Wireless Waffle - A whole spectrum of radio related rubbish
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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Russia is the Tsar of Piratessignal strength
Thursday 19 January, 2012, 14:30 - Amateur Radio, Pirate/Clandestine
Posted by Administrator
Wireless Waffle has talked extensively about pirate radio in the past, from short-wave music stations, to Brazilian sat-jackers. But it seems that, of all the nations on the planet, the Russians hold the baton for being the biggest pirates of them all.

This story begins when reading the latest intruder report from the IARU Region 1 Monitoring System. The report indicated that there had been an intrusion into the 80 metre amateur band between 3.5 and 3.6 MHz by Russian pirate stations running AM. Now historically the Voice of Korea (the North Korean broadcaster) has been transmitting in the 80 metre band (or the 75 metre band as it's called in in North America) on 3560 kHz in AM and the immediate assumption was that these new signals couldn't possibly be Russian pirates, but must be the Voice of Korea and perhaps a few other stations trying to jam it. The IARU report, however, says that the carriers are very unstable and that the modulation is voices in Russian.

blue soldier red squareSo the only thing to do to verify this story is to turn on a receiver and have a listen. Having done this, there were no obvious signals in the 80 metre amateur band. Having previous heard pirates just below the band at around 3450 kHz, the tuning dial was slowly rotated to ever lower frequencies. Nothing. And then, at 3175 kHz, something. A weak carrier... no, two carriers alternating... both rather unstable in frequency. Switching the receiver to AM yielded weak modulation. A bit more tuning, to 3125 kHz and a much stronger AM signal with a Russian voice and a wobbly carrier. Hey presto!

But what are these odd signals? Are they military operators in a private net (if so, why AM and why unencrypted)? Are they some kind of harmonics or intermodulation? Googling didn't bring much until a page on Sparky's Web Blog was found. It seems that these are effectively the equivalent of Russian CBers but presumably using much lower frequencies given the large distances between Russian cities. The band is known as the тройка band ('troika' in English which has several meanings from 'three of a kind' to a sledge or fairground ride). The band runs from approximately 2900 to 3200 kHz which are internationally allocated to the Aeronautical Mobile and Mobile services.

red square blue squareThere are aeronautical frequency assignments in the band (2872, 2899, 2921, 2962 and 3016 are frequencies assigned to North Atlantic traffic for example), but these lower frequencies are less often used unless propagation makes it totally necessary. Oddly, the various frequency lists for the band show very little aeronautical use in Russia (other than Irkutsk on 3016 kHz) - a coincidence? Probably the pirates know this and therefore feel free to mess about in the aviation bands, knowing that the Russian authorities are likely to be little interested in their activities.

If you're in Europe, when it gets dark (and lower frequency propagation opens up over the continent), why not give them a listen. It's fun to chase the carriers up and down in frequency. If you speak Russian, perhaps you could provide some translation as to what on earth they are talking about!

P.S. You might also want to take a listen to 2920 kHz USB as this seems to be a common calling channel for the more technically adept Russian pirates.
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Let's sheikh on it!signal strength
Thursday 14 July, 2011, 10:39 - Amateur Radio, Pirate/Clandestine
Posted by Administrator
Around the short-wave world, mention of 'PsyOps' has recently had reason to reappear. It refers to psychological warfare being conducted by NATO forces to 'scare' Colonel Gadaffi's forces into remission through a variety of activities. One of these activities is the broadcast of semi-threatening, warning messages to troops loyal to Libya's erstwhile leader.

commander soloThese messages have apparently been broadcast from a Lockheed Martin EC-130 aircraft known as Commander Solo overflying the region and are using the frequencies which belong to the 'Great Man Made River Authority' (GMMRA) which is Libya's authority responsible for artificially transporting water from wells in the Sahara desert via a big pipe to population centres in the North. Why NATO would have chosen these frequencies is not known, however there is (or was) apparently an ALE network on these channels that was presumably in regular use and hence there would be several receivers across the country in 'important offices' which would hear the PsyOps transmissions.

Frequencies reported in use by the GMMRA in recent times include 4200, 5037, 5047, 5300, 5368, 5768, 6884, 7000, 8161, 8200, 8800, 9218, 9250, 9375, 10125, 10375, 10404 and 11100 kHz. Previous reported frequencies also include 3000, 3900, 4050, 6800, 7805, 7900, 10215 and 10250 kHz (thanks to Btown Monitoring Post).

Of the above, NATO PsyOps transmissions have so far been heard on: 6877, 9376, 10125, 10404 kHz. Note that the 10125 kHz frequency is slap bang in the middle of the 30 metre amateur band but as this is a shared frequency with other services the transmission by the military does not contravene the ITU frequency allocation tables and is therefore, effectively legal. The use of 7000 kHz by the GMMRA is not, however, legal as this is an exclusive amateur allocation. Initially, many of the PsyOps transmissions were jammed (presumably by the Gadaffi regime) however they no longer appear to be so.

Here's the Wireless Waffle recording of Commander Solo on 10404 kHz made at 14:00 GMT on 12 July 2011. The transmission ceased at 14:20 GMT. The noise underneath the transmission also ceased around the same time, however whether the two are connected (ie the noise is an attempt at jamming) can not be confirmed. Given that this recording was made in the UK, it is clear that the power of the transmitter used by Commander Solo and his ilk must be reasonbly high. Judging by the signal strength and general propagation conditions at the time of the recording, a radiated power of at least 1 kiloWatt would seem about right. As normal HF aircraft radios have powers of at least 200 Watts, this seems quite feasible.

uk libya tradeOf course, all that the Colonel has to do to stop the NATO transmissions becoming a nuisance, is hand out free power line adaptors to at least one house on every street and all short-wave frequencies would be instantly jammed. Perhaps Colonel Gadaffi is an investor the Comtrend PLT devices that do all the damage and the reluctance of Ofcom to do anything about them is part of some previous UK-Libya trade agreement on arms sales. Surely now that the UK is part of a force against Gadaffi, Ofcom can now breach the terms of this agreement with the Libyan government to pollute short-wave and finally get rid of the menace of PLT?
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Bye bye 70cm, hello happiness?signal strength
Saturday 26 February, 2011, 02:18 - Amateur Radio
Posted by Administrator
On a number of previous occasions, Wireless Waffle has commented on actions being taken by various regulatory authorities which seem to be attacking the use of the 70 centimetre band by radio amateurs. But in the USA, things have just gotten a whole lot worse, with the tabling of a bill which suggests that two thirds of the (admittedly large) US 70cm allocation be given over to broadband services for first responders (or the emergency or blue light services as we call them over here).

six million dollar billThe bill, snappily entitled 'A bill to enhance public safety by making more spectrum available to public safety agencies, to facilitate the development of a wireless public safety broadband network, to provide standards for the spectrum needs of public safety agencies, and for other purposes.' or 'Broadband for First Responders Act of 2011' for short (herinafter referred to as 'the six million dollar bill') states, in section 207, subsection (d):
Not later than 10 years after the date of enactment of this Act, the paired electromagnetic spectrum bands of 420440 megahertz and 450470 megahertz recovered as a result of the report and order required under subsection (c) shall be auctioned off by the Federal Communications Commission through a system of competitive bidding meeting the requirements of section 309 of the Communications Act of 1934.

The spectrum referred to in the aforementioned subsection (c) and in section 207, subsection (a) appears to refer to that which is freed by the cessation of use by public sector users who should migrate to the 700 and 800 MHz bands in the interim. However, there is little, if any, use of the frequency range 420 to 440 MHz by these users in the first place, as it is part of the amateur band. Indeed, according to the United Stated Frequency Allocations the band is only to be used by either radio amateurs (on a secondary basis), or by Government radiolocation services (eg the PAVE PAWS radar installations at the Clear, Beale and Cape Cod air-force bases). So, if taken literally, the frequencies in the range 420 to 440 MHz which would become available are - none, because none of them are used and thus none have been cleared! However, things are never that straightforward and it could be argued conversely that the fact that the first responders are not using that range of frequencies is a clear indication that they have cleared out of the band!

Either way, this assault on the 70cms band might be time for US amateurs to think carefully and propose something in their mutual interest. North of the border in Canada, the 70cm band stretches only from 430 to 450 MHz and in most of the rest of the world it is only 430 to 440 MHz (and as indicated before, there were moves afoot in Europe to further constrict this to 432 to 438 MHz). It may be, therefore, that agreeing a reduction in the US 70cm band to be in line with Canada at 430 to 450 MHz whilst in return guaranteeing some certainty of tenure would be a good way ahead. In Europe, for example, a reduction to 432 to 438 MHz in return for clearing out all those annoying low power devices around 433 and 434 MHz and also guaranteeing primary status for amateurs in the band would be a fair compromise. Or what about making the 70cm band 430-433 and 435-440 MHz, thereby leaving the low power devices to wallow in their own crapulence, sure this would require the re-tuning of many repeaters in the UK and elsewhere, but this is already having to be done in many cases due to the incoming and outgoing interference problems caused by the self-same low power devices.

amateur harmonisationIn many countries around the world, the frequency range 410 to 430 MHz is used for digital mobile radio systems which support blue-light activities. In the UK some spectrum in this range is available for use by the Ambulance service, for example. This means there is equipment available. Equally the band 450 to 470 MHz is similarly used. Therefore, giving US first responders the ranges 410 to 430 and 450 to 470 MHz makes a lot of sense and for once, means that the US frequency usage would be in harmony with that of most of the rest of the world and harmonisation leads to economies of scale and cost reductions and so forth, as its protagonisist are always keen to argue.

Of course, any change in usage or allocation in a band leads to the need to re-plan, re-tune and re-think, but if the rest of the world's radio amateurs can cope with just 10 MHz of 70cm spectrum, and Canada can cope with 20 MHz, perhaps it is time for American amateurs to relinquish part of the band in the common good and figure out what they would like in return?
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