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The working end of one of my experimental 2.2GHz
Yagi aerials made of 2mm brass rod, cable ties and glue!

NEW SECTION MAKE YOUR OWN "COAT HANGER" AERIAL NOW ON THIS PAGE

Home made 3G aerials

Connecting from a static location is rather different to using your dongle when out and about. When in a fixed position it is possible to use a directional Yagi type of antenna array - that's a small TV aerial to you and me. This design was invented by a Dr. Yagi in Tokyo in 1926 and now used on almost every rooftop in the world. The good thing is that 3G broadband uses much higher frequencies than TV so the aerial is correspondingly much smaller (frequency α wavelength), in fact a good one can be less than a foot long. You can see a couple of pictures of my prototypes on this page. To make one similar you need smaller parts than for a telly aerial and a model shop should have all the necessary metal (except the plug, which you can also make, see below) for under a tenner. Not bad when 3G Yagis are sold for up to £200 on some web sites! (The manufacturers sometimes hide them in a plastic pipe to make their device look more modern, but inside it's just bent metal!)

I have now made several Yagi style aerials for 3G using modelling brass strip and most work well, but to be honest none as well as I would hope, so it's still a work in progress. In theory a good Yagi tuned to the correct frequency could give a 15dB gain, mine give about 9dB, but that is still an increase of 10 times or going from one bar to 5 bars so still thoroughly worth doing! The lack of signal strength may be down to my building accuracy. The director strips need to be cut and placed to an accuracy of 1mm or less. Such tightness comes hard to a spectacle wearer, but I'm working on it and hope to improve signals a lot before publishing my design. However I have read reports that some of these expensive units sold on eBay don't work that well either. I have recently built a simple flexible whip (a bent cloths hanger) and this works surprisingly well, with the advantage that a whip aerial can be put on a rooftop easily and left outside when it rains.

Further down I will describe my simple Yagi aerial but must point out that the design may well be modified in the light of experience.  The "bent hanger" whip will be the next item on the page.

 

"Cheap 'n cheerful" CRC9 Huawei 3G dongle aerial plug

More drawings are in preparation - please look back in a week or two


A couple of my early prototype plugs without cable


An adapter to fit an Huawei dongle to a standard aerial

Before you start you need to be able to connect to your broadband dongle so first I will give you my simple cheap design for a plug to fit the aerial socket on Huawei 3G dongles. You can use these plugs to connect your experimental aerials. I haven't seen this size of plug - called CRC9 - for sale at less than £5. My design, which I have now repeated many times costs perhaps 20p in parts and works pretty perfectly. It may not be as beautiful to look at but who cares - it works, and if you drop it on the floor and lose it then just make another!

To make a plug the size of a CRC9 to fit the Huawei socket you will need, a small piece of thin brass from a model shop, a 2mm drill (used for size so can be blunt!), a piece of tube from a can of WD40 or similar - 2mm tube is often used for squirt aerosol products, then some Araldite - preferably rapid cure, soldering equipment, and a small piece of brass wire or failing that use some fuse type wire or perhaps even in an emergency a paper clip. Plans below.

Cut a piece of brass to 6 or 7mm x 10mm. Roll this round the blunt end of the 2mm drill as this will be slightly over size and you actually need 2.2mm internal diameter to fit the socket. When you make the cylinder it is helpful if there is a small gap left (in other words not quite a complete circle) as this will make it easier to "spring" and fit tightly.  If your drill is a bit small you could of course wrap a piece of paper round the drill former first to make its diameter slightly larger. To the end of your newly made brass cylinder tin a small part for easier soldering later without overheating and melting the plastic. Cut off two "ears" from the corners of the end of the brass away from the dongle to make a place where you can bend the centre wire over without shorting out. Look at the diagrams and photos, they are much clearer and to be honest you could do the job just by looking at them without bothering to read these words at all!

Next cut the tube about a couple of mm long, this is your insulator/spacer. Push a few mm of the wire through the spacer and bend over the end. Chose a size of wire that is a firm fit in your dongle socket, not too lose nor too fat. I used a piece of wire from a capacitor, you might use some old fuse wire or brass wire if you can find it. Fix this wire in place with a tiny blob of Araldite at the "top" end away from where it will go into your dongle as you naturally don't want to put Araldite in your dongle!  After this has dried push the spacer with its wire attached through to line up with the back end lining up the wire bend with the two "ears" to avoid a short circuit. Fix in place again with another small blob of Araldite. It's worth making up several of these plugs at one time as it is impossible to make a small enough blob of Araldite and anyway the parts will be to hand. You can always use the best ones and junk the rest.

After this solder on your co-ax connecting cable screen to the previously tinned brass strip, centre to centre, and then cover the end up with a blob of Araldite shaped when almost dry to make a handle to push and pull when inserting. Set this entire unit aside to dry properly, 24 hours minimum.

Here is a tip. You should really ensure that the wire is central while the Araldite dries - overnight is best - and it might fall to one side while drying. I usually risk it and leave the plug just slightly in the dongle socket while it dries. If you are going to make several of these plugs then you might prefer to make up a small fake socket or perhaps just use another piece of WD40 tube (unglued) to hold it all in alignment. A little grease will stop the tube sticking while the Araldite dries.

Finally cut the wire so that it protrudes about 4mm or so out of the end of the brass screen and there you are! A cheap 'n cheerful plug to attach your experimental aerials to your Huawei dongle!

 


The brass is cut to roughly this shape and then rolled into a cylinder.


My attempt at a diagram of the plug design.
The WD40 tube is just used as an insulator.

 

A homemade 2.1GHz Yagi antenna for 3G broadband

Now it's time to look at how you might make a Yagi aerial (antenna) to improve your 3G mobile broadband reception. The advantage of using a Yagi type of aerial is that first it is directional. By its very design it will reject signals coming from the side - in this design it will only accept signals coming at an acceptance angle of 35degrees. That means that signals from the side at 90 degrees, or to a lesser degree from the back at 180 degrees will be at a much lower level than those from the front.

This is a neat way to help with the problem described above when there is a source of interference at the side or back. So why try my "device" and why not use a Yagi for every purpose? The answer is the connecting lead. You see it attenuates or reduces the signals - a lot! If an aerial gives a gain of say 12dB (that's a lot in this design) then after going down a 10 metre lead of normal quality you will actually end up with less signal at the plug than using a small whip aerial with a one metre lead!

If this were a TV reception problem then we might consider a device called a pre-amp. This sits right on the back of the aerial and amplifies the signals before they go down the lead. That wouldn't work on 3G broadband as we need to send signals in both directions, both up and down. A suitable two-way device could be designed but it would be both difficult and expensive to build ourselves! Anyway, we will describe here the design of a Yagi and leave it to you to put it on the shortest low loss lead possible. I recommend that you use 2 metres of cable maximum if at all possible. Using really good quality cable you will lose about 1 bar per metre of cable. This means that if you put the dongle right on the back of the aerial and get 5 bars signal, 2 metres away you would only see 3 bars. So keep the aerial lead as short as possible and use an extension (possibly amplified) USB lead.

The quarter inch (6mm) square metal strips that we will use for the centre spine of our aerial are sold by model shops in 30cm lengths so we will design an aerial to fit on such a back bone after allowing an inch or two on the rear end for a mounting bracket. To build this antenna you will therefore need a single length of 6mm square box section brass and several lengths of 2mm solid brass rod, also some solder, plumbers solder is best, some flux for tinning and a hot soldering iron or a blowtorch. If you don't have a blowtorch available then you can stick most of it together with Araldite and leave the soldering just for the cable connection to the active element. Alternatively use your gas cooker when your wife is out! Total price for the metalwork is about £5 or £6. on top of this you will need some suitable co-ax lead (details of how to obtain this cheaply later on) and one of my famous home made Huaweii dongle plugs! Total cost for the whole thing, less than £10! This setup can increase your signal level from no bars to 5 bars. It really does work!

Again I will stress that you should connect this aerial to your dongle by the shortest lead made of the highest quality cable. Ideally less than 2 or 3 metres long, use anything over 8 or 10 metres and even with the best cable available you'll end up with less signal than you started with! So if you have plans to put this aerial on your chimney consider putting your dongle under the slates on a long amplified USB extension. In the past it wasn't possible to run USB devices more than a couple of metres from your computer. Now that amplified extensions are available this can be increased to 10 metres by putting two 5 metre leads in series. The manufactures of the extensions claim that you can daisy chain up to 5 leads together to get 25 metres away. In our experience no computer can supply sufficient current through its USB socket to run so many amplifiers plus a dongle. You could try a self powered USB hub but we still doubt that 5 leads in line would work.

If you absolutely have to get this far away from your computer then use a device called an Ethernet USB extension. This uses two special adapters at each end and a normal network lead in the middle - up to 30 metres does work, and up to 60 metres may work. The one drawback (apart from cost) is that with a high current device such as a 3G dongle you absolutely have to have mains power at the far end of the connection. Hardly convenient on your roof in a a rain storm!

Here are some sizes to get you working on your home built 3G aerial.

You will need something to act as the centre spar of the aerial. It is interesting that this plays no part in the actual workings of the aerial but I used 3/8" square brass section. You could use any metal, plastic or even wood. Obviously brass takes solder so if you use non solderable spar then you can glue the elements on, should make no difference to the final result. The elements (these are the bits of metal that go from side to side) can either go through the centre spar by drilling or can be mounted on the side of the spar. Again this makes no difference.

 (May 2012, still working on the site - more soon)

 

"Coat hanger" aerial made from the contents of your rubbish box

I have hesitated from publishing designs until I felt they were easy to make, were reproducible and above all that they worked! I have now built a half dozen "coat hanger" aerials that should give you a useful increase in signal strength if you are struggling to get a good mobile broadband signal. I am not saying that this design will make a huge difference but you should get a decent increase and if you make the design as described it should cost you less than £1 GBP in total, so hardly a huge outlay even if you throw it in the bin in the evening!

Parts list

A piece of thick wire (an old wire coat hanger thickness is ideal) This must be able to be soldered at one end so steel or copper wire is best.
A large heavy washer to act as the ground screen, the thicker and heavier the better!
A small piece of wood to act as a base. You could also use any other sort of non-conductive material but it needs to be fairly heavy to stop the whole thing falling over!
You will also need the real thing or one of my plugs shown elsewhere on this page.
Finally a metre or so of screened wire ideally a type suitable for 2GHz (TV aerial or satellite wire is a bit thick and inflexible but would do at a pinch). Do not use more than about 1 metre length or you may end up with less signal than you started with!

You will also need some simple tools, an accurate ruler, pliers, wire cutters etc., and a drill or piece of dowel to act as a former. If using a drill to wrap around it can be blunt. Glue of some sort is also needed, Araldite or hot melt glue would be ideal, the stuff from the 99p shop is fine.

I am going to give you the sizes for an aerial to help increase signals with a Three network dongle. As this uses its own specific frequency you won't get such good results if you use it on Orange, O2, or any other networks in the UK.

Method

Start by straightening the wire and then cut to a length that you can work with, about 50cm is a good place to start. I cannot be more specific as it all depends on the thickness of the wire that you are using. You have to make two coils in the wire, both of two and a half turns. So you will have to experiment a little to get it right, start at the bottom end bending and measuring as you go and then cut the final 10cm. The three lengths shown on the diagram are important, the wire thickness is far less so. You now need to start measuring and here accuracy is everything, so measure twice and bend/cut once!

To make it clear the 6cm, the 9cm and the 10cm are important, but you will need to work out how much wire is needed for the two two and a half turn coils. I have guessed that you will need a total of about 50 cm. With the coils having an internal diameter of 1cm using pi seems to equal 8cm for each coil. Is that clear? I hope so!

Right, you have cut your wire and now need to put in the first of the coils which starts 6cm from the bottom end but the wire may be a bit longer if you want to push some wire into the base. As long as the washer sits 6cm from the bottom of the bottom coil then the matching will be fine. As mentioned the coils have an inside diameter of 1cm so using an old 1cm drill as a former would seem the easiest. If desperate you could use an old wooden spoon handle as I did for one of my early efforts! The coils are 2 and a half turns, no more, no less or you will not get a good match. The photo should make it all clear.

Next attach the centre of your connecting wire to the 6cm point at the bottom end of the aerial wire. You really need to solder this to get a good connection, any thing else would be a bodge.

Pictures above of one of my experimental designs to give an idea of the manufacture of the coil. The centre picture also shows the gap between the two coils. I used some plastic covered garden wire for this aerial. The wire inside was a lovely rusty steel wire that after it was cleaned up took solder beautifully. This for a correspondent who asked for more info. Sorry, I have had health and technical issues lately and have lost the original message. The main point is that the coil should be central about the upright. If you off set the coil the sensitivity will not be unidirectional and you would have to twiddle the aerial round for best reception. By the way you can try putting your aerial at 45degrees rather than dead upright, this can increase signals by 1 bar.

The next step is to get a signal from your new aerial into the dongle. As I mentioned previously you really need to use a low loss flexible cable which is not so easy to get hold of so here are a couple of suggestions. I managed to get hold of a 9 metre Wi-Fi aerial extension lead complete with plugs for just £3 on eBay. Unlike an aerial which has to be made for a certain wavelength or frequency connecting wire designed for a slightly different frequency will work perfectly on 3G. Just cut to length (as short as possible remember - 9 metres is far, far too long), attach one of my simple plugs (or buy the right thing) and solder the other end to the aerial. If you don't want to go down the eBay route then believe it or not a simple screened lead that is used for audio will work after a fashion as long as you keep it as short as possible - not more than a foot or two will at least give you something to experiment with. I always keep an eye on the rejects box at my local supermarket and buy any unboxed incomplete audio or video leads and accessories there. I have picked up unwrapped switch boxes with useful switches and wires inside for £1 and incomplete audio or video lead sets for 50p!

I will look in the Maplin shop the next time that I am in the area (which is when I visit the hospital) to find a suitable lead part number that I can recommend and will report back a.s.a.p.

Now we move onto the base of the aerial which needs to be able to support the thing without falling over. This is made by drilling a small hole the same diameter as the wire. You stick the end of the wire into this hole to make the aerial stand up (doh!). Now the clever bit is that you then put the largest heaviest and largest steel or other heavy metal washer that you can get hold of to the top of the block of wood or plastic that you are using for the base. Look at the diagram (on the way) to see how this all works. The centre of your connecting wire is attached to the bottom end of your aerial wire and the screen of the connecting wire is attached to the washer. The washer MUST NOT make physical or electrical contact with the aerial. In this way the washer acts at the electronic base against which the signal "pushes" out. Solder the screen of your wire (that's the outside of the wire) to the washer and the centre of your wire to the bottom of the aerial itself. You can if you wish make the bottom part of the aerial (that's the 6cm part) a little longer and use the extra as the part that you push into the base. As long as you attach the connecting wire no more than 6cm from the bottom coil the aerial sees just this part and the matching is not affected. To make this clear the washer is placed 6cm from the bottom of the bottom coil and the circuit simply ignore the part that is stuck into the wood. Hope that's clear! Later on I will suggest ways to tune the aerial to the exact frequency. You do this by lifting the washer up and down nearer and further from the bottom coil. This is quite difficult (for example you have to move your hand completely away as you adjust so you can't just hold it and watch the signal level) but getting it right can make a real difference in gain so I will write a separate section to clearly explain how to do this. Using the above figures will give you good gain without any fine adjustment, so it's up to you.

How large should the washer be? The larger and heavier the better - it must be of conductive material, steel is best and wider is better than thicker. Some large washers are galvanised to go on roofs. To use these you will have to file off the coating and probably use some extra plumbers flux to get a good soldered connection. The picture shows the wire screen attached in two places, this is really to ensure a good electrical connection which is essential.

JULY 2012 - MORE DETAILS SOON

p.s. For heaven's sake put something on the top end of the wire (a blob of hot melt glue perhaps) so you don't stick it in your eye!

p.p.s. Our local 3 transmitter went off the air last week and I used one of these aerials to connect to a base station that is 5 or 6 miles away. I got 2/3 bars with the aerial connected and no bars without. In fact I had to connect the aerial before the dongle would fully connect. So the design does work!

SUITABLE CABLE FOR SALE
I have managed to get hold of a small quantity of thin low loss RF cable which works up to about 2.2GHz so very suitable for use with a 3G aerial.
To help new builders I am able to supply it in 1 metre lengths to the UK for £1.50 plus £1 p&p in the UK only.
Overseas would have to be by special negotiation for postage.
Payment by PayPal ONLY. Please email if interested and I'll send you the address..
p.s. I am not a business and only have a few metres spare anyway so I can't supply large quantities at this price.

 

3G Boosters

These are electronic devices that, believe it or not(!), amplify or boost the signals down from the mobile base station and then boost your data before it is sent back up. It's quite difficult to make a suitable unit from scratch, but much easier to modify existing devices such as those made for Wi-Fi to work at the adjacent 3G frequencies. We have tried modifying an amplifier sold for wireless internet  frequencies to the 2GHz frequencies used by 3G. This does work after a fashion but we are faced with the problems mentioned above of increasing the interference just as much as the wanted signals. It is perhaps for this reason that there seems to be a dearth of professionally made 3G boosters in this country. In the wide open spaces of the USA and Australia though it is a different story!

You can make a start and can easily get a femtocell amplifier for many mobile phone providers but that is not really what we are looking for on this web site. We are looking for a long term reliable broadband signal rather than occasional short term phone calls. We are working on the problem...

Home brew 3G software to make the best use of what signals you can get for example by combining two connections into one. When one goes down the other may well get better! I have one example running at present although it's not yet good enough to publish.

 

Easy way to boost 3G dongle signal that I have tried

(WORK IN PROGRESS JANUARY 2012)

I am now able to give one easy and practical suggestion of a way to boost the signal when using a 3G dongle.

You need an unused Sky type satellite dish although I have been experimenting with an old BSB dish which is smaller than your average Sky dish and this works well. One problem is that the larger the dish the more accurately it needs to be pointed so for this application smaller is sometimes better! To make this system work properly you must also know exactly where your 3G signal is coming from as you will be pushing all your signal in that one direction. Even a few degrees off beam will make you signals far worse than they are now.

Sky dishes are offset, that is they are designed with the focus off centre so you must point the dish far lower than normal. This may well involve modifications to the mounting clamp - more about this later. As you will be transmitting from the dish as well as receiving you should look for a dish that has a smooth surface with no obvious defects or dents. You can get hold of dishes that are solid rather than perforated - if you can then one of these is recommended. Remember though an unperforated dish will have a much higher wind resistance so will need fixing that much more securely. You will not want to be responsible if it falls on someone's head! If you are reading this abroad then a small c-band dish should be fine.

If you are using a dongle of the Huawei type, which is the make that I am most familiar with, then the most sensitive part is at the end furthest from the connector. I have found (rather surprisingly) that you get by far the best signal if you mount the dongle at an angle of 45°. Push the dongle through the ring that is normally used to mount the satellite L.N.B. which is not needed for this application. If using a different dongle then try mounting it upside, downside or inside out - try all directions!

Everything must of course be waterproof. I have placed my dongle in a small Tupperware type drinks container which happens to be the same diameter as the old L.N.B. Gaffer tape seals and holds it all in place for now while I experiment.

You must mount the dish reasonably close to the computer - certainly whilst setting the whole thing up - but it should never be more than 5 metres away. This is not a system where you can mount a dish on your roof and run a long wire down the wall, as you will certainly lose more signal than you gain, To get the signal to and from the computer I recommend that you use a 5 metre amplified USB extension cable which can be bought for £10 - £15 in the U.K. As you are transmitting you need as much voltage as possible to reach the dish, so an ordinary 2 metre extension lead should be avoided.

By the way if it is essential there IS a way to get round the distance restriction mentioned above, but it involves turning the USB signal into a network IP signal with an adapter at each end as well as providing a mains power supply near the dish. Expensive and a fiddle, but I suppose do-able if you must.

I get between 0 and 1 bar with the dongle hanging in the air and a full 5 bars signal when properly mounted in a well sited dish. This system really can make an enormous difference perhaps when travelling (although you would need a map of the nearby transmitters). One rule still applies that is that whilst you will probably not be able to get a line of sight signal you really still need to avoid walls, thick foliage etc. These things still attenuate the signal whether the dongle is inside a dish or not!

A quick look at the diagrams (which I hope to have ready very soon) will help make everything clear.

Oh a quick p.s. For some reason this scheme does not seem to work well when using the Mi-Fi type of adapters that include a built in wi-fi connector. I have absolutely no idea why this might be although it may be that these units are not made as sensitive as the normal Huawei dongle. Pity as I find my Mi-Fi invaluable when out and about.

Please do get in touch if you need more help.

LOTS and lots more to come including some hard details, plans and hopefully some details of when you can get suitable parts cheaply. Please look back. Always pleased to hear from you.

Rob.

p.s. There is a video on YouTube showing a booster that uses a saucepan. This quite simply does not work and I can't see how it might work - unless the signal is coming from directly above! There are many videos on YouTube that are complete cons - don't fall for 'em!

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