Wireless Waffle - A whole spectrum of radio related rubbish

Hop to it!signal strength
Friday 25 January, 2013, 13:45 - Radio Randomness, Spectrum Management
Posted by Administrator
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.

hf frequency hopper

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.

hop to itThere'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!
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Soldery Songsignal strength
Sunday 23 December, 2012, 23:02 - Radio Randomness, Satellites, Much Ado About Nothing
Posted by Administrator
It seems there are very few songs which touch on the topic of satellite communications unless you count:
  • Sleeping Satellite by Tasmin Archer;
  • Satellite by Lena (Germany's Eurovision winner in 2010); and
  • Satellite by Oceanlab.
But none of those songs are really about satellite technology as such, they just happen to have ‘satellite’ in their title. There are, however, some songs which have lyrics that are actually about satellites. For example:
I'm just talking to a satellite,
Twenty thousand miles up in the sky each night

Taken from Electric Light Orchestra's Calling America.

There’s also:
I saw two shooting stars last night,
I wished on them but they were only satellites,
It's wrong to wish on space hardware.
I wish, I wish, I wish you'd care.

Taken from Kirsty Macoll's New England.

So it was nice to be alerted to a piece of work which is not only about satellites, but is very specifically endorsing the use of C-Band satellite services (3400 – 4200 MHz) over and above the use of Ku-Band (10700 – 12500 MHz) in sub-Saharan Africa where C-Band reception is more reliable than Ku-Band due to the fact that it deals with rain fading much better than Ku-Band does.

The song is by Cameroonian artist Wes. In it, he laments the loss of his Ku-band equipment, and the main thrust of the song is that he is short of some solder with which to complete the installation of his new C-Band parts. The video has him stood in front of his non-functional C-Band dish whilst his team try to dance their way into fixing the problem. Eventually they set off on a trek to try and get him some solder as the dancing, no matter how energetic, is clearly not working.

The only odd thing is that there is an Asian lady who, all the way through the song, keeps going on about her blasted spade. Still, it all adds to the ambiance.

The song is called ‘Soldery Song’, and you will need to watch the video whilst at the same time reading the lyrics below as it is quite hard to follow what he is saying due to his strong African English accent (the spade lady's incessant moaning about her spade is shown in brackets)...

SOLDERY SONG – WES


Soldery Song – Wes by jibou

(My Spade, where’s my spade?)

Soldery song: me need a solder
Me got me some parts, now it's me too,
Old part me chuck, and new me part, yeh?

Soldery song: me need me a soldery solder
Me got me some parts, now it's me too,
Old part me chuck, and me new part, yeh?

I throw a my Ku away, melt some solder, done my way
I throw a my Ku away, melt some solder, done my way

Bring us C-band way (with a spade?)
One-a-where they can go?
Hey, I meant to check.
(Spade, yeh, yeh, yeh, yeh!) x 2

Soldery song: hoo hoo hoo hoo hoo, me need a solder
Me got me some parts, now it's me too,
Old part me chuck and new me part, yeh?

I throw a my Ku away, melt some solder, done my way
I throw a my Ku away, melt some solder, done my way

Bring us C-band way (with a spade?)
One-a-where they can go?
Hey, I meant to check.
(Spade, yeh, yeh, yeh, yeh!) x 2

No more can I Ku, new me parts C-band
No more can I Ku, new me parts knackered!
No more can I Ku, new me parts C-band
No more can I Ku, new me parts knackered!
No more can I Ku, new me parts C-band
No more can I Ku, new me parts knackered!

I throw a my Ku away, melt some solder, done my way x 4

Bring us C-band way (with a spade?)
One-a-where they can go?
(Spade, yeh, yeh, yeh, yeh!)
Bring us C-band way (with a spade?)
One-a-where they can go?
Hey, I meant to check.

No more can I Ku, new me parts C-band
No more can I Ku, new me parts knackered!
No more can I Ku, new me parts C-band
No more can I Ku...
(Spade, yeh, yeh, yeh, yeh!)

Perhaps some kind Wireless Waffle reader could purchase some solder and send it to Wes to get his C-band equipment up and working. Oh, and whilst you’re at it, give the poor lady a spade too.
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Is 5 better than 2.4 (GHz)?signal strength
Thursday 9 August, 2012, 15:13 - Radio Randomness, Spectrum Management
Posted by Administrator
wi five logoAlthough the standard for WiFi at 5 GHz has been around for a long time, most manufacturers have focused upon producing equipment for the 2.4 GHz band. The reason for this is a simple one - it's cheaper! The higher you go in frequency, the more difficult, and therefore expensive, it becomes to transmit and receive radio signals. As a result, home routers, laptops, smart phones and other devices have almost exclusively been equipped to use the 2.4 GHz band for their WiFi connection.

Previous Wireless Waffle articles have discussed how to select the best WiFi channels in the 2.4 GHz band, and other techniques, to maximise coverage and signal quality, however we have not looked at the 5 GHz band. Recently, there seem to be a slew of articles which are claiming that using 5 GHz will produce better range and more reliable connections compared to 2.4 GHz. The logic of these articles seems to go '5 is a bigger number than 2.4 - in fact it is more than double - so it must be at least twice as good'. This, sad to say, is not the case. Here are the real facts:
  • Signals at 5 GHz only travel HALF as far as those on 2.4 GHz as higher frequencies have poorer coverage than lower ones.
  • Signals at 5 GHz will struggle almost TWICE AS HARD to get through walls than signals at 2.4 GHz due to their poorer propagation characteristics.
  • 5 GHz WiFi equipment is subject to exactly the same POWER RESTRICTIONS as that for 2.4 GHz, so there is no inherent advantage in terms of the technology itself.
  • The use of some of the 5 GHz channels is subject to the requirement to STOP TRANSMITTING if a nearby radar is detected. No such restriction applies at 2.4 GHz.
  • 5 GHz equipment will be (slightly) more POWER HUNGRY than its 2.4 GHz counterparts, increasing battery drain especially in mobile devices.
  • 5 GHz receivers are likely to be LESS SENSITIVE than 2.4 GHz receivers because of the increased difficulty of making low noise devices at higher frequencies.
  • The 5 GHz band consists of up to 25 (territory dependent) independent channels which can be used without interfering with each other meaning there is much GREATER CAPACITY for more networks, whereas the 2.4 GHz band has 13 channels of which only 3 can be used independently.
  • The 2.4 GHz band is also used for Bluetooth, microwave ovens, wireless cameras and many other applications meaning it can be subject to a lot of background interference. The 5 GHz band is MUCH CLEANER, though the band is not exclusive to WiFi systems.
  • There are still fewer 5 GHz devices around than 2.4 GHz once and hence it is likely to be LESS SUSCEPTIBLE TO SNOOPING.
As coverage is determined both by signal strength and by the amount of interference, it is therefore possible that people in particularly densely populated areas where there are lots of 2.4 GHz users around might find that the 5 GHz band provides a more reliable connection and may even provide greater coverage. In most cases, however, the 2.4 GHz band has many advantages and the claims being made that 5 GHz is somehow 'twice as good' are just plain wrong.

For a home network, in a small house or apartment, using 5 GHz may offer some advantages given the lower interference it will suffer from other devices, but in large family homes a 5 GHz WiFi router is unlikely to be able to outperform the coverage and range that a 2.4 GHz router achieves.

five is betterWhere the 5 GHz band may come into its own is when the not-quite-yet-finalised IEEE 802.11ac standard is adopted. This works in the 5 GHz bands and uses the greater capacity of the band to deliver connection speeds of up to 1 Gbps. For streaming media around, this has clear advantages. As a wireless distribution for a home internet connection, however, there is unlikely to be any improvement noticeable using 802.11ac than with the existing 802.11n standard which can already offer connections of over 100 Mbps - much faster than most home internet connections!
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Super-Resonant Frequency Memocorderssignal strength
Sunday 1 April, 2012, 18:59 - Radio Randomness
Posted by Administrator
One major problem facing many authorities across the world, is the transient nature of radio transmissions. For example, tracking down a radio transmitter requires the transmitter to be active in order for its direction to be sensed. Equally, for those bodies (such as the security services) who wish to capture radio transmissions of various sorts, especially those thay may be of short duration, the only way is to place sophisticated and costly wide-bandwidth receivers in a particular location which record everything they receive onto a hard disk, the data from which has to be analysed at great expense.

How much simpler it would be, if there were a device or material of some kind which would 'capture' any radio transmission and then store it such that it could be collected at a later date. Such a device should ideally:
  • require no power source to operate;
  • be able to store transmissions for an indefinite period;
  • be deployable and collectable by untrained agents;
  • not look out of the ordinary such that it does not arouse suspicion;
  • capture even the shortest burst of transmissions.
After having spent much time thinking about these issues, Prof. A. Lilo at the University of Travnja in Croatia (home, incidentally, to radio industry legend Nikola Tesla) has developed a device called a 'super-resonant frequency memocorder'.

Professor Lilo and team of the University of Travnja in Croatia
Professor Lilo and his team
The concept is not difficult to grasp. Imagine, if you would, a set of tubular orchestral bells or chimes. When struck, each chime resonates at a frequency which depends upon it's length (and on other factors such as the material it is made of). The chime would go on resonating forever (and thus producing the same note) if it could be suspended in a way which incurred no friction between the chime and its mount, and was in a frictionless environment (such as a vacuum). The only reason the chimes stop ringing is because of the method and medium in which they are mounted.

It is also not necessary to actually strike the chime for it to begin resonating. If a tuning fork which produces the same tone as a chime is held next to it, the chime will 'super-resonate' with the tuning fork and begin to reproduce the tone. If a tuning fork were held next to a chime in a frictionless environment, the chime would continue to produce the tone indefinitely, long after the tuning fork were removed from the area.

Using this concept, Professor Lilo has developed the 'super-resonant frequency memocorder' (or Spereo Quemord for short). The concept is almost identical. A dipole antenna mounted in a frictionless radio environment, which is one in which no alternative electromagnetic fields can 'usurp' or 'slurp' the energy contained in the dipole (known as an 'anti-uslurp field' such as that found in certain Faraday cages) will continue to resonate and thus repeat and store any signals which excite it. The difficulty is coupling the dipole to the outside world whilst maintaining the anti-uslurp field and it is this element of the 'Spereo Quemord' which is still under wraps.

By using a number of Spereo Quemords of different but similar sizes, it is possible to store and record radio transmissions over a range of frequencies. Retrieving any signals stored is simply a case of removing the anti-uslurp field at which point the stored signals are re-radiated from the dipoles directly replicating the transmission which originally excited the Quemords.

spereo quemord prototypeThe first prototype of the device was built unobtrusively into a piece of chair-shaped lounge furniture and placed into the waiting room in the University's health centre. At the end of the day, the device was taken back to the laboratory where the elements of the device which generate the all-important anti-uslurp field were removed. The team at the University were able to recover some 2G and 3G mobile signals as well as several hours of WiFi, a number of short transmissions from a passing security van and even the lunchtime news on the local community television station, 'Travnja budale šala TV' (TBS).

spereo quemord 2Flushed with their success, Professor Lilo and his colleagues have gone on to build a piece of furniture made exclusively of Spereo Quemords which they have used to demonstrate its capabilities at various venues. Their greatest achievement to date was to record and reproduce very weak signals from GPS satellites causing all the GPS devices in the room to show their position as being that where the device was originally located (and where it recorded the signals) and not in the room in which it was being demonstrated!

The next stage is to attempt to reduce the size of the Quemords which Professor Lilo believes will be possible using room-temperature super-conductors which will allow the dipoles and the anti-uslurp field generators to be made almost infinitely small. They believe that it should be possible to develop a device which records and stores all transmissions on all frequencies in a unit no larger than a typical mobile phone, or small piece of fruit.

As always, Wireless Waffle likes to keep you up to date with the latest developments in radio technology. Rest assured that as soon as there is any further news on this exciting piece of radio technology, you will here about it here first.
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