Mobile Phone Antenna
   
 
Feb 6, 2005
 
Recently there are some sort of construction works going on near my office building. As the new structure goes taller, the reception of my mobile phone becomes weaker. In the past week my phone can barely pick up any signal at all. So time to find a solution. Luckly my Motorola E398 has a socket for external antenna. So I decided to give it a try. After googling the Internet, it seems that Motorola is not selling any 'official' antenna. And the third parties ones are not cheap either. So I decided to make one myself.
 
The Antenna
The antenna itself is not hard to get. I managed to find one that is good for the 900MHz range. Too bad that it does not support 1800MHz as my phone can do dual-band with my operator.

 
Connectors

Finding a way to connect the antenna to my phone is a little bit tricky. Needless to say, I cannot find any connector that can bridge my phone and the SMA connector on the antenna. And the biggest problem is I know nothing about working with BNC-type of cable! I also do not know how to connect the antenna probably (e.g. do i need to ground it somehow?)

Anyway, the connector on the antenna seems to be a male SMA connector. So I went to buy a female SMA connector and soldered a pin (ripped from a SMB connector) on the other end. The pin can be inserted to the socket on my phone. The combination works, just that the pin connection to the phone is not secure engouh, though. Need to find a better way later.

 
Performance
Testing the antenna with my Motorola E398 at my home seems to prove that the setup does work. The signal strength jumps from 2 to full when the antenna is connected.

To measure the real signal strength, I used the antenna with my old Nokia 6150 (which is hacked with the NetMonitor function.) The followings are noted:

  • RX to the current cell (channel 1) has boosted from -73dBm to -63dBm with antenna connected
  • The antenna supports 900MHz only. Without antenna, the second cell is the 1800MHz PCS channel 580. (For GSM 900, channel nubmers are 1-124. For GSM 1800, channel numbers are 512-885.) When antenna is connected, all the top three cells are 900MHz.

 
Cost

  Price (HKD) Price (USD)
Antenna $55 $7.05
SMA (F) square panel $20 $2.56
SMB (F) $18 $2.31
  Total: $93 $11.92

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