Sunday, November 20, 2005

Mobile Phone Antenna (Feb 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 is dual-band.


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.

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.


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.


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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