Wireless Waffle - A whole spectrum of radio related rubbish
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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Spray-On Antennasignal strength
Monday 27 February, 2012, 14:13 - Radio Randomness
Posted by Administrator
Regular readers of Wireless Waffle will be familiar with our relentless drive to improve both the availability, performance and aesthetics of antennas that can be used to listen to radio signals in situations where normal aerials are not feasible.

The Wireless Waffle Super Signal Holiday HF Antenna Apparel (WWSSHHFAA), a cunning aerial designed to go almost unnoticed on the wearer (though anecdotal evidence suggests that it does cause the wearer to become highly noticeable) which we updated in 2010, is one such solution. Whilst there are many examples of the WWSSHHFAA on beaches across the beaches of the Mediterranean, we have yet to receive an offer from anyone wishing to put it into full commercial production.

spray on antenna kitWe were surprised, therefore, to recieve a tip-off about an antenna that, in principle, can surpass the performance of even the WWSSHHFAA in quality of reception, in its ease of application, and its resulting aesthetic manifestation... Go and take a look at the Spray-On Antenna!

The Spray-On Antenna is, in essence, a metallised spray which coats whatever it is sprayed on with... metal. As metal conducts electricity, it can, of course act as an antenna. Thus by spraying any everyday thing with metal paint it will become an antenna. If the resulting metallised object is connected directly to the transmitter (the tools for which appear to be provided with the spray-on antenna kit) it can be used as an antenna. If it isn't it can still be useful as a reflector. A reflector on an antenna is just like a reflector on a flashlight or car headlight, it refocuses emissions that would otherwise have been heading out in the wrong direction and points them in the right direction. Putting a reflector behind a transmitting antenna therefore focuses power in the opposite direction. How effective it is depends on a number of important factors such as:biquad antenna
  • The relationship between the size of the object that has been sprayed and the wavelength of the frequency being used - ideally the two would be harmonically related, or at least the antenna/reflector would be larger in wavelength than the frequency being used.
  • The distance between the reflector and the transmitting antenna (if used as a reflector instead of an antenna).
  • The specific shape of the antenna or reflector. For antennas, a line (like a wire) is good. For a reflector, parabols are good (as with satellite dishes), flat panels can work (see picture), otherwise a thin line will work as long as it is the same polarisation as the transmitting aerial.
pretzel antennaSo just about any object could be used to enhance reception. On the left here is a 'pretzeltennna'. The pretzeltenna, if placed at exactly the right distance behind, for example, a cell-phone could act as a reflector and boost signals in one direction. Alternatively two pretzeltennas could be used to form a 'dipretzel', centre-fed with coax cable. The advantage of a dipretzel is that, if you get hungty, you can feed yourself with it too (though the metal spray might poison you).

For those on holiday with no way of stringing up antennas (the problem that the original WWSSHHFAA was designed to overcome), the concept of using a spray-on antenna provides a new and interesting way ahead. A comparison of the two solutions is shown below. On the left, the original WWSSHHFAA, with hidden wires acting as an antenna stretched across the supporting structure. On the right, a spray-on antenna on a similar supporting structure. We have been unable to test the spray-on antenna in this configuration, though we would expect that it would significantly enhance reception given its larger conductive surface area.
wireless waffle holiday hf antenna apparel spray on antenna
Original Wireless Waffle Holiday HF Antenna Apparel Similar supporting structure with Spray-On Antenna

Post Script: We have received a message from Timothy Matthews from Polzeath, Cornwall. Timothy writes,
"I got, like, a can of spray-on antenna from, like, a local 'craft' shop and zizzed it on a few 's'pportin' structures'. I tried, like, tappin' in to the structures to extend my 'antenna' but all I 'received' was an extension to my overdraft, large, innit."

Well, Timothy, any kind of antenna of this type requires very delicate adjustment and we recommend that in the future, you 'leperately twelt them over the hish with a squench' as admirably described on the ropium web-site which is full of useless tips which make about as much sense as your e-mail.
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Make your ADSL connection more reliable!signal strength
Saturday 11 February, 2012, 12:52 - Amateur Radio, Radio Randomness
Posted by Administrator
A while ago on Wireless Waffle, I commented on the daily loss of service that was occuring on my home broadband (ADSL) connection. It seems that this struck a chord with a number of people and remains one of the most commented-on articles on the site.

The question is, 'can anything be done to fix this problem'? The answer seems to be, that for a few pounds (a few and a bit Euros, or a few and a half Dollars) you can easily make a device which will provide additional filtering on your ADSL line and help with the problem of interference on the line. This solution is not a 100% guarantee of an improvement but does help and has resulted in an enormous (almost complete) reduction in drop-outs and, to boot, an increase in connection speed on the Wireless Waffle line!

The increase in broadband connection speed is perhaps an odd outcome but this is a result of a more stable connection on the line. This is why... The equipment at the exchange sets a target 'signal to noise (s/n) threshold' for each line depending on how reliable the line is. If the line continually drops out, the target s/n is increased to provide an additional 'safety margin' to try and stop future drop outs. If the line remains stable for a while (typically a couple of weeks), the exchange notices the difference and will lower the target s/n threshold. Each change in threshold is typically 3dB (a doubling or halving of power) and results in an approximately 500 kBps change in line speed. The Wireless Waffle line was originally synchronised with an s/n threshold of 12dB and a speed of just over 2 Mbps. As a result of applying the solution about to be described below, over a month or so, the target s/n was reduced (by the exchange) to just 6dB and the connection speed is just over 3.5 Mbps! Even with only 6dB s/n the line has remained completely stable for over two months and has not dropped out again once.

So how does this miracle solution work. Well, the first step is to gather the teeth of some bats at full moon when wolves are howling. Add to this, three drops of lizard spittle and some onyx droppings. Only kidding! It's not magic it's just simple electronics!

The solution comprises two simple pieces:
  • A common mode choke which serves to remove any non-common mode signals from the line
  • A low pass filter to get rid of any noise on the line which is outside the range of the ADSL signals
Signals on an ADSL line should, in theory, be balanced, meaning that of the two wires used for the connection, the signal on one wire should be the direct opposite of the signal on the other. But there are a number of wiring and other issues which can lead to this not being the case, and in particular can lead to interference becoming present on both wires, but in an unbalanced way, or even just on one wire. Any unbalanced signal which is on both wires [u]should[/u] be filtered out by your ADSL modem but it seems that giving this an additional bit of assistance with an external 'common mode' choke can make a helpful difference.

The low pass filter just stops any signals arriving on the line which are not needed for ADSL from getting into your modem and causing havoc. This could be strong short or medium wave broadcast signals which appear after dark, or could be strong local transmissions from a nearby radio amateur. Three different filter designs are presented which have differing degrees of effectiveness and you can choose which is the best for your situation.

To make the Wireless Waffle Anti-Daily Service Loss (or WWADSL) device, you will need:

1. Two pieces of (single core) wire, around 30 cm long
2. A ferrite toroid (eg FT50-43)
3. Two capacitors (either 1nF or 470pF - see below)
4. Two inductors (either 3.3uH, 4.7uH or 6.8uH - see below)
5. Six pieces (three pairs) of 'chock block'
6. An old phone socket to ADSL modem lead

No soldering is required and all the parts are reasonably readily available.

wire twistedLet's start with the choke. This simply consists of two pieces of (single core) wire, twisted together and then threaded through a small ferrite toroid. The exact number of turns is not critical, but the type of toroid is important. You need a ferrite toroid which are usually black in colour, rather than any other sort which are distinguishable by the fact that they are generally painted a different colour (eg red or yellow). Ferrite toroids usually have names beginning 'FT', such as FT37-43 or FT50-43. The last number (eg 43) is the type of material which is the important bit. The first number is the diameter of the toroid in hundredths of an inch. The one used here is an FT50-43 which is about the right size. An FT37-43 is a bit small. Ferrite cores ending 43, 72 or 77 are ideal for this project.

Take the two pieces of wire and twist them together, all the way along their length. Wind these around the toroid to leave yourself with about 2 inches of wire (5 cm) free at each end. The result should look something like the pictures below.

bifilar toriod 1bifilar toriod 2bifilar toriod 3

toroid chock blockConnect one end of the wires into one side of a double piece of chock block, and the other into another.

Now you need to take a decision... If your line synchronises at over 4 Mbps, the chances are you might be using ADSL2+. ADSL2+ differs in that it uses frequencies on the telephone line up to 2.2 MHz, whereas ADSL and ADSL2 only use frequencies up to 1.1 MHz. There are three choices of filter:
  • The 'mild' filter will allow all possible ADSL signals through including ADSL2+ and is suitable for all lines.
  • The 'medium' filter will still allow ADSL2+ through but might cause some loss of connection speed (at the expense of greater reliability of course).
  • The 'strong' filter will not allow ADSL2+ fully through as its frequency response begins to roll-off below 2 MHz and is therefore only suited if your line is running at speeds below 4 Mbps to start with.
None of these filters will affect ADSL or ADSL2 connections. You can see the frequency response of these filters in the diagram below: mild is the green curve, medium is blue and the pink curve is the response of the strong filter.

low pass filters

capacitors and inductorsEach filter is made of two capacitors and two inductors. The table below shows which values you require, depending on your choice of filter.

FilterCapacitorInductor
mild470pF3.3uH
medium1nF4.7uH
strong1nF6.8uH

Next take two of the inductors and a capacitor. On the opposite side of one of the chock blocks that has your choke connected, insert each of the inductors into one of the remaining holes and put the capacitor between the two holes. The other ends of the two inductors should now go into the final piece of chock block, and the remaining capacitor across the same chock block.

completed filterThe results should look something like the picture on the right (if you haven't spotted it yet, you can click on the pictures to see a larger one).

Finally, take the 'phone socket to ADSL box lead' that you have and cut it about 30cm from the end which goes into the ADSL modem. Strip back the shielding on both pieces, which will reveal some wires. If you have two wires, no more action is taken. If you find you have four wires, identify which are the middle two and cut off the outer ones (these aren't used). In the wire shown below the red and green wires are the inner two and the black and yellow wires can be disguarded.

Take one piece of the cable and insert the two wires into one end of your chock block construction - it doesn't matter which end. Then do the same with the remaining piece of wire, at the other end of your construction.

adsl plugadsl cablecompleted adsl filter

Bingo! You've finished. At this point it might be worth checking that there are no short-circuits. If you have a volt meter with a setting to measure resitance, check that:
  • there is a connection between the two ends of the filter; and
  • there are no short circuits across the chock blocks.
Replace the cable connecting your ADSL modem to your phone line with the new one you just made and Bob's your uncle.

It's probably worth stating, just to be certain, that this is for ADSL connections (ie that which comes into your property on traditional copper telephone lines). It won't work with mobile broadband, cable broadband or satellite broadband!

Let us know how you get on and whether the WWADSL filter helps. Perhaps you might also like to share your construction experiences or tips with others too.
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Harmonics - Putting The Record Straightsignal strength
Monday 23 January, 2012, 04:09 - Spectrum Management
Posted by Administrator
Over the years, Wireless Waffle has tried to explain and demystify many of the more esoteric technical terms and concepts used in the wireless world such as OFDM, intermodulation and even interpreting ionograms. There is one very straightforward technical concept that is so often misused that it's time the record is set straight. That concept is harmonics.

Harmonics should be the easiest concept to understand. Passing any radio (or for that matter audio) signal through anything that is not perfectly linear (and the only things that are perfectly linear are pieces of wire) will produce differing degrees of harmonics. The non-linear device will produce other things as well (such as the aforementioned intermodulation) but harmonics are probably the number one resultant.

A harmonic is simply a copy of the original signal but with it's frequency multiplied by an integer. The second harmonic is therefore the original signal but with all it's frequencies doubled.
  • The second harmonic of 1 MHz is at 2 MHz;
  • the second harmonic of 10 MHz is at 20 MHz;
  • the second harmonic of 150 MHz is 300 MHz;
you can clearly see the pattern emerging. harmonics of deep purpleMusicians will recognise the second harmonic as being an octive. The third harmonic is simliary the original frequency, but tripled. The third harmonic of 1 MHz is 3 MHz, and so forth. The n-th harmonic is the original frequency multiplied by 'n' so the 273rd harmonic of 2 MHz is... 546 MHz. You can even play the game with light (just about) as the second harmonic of deep red (almost infra-red) is deep purple (ultra-violet) which probably explains why so many wannabe rock groups use devices such as 'harmonisers' and 'harmonic sweetners'. The only rule is that 'n' has to be an integer. There is no such thing as the 'second and a halfth' harmonic, and this seems to be where the confusion arises.

As harmonics are so common, much effort is made to ensure that transmitters are filtered to remove them. A low pass filter is one which allows lower frequencies through but attenuates higher ones and is almost universally tacked onto the output of any transmitter. You would not want a high power TV transmitter on 534 MHz (UHF channel 29 in Europe) radiating strong signals at its second harmonic frequency of 1068 MHz, in the middle of the aeronautical safety band, any more than you would want an aeronautical system at 1068 MHz radiating at 2136 MHz and causing interference to 3G base stations!

mistress harmonicSo often, you will see spurious emissions from a transmitter being called 'harmonics'. Unless those emissions are on direct multiples of the main transmitter frequency they are not harmonics, but will either be intermodulation or could be caused by the transmitter squegging. Either way, the term harmonics seems to have been awarded a new meaning to encompass all spurious emissions from a transmitter. As a Wireless Waffle reader, now that you know different, any violations of use will be punished strictly and severely.

For completeness, it is worth pointing out that there are (very rarely) such things as sub-harmonics. These occur on frequencies that are integer multiples of integer fractions of the original frequency. As an example, a problem was reported by the operator of a private mobile radio system on 72.45 MHz of breakthrough from a co-sited FM broadcast station on 96.6 MHz. 72.45 is precisely three-quarters of 96.6. This rare problem was caused by the synthesiser in the transmitter which had an oscillator on 96.6 MHz which was fed into a pre-scalar that divided the signal by 4, producing an output at 24.15 MHz. This signal was rich in harmonics and due to the shoddy design of the transmitter, the third harmonic of this signal was being fed into the transmit amplifiers and appearing at the antenna output - nasty! An additional filter on the output of the FM transmitter cured the problem. It's perhaps no surprise that the company that made the transmitter in question (who won't be identified) is no-longer manufacturing them!
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