Dongle-icious!

[daftlad]

Putting a 3G dongle on a USB extension should not affect the signal quality as the connection from computer to dongle is digital (USB).  Unless the dongle uses the USB cable as part of the antenna, but that would be odd.

I am not sure why but I have a couple of devices that don't like USB extentions, I assumed it was something to do with the power? I really should put the meter on it to see what the resistance is.
Those cantenna things look fun, I assume they would work for mobile broadband as well as wi fi because the frequencies are similar? This is the site that I found most intresting.
http://www.turnpoint.net/wireless/cantennahowto.html
ta ta

[greg]

I know what you mean....

Have you tired different extension cables or a different USB port on the puter?  A good connection is usefull!  The USB connector is designed for repeated use, but does often not give a "good" physical connection.  Sometimes either end of the USB connector looks ok but is actually rubbish.  I am not advocating going and buying expensive gold plated super cables.

Some are better than others, and some USB devices are more sensitive than others.

[Justme]

This is the router I use

http://www.billion.uk.com/product/3g/7402gxl.htm

& the antenna was similar to THIS But with a higher dba gain

[EccentricAnomaly]

If the signal is weak the longer cable will  weaken the signal.

I agree with greg's reply: weak mobile signals and problems with the USB connection would be two separate issues.  A poor USB connection will not be likely to make a weak mobile signal worse. 

USB is all a bit magic with respect to cable lengths; for reasons I don't understand the higher speed versions work over longer lengths but, as I understand it, it all gets a bit critical with respect the capacitance of the cable causing the bits to get rounded off so the length limits will depend on the quality of the cable and how well implemented the drivers at each end are.

Those cantenna things look fun, I assume they would work for mobile broadband as well as wi fi because the frequencies are similar?

Yes, mobile broadband is around 1.8 GHz whereas WiFi is on 2.4 GHz so the dimensions of mobile broadband would be slightly larger (longer wavelength).  I'm not sure that the cantenna is necessarily the best thing to use as it relies on you being able to break out the aerial - something it's fairly easy to arrange with WiFi but not the sort of thing mobile phone companies exactly go out of their way to encourage.

An alternative might be Wok-Fi (wikipedia): use of existing sealed USB dongles (WiFi dongles or, I assume, mobile broadband ones) at the prime focus of Chinese cooking implements.

Slightly off-topic: something that's got my attention at the moment is the Tegola project, long distance WiFi links across the Sound of Sleat providing broadband access along the south coast of Skye and on the Knoydart peninsular.

[daftlad]

Yes, mobile broadband is around 1.8 GHz whereas WiFi is on 2.4 GHz so the dimensions of mobile broadband would be slightly larger (longer wavelength).  I'm not sure that the cantenna is necessarily the best thing to use as it relies on you being able to break out the aerial - something it's fairly easy to arrange with WiFi but not the sort of thing mobile phone companies exactly go out of their way to encourage.

I am not sure what you man by "break out the aeriel", do you mean making a physical connection into the dongle because some dongles have tiny aeriel sockets under covers on them.
I read on another forum tha the frequencies were.

2110-2125 3
2125-2135 o2
2135-2150 voda
2150-2160 t-mobile
2160-2170 orange

I do like the look of wokifi as well, I saw a you tube of a fella drop a dongle in a pan and the signal shot up.
ta ta

[breezy]

EA is on the money.

The 5m limit on USB is nominal (it's embodied in the standards, but in real life tends to be hit and miss). Good quality cables are the key.

Messing around with woks is an interesting way to pass the time, and ready-made off-the-shelf prime focus dishes are relatively cheap. You could even press a domestic DBA dish (e.g. Sky dish) into service (by mounting it upside down). Getting the dongle at the focus will require a lot of trial and error; patience in abundance will be required, and, since the signal is a digital service, you will have little in the way of indications to help you with alignment (unless you have access to some very expensive test equipment). Cassegrain feed dishes are also an option, but are less commonly available for consumer-grade equipment, so prices tend to be higher as a consequence.

Far easier to build, use, and align would be a simple corner reflector http://www.freeantennas.com/projects/Ez-10/ . A simple folded sheet of aluminium (or better, copper or brass sheet) is more or less all that is required. Even better, would be a 3D corner reflector http://www.qsl.net/yu1aw/3d_corner_reflector_antenna.htm

(n.b. Both of these links refer to antennae dimensioned for 2.4GHz, they would need to be scaled for the 3G band)

The Pringles cantenna is nothing more than a gimmick. It's an attempt to turn a cardboard tube lined with alu foil into a useful waveguide antenna. It would be easier (and far more effective) to build a waveguide from scratch using the correct (cheap) materials.

[EccentricAnomaly]

I am not sure what you man by "break out the aeriel", do you mean making a physical connection into the dongle because some dongles have tiny aeriel sockets under covers on them.

Yes, that's what I mean.  None of the WiFi USB dongles I've met have aerial sockets and mobile phones these days don't so I was rather jumping to conclusions that most broadband dongles wouldn't too.  If some do that's handy to know.

I read on another forum tha the frequencies were.

2110-2125 3
2125-2135 o2
2135-2150 voda
2150-2160 t-mobile
2160-2170 orange

Again, useful to know, thanks.  Even closer to WiFi frequences.  Presumably it's the 2G connections that are around 1.8 GHz.

Getting the dongle at the focus will require a lot of trial and error; patience in abundance will be required, and, since the signal is a digital service, you will have little in the way of indications to help you with alignment (unless you have access to some very expensive test equipment).

You could find the focus position using a WiFi dongle.  Programs like kismet will give you signal strength in dB (with more precision than the "bars" indicators on simple network managers).  I wonder if anything does that for the 3G dongles, e.g., the billion router that Justme referenced would though its web interface.

[daftlad]

According to an advert on a popular auction site these dongles work with aeriels.

Our Antenna fits the following models:
HUAWEI E160G,
HUAWEI E160,
HUAWEI E160E,
HUAWEI E169,
HUAWEI E110,
HUAWEI E620,
HUAWEI E156G and
HUAWEI E600, E612, E618, E630, EC321, E612,E618, E620, E630, EC321.

It seems to me that you can get 15db gain aeriels for less than 30 quid, I can't really se the point in building a cantenna if you really need decent gain.
ta ta

[breezy]

You could find the focus position using a WiFi dongle.  Programs like kismet will give you signal strength in dB (with more precision than the "bars" indicators on simple network managers).  I wonder if anything does that for the 3G dongles, e.g., the billion router that Justme referenced would though its web interface.

That's true up to a point. Kismet interrogates the RSSI from the radio module, and in that respect it is no different to any other utility (or embedded feature of a larger application). The underlying link is still a digital one, so the "all or nothing" characteristics of this type of technology still prevail.

Correctly aligning a parabolic dish on a point-to-point terrestrial link (without the use of the correct test gear) is non-trivial. It is often possible, however, to get an effective, working link by trial and error given patience provided that the signal path is not too challenging.

Achieving correct focus and signal polarity by trial and error requires a lot of patience.

[breezy]

It seems to me that you can get 15db gain aeriels for less than 30 quid, I can't really se the point in building a cantenna if you really need decent gain.
ta ta

Be very wary of claimed gain figures. I've field tested quite a number of similar commercial antennae in the 2.4 and 5.8 GHz ISM bands, and very few live up to expectations. I'd go so far as to say that many of these manufacturers appear to have developed their own "over unity" scams.

Given the modest cost, you'd have little to lose by trying one. You'd have even less to lose by building one from cheap readily available materials.

Caveat Emptor, as my granny used to say.

[w0067814]

If I recall corrrectly the 5m limit on cable length for USB is inter-bit timing relationships rather than capacitance etc. It takes a certain amount of time for the signal to propagate down the cable (approx 66% speed of light, or 5ns per meter). it is a similar issues with repeaters - you can only hang 5 repeaters until you start breaking the timing relationships. 25m is the longest supported cable length.

Each repeater will take 100mA from the bus if it is bus powered. Thus having a repeater in the mix can prevent high power items from working - each item is allocated 100mA for "free" and then must request and be granted further power up to 500mA by the host computer. If a device requests the full 500mA and there is a repeater in the mix the total required power will be 600mA, which is above the 500mA limit per port, thus the negotiation will fail and the device not work. It is the same with bus powered hubs - mains powered ones are better choice.

With regards to antennae - there is no point in coupling a good antenna to your device with crappy coax cable - most are supplied with very lossy cable. The effective transmit power can be worked out by adding the values together - ie Transmit Power at Dongle + Antenna Gain - Cable Loss = Effective Transmit Power at Antenna. The same is true for reception.

Keep you Dongle to Antenna cable short (ie 10 or 20cm) unless you are at the USB cable limit - if you have no choice make sure that you have a decent coax cable and connectors!

[clivejo]

I found that strapping the dongle to an old satellite dish (insulation taped to where you attached the LNB) and pointing the dish to the nearest mast can give a huge increase in the signal and speed.  I must take a few photos next time I'm up in the roofspace!