Cable antenna » History » Version 10
dexter, 02/19/2016 10:48 PM
1 | 1 | dexter | |
---|---|---|---|
2 | == The Cable Antenna == |
||
3 | |||
4 | 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. |
||
5 | |||
6 | 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. |
7 | 1 | dexter | |
8 | 6 | dexter | 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 |
9 | |||
10 | 5 | dexter | == Step by step == |
11 | 10 | dexter | ==== Materials: ==== |
12 | 1 | dexter | [[Image(cableAntenna_materials.JPG,width=300px)]] |
13 | |||
14 | 6 | 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. |
15 | 5 | dexter | |
16 | 10 | dexter | ==== Connector: ==== |
17 | 1 | dexter | [[Image(cableAntenna_bncplugconnected.JPG,width=300px)]] |
18 | |||
19 | 6 | 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. |
20 | |||
21 | 10 | dexter | ==== Isolation-removal: ==== |
22 | 6 | dexter | [[Image(cableAntenna_shieldcutoff.JPG,width=300px)]] |
23 | |||
24 | Now cut of the isolation and remove the metall shield. |
||
25 | 7 | dexter | |
26 | 10 | dexter | ==== Lambda/4 cut: ==== |
27 | 1 | dexter | [[Image(cableAntenna_cutoff.JPG,width=300px)]] |
28 | 8 | dexter | |
29 | 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. |
||
30 | |||
31 | 9 | dexter | {{{ |
32 | 8 | dexter | %Parameters: |
33 | c = 299792458%m/s (Speed of light in vacuum) |
||
34 | v = 0.79 %Cable scale factor (The wave moves slower in the cable/metall) |
||
35 | f = 900000000 %Hz (GSM900) |
||
36 | |||
37 | %Calculation |
||
38 | disp('Wavelength [m] is:'); |
||
39 | l=(c*v)/f |
||
40 | disp('Antenna length [m] (Lambda/4) is:'); |
||
41 | 1 | dexter | l4=l/4 |
42 | 9 | dexter | }}} |
43 | |||
44 | In my case lambda/4 is about 6.57cm |
||
45 | 10 | dexter | |
46 | ==== Shrink-tubing: ==== |
||
47 | [[Image(cableAntenna_shrinktubing.JPG,width=300px)]] |
||
48 | |||
49 | Now simply add some shrinktubing to the cable. That makes it save to handle and industry grade looking. |