Does the external antenna for 3G modem which is not connected, but simply "put" on the modem?

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Always considered an absolute absurdity and a "joke of the authors of" every kind of antenna for 3G modem of type "cupping antenna" which is connected to the modem this way:
image

But just today I met with selling such a kit
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In which the modem is placed in a kind of "frame", which is connected to the antenna
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I'm not good at electronics, but I think the use of this approach in microwave technique some kind of perversion, and this method is at best not degrade the signal.

Please tell me whether this approach can give a signal gain for several dB? Or similar "factory" solution is nothing more than another Scam to get money?

PS I Have hands grow from the shoulders, I know the correct way to rework modems for external antenna in case of absence of the adapter, and can implement them. But I'm interested in commercial solutions. Adapters for the most popular modems in the sale I found, but the approach described above without altering the modem it seems to me some kind of nonsense
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3 Answers

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I method the tried — does not help.
\r
The surest way is to buy a USB extension cable and bring the modem to the street.
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Theoretically, if you take a piece of iron is strictly designed shape, positioning at a predetermined distance from the antenna, orienting correctly, it turns out the transformer on long lines — the item is used in microwave equipment. Part of the signal will be transmitted to an external antenna, but not 100% sure.
And if, as here, wire wound anyhow or a piece of sheet metal to be applied, the efficiency will be zero.
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Works, but with some luck.
We test exactly the same perechodnik, as in the last photo. He gives about minus 15 dB. Another 5-10 feet of cable will eat between 3-5 dB (if the cable is good) to 5-10 dB (if the cable is mid-priced)
\r
Personally, I was never able to achieve such perechodnik at least some stability.
If you do something non-contact, it is anyone need another active amplifier.
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