Aerials for 900MHz

External aerials for mobile phone

A necessity to be on the phone whole day appeared at me. Unfortunately there is no reliable GSM coverage in the place I spend time. There is huge amount of external aerials on the market. This aerials are not cheap and don´t guarantee reliable signal. DIYer´s soul does not know other solution than to build aerial by itself.
The most simple are aerial ?? rod - prutové???. Its disadvantage is low gain, about 3-5dB.


1/4 lambda
For the less pretentious use you can try "one quarter" ground plane. Arms of the aerial are 1/4lambda (wave length) long i.e. 8.32cm. Function of the aerial is not influenced by exact dimensions and impedance matches coaxial cable and mobile phone ( 50ohm).




5/8 lambda
Aerial 5/8 lambda offers the highest gain ( cca 3dB) . That´s why I started with this one. It is soldered of copper wire on small board. Aerial has non-resonating lenght. You have to tune it up (by changing legth of the reel) to the lowest SWR. Hf part of mobile phone is designed to drive very exotic loads and should be able to work with this aerial. If you don´t have SWR meter in your property you can build simple one .
I was very pleased with this aerial. Using Nokia 5110 with activated Netmonitor I can measure gain about 3dB. Expenditures almost nothing ( only Cu wire) and time cca 1/2 hour.


Yagi
The Yagi aerial offers much higher gain- about 10-15dB. This allows to use aerial with longer cable ( loss for RG58 is -0.55dB/m). There are programs for design of Yagi aerials on the net. I decided for proved construction. One of solutions uses folded dipole. I preferred more compact solution of R. Gesrstendorfa with open dipole, published in Elector 4/99. Download 449kB pdf.
There is only one problem. With balun. Recommended "flat UHF cable" is not avaible. So I made balun from 50ohm coaxial cable, common construction ( 1/3 + 1//4 lambda noose). I measured gain about 10-13dB on the end of 4m cable (RG58).




Device for mobile telephony working

10.8.2003
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