Cable antenna » History » Version 15
laforge, 02/21/2016 11:23 AM
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3 | 15 | laforge | h1. The Cable Antenna: |
4 | 13 | dexter | |
5 | 1 | dexter | The antenna that has been shipped with the BS11 is a so called sector-antenna. That means it is designed not to cover only a part of the area around the BTS. And it has a gain. The gain comes from the signal that is bundeled and sent into the sector. The advantage: You can use several BTSs to cover a cell (Each cell sector has its own BTS ==> More calls) and you can cover more distance with less power. |
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7 | 5 | dexter | What is good if you want to run a mobile network is bad for experimental proposes. For us an antenna that covers the area around the BTS with a nondirected signal (like a donut) is perfect - so lets build one. |
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9 | Note: I have Adaptors that adapt the BS11 N-Connectors to BNC. Because BNC is my favourite connector type so the most of my homebrew radio equipment / cables have BNC-Connectors. That is the reason why this howto relates to BNC-Connectors. Just use your favorite connector type or N-Connectors for the BS11 |
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12 | 15 | laforge | h2. Step by step |
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14 | 15 | laforge | h3. Materials: |
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16 | 14 | laforge | !cableAntenna_materials.JPG! |
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18 | 1 | dexter | The antenna is made out of a pice of old coax-cable (about 15-20cm length) and a BNC connector. To make it all looking good we add a pice of shrink tubing at the end. |
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21 | 15 | laforge | h3. Connector: |
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23 | 14 | laforge | !cableAntenna_bncplugconnected.JPG! |
24 | 1 | dexter | The first task to do is to connect the connector to the cable. I used a solderable BNC-Connector. If you have an old network cable you can cut off the and. The result is the same. |
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27 | 15 | laforge | h3. Isolation-removal: |
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29 | 14 | laforge | !cableAntenna_shieldcutoff.JPG! |
30 | 1 | dexter | Now cut of the isolation and remove the metall shield. |
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33 | 15 | laforge | h3. Lambda/4 cut: |
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35 | 14 | laforge | !cableAntenna_cutoff.JPG! |
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37 | 9 | dexter | Now the most important step has to be done. We need to part where the shield was removed to lambda/4 length. To calculate the length you can use the matlab/octave script listed below. It is very important that you know the scale factor for the cable that you use. I used H155 cable which has a scale factor of 0.79. |
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39 | 13 | dexter | <pre> |
40 | 8 | dexter | %Parameters: |
41 | c = 299792458%m/s (Speed of light in vacuum) |
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42 | 1 | dexter | v = 0.79 %Cable scale factor (The wave moves slower in the cable/metall) |
43 | 8 | dexter | f = 900000000 %Hz (GSM900) |
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45 | 1 | dexter | %Calculation |
46 | disp('Wavelength [m] is:'); |
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47 | l=(c*v)/f |
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48 | 8 | dexter | disp('Antenna length [m] (Lambda/4) is:'); |
49 | l4=l/4 |
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50 | 13 | dexter | </pre> |
51 | 1 | dexter | |
52 | In my case lambda/4 is about 6.57cm |
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55 | 15 | laforge | h3. Shrink-tubing: |
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57 | 1 | dexter | !cableAntenna_shrinktubing.JPG! |
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59 | 11 | dexter | Now simply add some shrinktubing to the cable. That makes it save to handle and industry grade looking. I recommend to do a final test with a multimeter to ensure that your antenna has no short circuits. |
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62 | 15 | laforge | h2. Closing remarks: |
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64 | 14 | laforge | !cableAntenna_hardatwork.JPG! |
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66 | 12 | dexter | I have tested the antenna with 2 BTS as RX-Antenna and TX-Antenna. It worked fine and we could not see any harmful effects to the BTS so far. But i must warn. Use it on your own risk! |