 1,855,000 128 kbps, stereo
BBC Radio 4 Extra 1,654,000 80 kbps, mono
Absolute 80s 1,168,000 64 kbps, mono
1Xtra from the BBC 1,099,000 128 kbps, stereo
Radio 5 live sports extra 1,039,000 64 kbps, mono

For comparison Absolute Radio reach 1 million listeners in London alone, using one FM station and not a network of dozens of national (and expensive) digital transmitters. Capital Radio, BBC Radio 2 and BBC Radio 4 all have over 2 million listeners in London. The cost per listnener, therefore, for digital services is far, far higher than for older technologies which is in part, forcing the quality of the services down (and into mono). That being said, these digital-only stations have larger audiences than any station outside London (Free Radio in Birmingham, arguably the largest station outside London, reaches around 380,000 listeners).

As is clear from the table above, many services, even the popular ones, are in mono on DAB (though in stereo on-line and on DTV) and use very low bit-rates (remember that these are encoded in mp2 not the more common and higher quality mp3). The low bit-rates and mono signals mean that many of the services sound dull and lifeless compared to their analogue, FM, competitors.

Though Ofcom paint an upbeat picture, in particular citing that digital radio listening has increased by 2.4% over a 12 month period, this hides the fact that digital's share of listening has stagnated over the past year (it was 36.8% in the second quarter of 2013 and exactly the same in the second quarter of 2014).

dab technologyThe new national digital radio licensee, once on-air, will be able to run DAB+ on their multiplex which will at least offer the use of mp4 audio encoding and hopefully, therefore, better quality audio (though it does not stop them using even lower bit-rate mono). The bigger question has to be whether there is really a business case for digital services. The cost of transmission is high, listenership is low (and not growing significantly) and the quality is poor. Which is exactly why medium-wave broadcasting is dying a death.

Ofcom has set criteria that will determine when the time is right to switch-off analogue transmitters and go fully digital. It requires that 90% of the UK has a digital signal and that 50% of listening is on digital radio. With digital radio listening stuck below 40% and no real signs of growth, it looks as if these criteria will never be met. Of course if you applied the same criteria to FM broadcasting, we would be switching off digital radio today.

dabradioUnless something fundamental changes, it's difficult to see how DAB is going to suddenly become the default method of listening to radio. Even listening via the Internet (using apps such as TuneIn) will be unlikely to become the default method of listening to radio given the simplicity and low price of FM radios (and the fact that listening on FM does not use any of your monthly mobile data allowance). The only way this could happen is if there is a ban on the sale of FM radios. It would, however, be political suicide for any regulator to enforce such a ban as both broadcasters and listeners would no doubt complain very vociferously.

So what is the future of DAB? Does it have one at all? Or is it time to set a DAB 'dead-line' and turn it off? Your views and thoughts very welcome!
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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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