UMTS field and a homemade antenna at 2GHz

What I delayingly I have to go outside the city and stay there for a few days. Yes, there is and finally to move closer to nature conceived to fall. The Internet is not something that I want, he just needs to work. The network coverage of 3G in remote areas of our region is slowly improving, but the ideal of all even as far as China is very far away. Built-in antenna USB-of"whistles" work categorically unsatisfactory. So, I've started the habit of "kolhozah»…
 

Brief overview of the situation with 3G

The vast majority of ready 3G devices only work with their built-in antenna and no way to connect an external antenna do not have. Those who have such, first, the day the fire in the evening straighten you will not find, secondly, this connection in overwhelming majority of cases is unreliable and has poor characteristics in terms of attenuation/reflection of the signal and additional noise. The name pigtail ("pig tail"), the decision in respect of such adapter cables, very accurately describes the situation.
Quality of built-in antennas acceptable for the urban environment, where BSCI stumbles through a step. For marching conditions such conventionally-Omni-directional super-shortened antenna does not fit completely.
However, many 3G-modems, even have no visible connector for connecting an external antenna have a connection point for antenna on the Board, apparently for diagnostic purposes. Often at this point even soldered connector.
Without "surgery", thus, not necessary.

"Surgical intervention" in 3G modem

The modem can be anything. My choice fell on Huawei E1550, because this old thing has turned me from a mugger in the alley now you can buy with it for 100 rubles — not sorry to spoil. Details of his modifications are well on the Internet any popular search engine.
In the General case it is necessary:

• remove or disable the built-in antenna
• to find the diagnostic connection if it is already soldered connector to remove (good Hairdryer)
• solder to it a piece of suitable coaxial cable, not forgetting that this is still the microwave (braid soldered the two points on either side of the Central core, the configuration of the contacts on the Board provides for it).

Since the contact connection points are very close, like popular cable RK-50 or RG-58, of course, will not work. I personally eat it a piece of this cable washed the outside of the laptop — where he connected the Wi-Fi module with an antenna. Its diameter is less than 2mm, which is great for such manipulations with the modem.

That's what happened to me (photo on the background of the reflector described below, the antenna):

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In addition to everything else the modem has been "unlocked" so that it was possible to test various operators.
 

Why antenna Harchenko?Dipole or GP is weak. Wave channel and a log-periodic aerial in addition to the complexity of hand-made at these frequencies and, as a consequence, fragile, have a very narrow main lobe radiation pattern. In marching conditions just "aim" to the base station (BS) and securely fix such an antenna very difficult.
A compromise was found in the form of zigzag antenna Harchenko — that it was time to try it. Her main lobe of the chart is wide enough to not really bother with a target BS, wherein the antenna is quite simple to manufacture and has a relatively good gain (6..9dB).
 

Modification of Antonietta Kharchenko enough broadband, but at the same group of transmission frequencies "from MT to the BS" (1885..2025 MHz) and "from the BS to the MT" (2110..2200 MHz) UMTS spaced far enough. As I mentioned in the comments to the previous article, the BS almost always has enough power to "shout" to the mobile terminal but the mobile terminal (MT) power is not enough (especially USB-"whistle"). You can, of course, to manufacture the antenna, optimally working in the group of transmission frequencies "from MT to the BS" and be content with mid-priced technique, but I wanted to squeeze out of the technology maximum.
I learned that the antenna Harchenko can be made more broadband by including multiple vibrators of the antenna in parallel in the same plane at the point of "powering". However, the calculated sizes of these vibrators for UMTS frequency groups in "short arm" differed less than half a millimeter at a desired conductor width 0.8-0.9 mm. That is to post a "short shoulders", while maintaining the plane of the vibrator I is not possible.
I decided I will make "the rules" and see what happens. Hence, a certain negligence in the manufacture of the first versions of the antenna: I just don't believe that it is "off".

First drawn on paper version of the vibrator looked so:

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For the "small" circuit center frequency was chosen equal to 2145 MHz, for "large" — 2010 MHz.

These rocketaware it was decided to make of the existing foil fiberglass with subsequent abundant tinning.
 

Manufacturer trial orsiitaliani contours vibrator antenna was repeated on the PCB:

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This will cause a Holy fear in many students:

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However, I also haven't worked with a glass spring, because of lower intermediate stage:

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Generally, of course, it can be done though the famous Edding marker 404 in the presence of skill, but somehow I wanted to like this, the old fashioned warm tube napolcom.

First tried the method of etching copper in a solution of composition "Citric acid+Table salt+hydrogen Peroxide". First was the complexity of poor quality (blurry) gidroperita. What was the matter, I realized, leaving in the solution a couple of pills from a new package (damp tablets gidroperita swollen, scattered, granular sense of them; kosher tablets dense, have a clear shape and not crumble in your hands). Etched copper really quickly, accurately and extremely cheap.
Thinking now what to do with several kilograms of ferric chloride that is bought once a "reserve»…

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Ready vibrator after tinning:

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Solder. Yes, the legs are made of soft foam. I repeat: I do not believe that it is "off" and left space for maneuver in the form of "adjustable" distance between the vibrator and the reflector.

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As an assembly. USB connector Prilepin double-sided tape to the reflector. The reflector is inserted into the cut half of a plastic bottle — that was without hands.

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The results of the test trial

I almost threw everything in the trash not razoblachitelnye high pleased with the standard antenna the modem more than 83% are not shown.

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Speedtest is ambiguous, but that, apparently, the problem is not air (the test was repeated several times, each test server had their own "cockroaches»):

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(good speed bad ping)

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(not very speed, good ping)

Well, it is a city. On the nail you can catch, as they say. I had this antenna in the floor and even caught some echoes of the signal.

But now it is time to leave the city. Are in a wooden frame with a metal roof. Phones catch so — so, the Internet at speeds of GPRS. Catch the nearest BS.

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It would seem that sparse. But the Internet is there and he is UMTS (and he tried to be different with that antenna!) Let's try Speedtest…

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Just like this! Almost a megabit!

At this stage, I realized that the antenna in this configuration operates. You can start the protection from mechanical impact, dirt and moisture.
 

Preparation for Hiking slovesnaya I wanted to put the antenna in a specialized box for external wiring. However, comrade harmboy told me much more simple, cheap and durable solution: a plastic container for a microwave oven. Indeed, the polyethylene is more durable and certainly transparent to the frequencies of interest to us. In addition, these containers are available in almost any hardware store, and boxes with cable glands have to look specialized.
The disadvantage of this solution, kolhozah. But I was, as everyone already knew, not scary.

In order to finish the design, I didn't even need to return to the city. Almost all need for Assembly I found at the local General store, the rest (including the tool) I have a:

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To begin, I introduced the USB cable inside the container (had to cut it off and solder again, not to make a huge size hole):

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Then I put the soldering iron and took one of their favorite tools: glue "hot Chinese snot" glue gun. Seal the cable entry:

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Fasten the antenna inside, we catch drops of glue critical places, so that nothing is hanging out when you carry:

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Filler two ugly heaps very neat feet below the antenna you can put on more or less level surface:

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After all these exercises antenna, of course, works still, because the radio part, nothing has changed, but USB is a "real soulless figure," which is to lengthen and solder a much easier and safer. The next step is to attempt to raise it in the attic or on a mast where the TV antenna is hanging now, but it's Friday night and I'm too lazy to do it, especially in this weather. Better turn it on, pour the rest of the photos of the device and will add atut short article.

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(vaguely like some kind of brand router) published

 

P. S. And remember, only by changing their consumption — together we change the world! ©

Source: habrahabr.ru/post/257357/