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

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

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)

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 and you will be pushing all your signal in that one direction. Even a few degrees off beam will make signals 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.