Homemade 3G Booster Antenna

Marc Fraser, Camp Hill, QLD, Australia

Homemade 3G Booster Antenna

I noticed a request on page 106 in Ask SILICON CHIP, November 2009 (from M. P. via email) “wondering if you guys have been able to come up with a home-made 3G Booster Antenna for use in homes that do not have the best 3G coverage”.

My daughter had this problem at her house near Beenleigh 40km south of Brisbane where, due to terrain shielding, reception on a Bigpond MAXON Model BP3-EXT 3G modem was marginal at best. 3G was their only alternative to dial-up - ADSL is not available.

Rather than an active 3G booster, I made an “external” antenna which could be sat on a desk near a window facing towards the edge of the hill which blocked the radio path. To minimise size, I used a bi-quad design cut for 850MHz. This feeds the primary SMA antenna socket of the modem via 4m of RG58U cable. Gain is about 11 dB.

The improvement was spectacular. Performance went from slow with frequent dropouts to top speed with consistently high signal strength indication. With a 353 x 90mm footprint and being just 353mm high, it is small enough to sit unobtrusively at the back of the computer desk, looking happily out the window.

Material for the backplane might be a problem for some constructors. I just happened to have a piece of 1.8mm aluminium sheet recovered from some computer equipment but any sort of sheet metal would suffice. The backplane is 353 x 353mm with 88mm flanges bent forward at right angles at the top and bottom to form a shallow U-shape, ie, the blank size is 532 x 353mm, allowing for bending.

The antenna is bent from a length of 2.1mm diameter copper wire with quad sides 86.1mm long and it is mounted 44mm in front of the backplane using apiece of hard plastic tube. The coax shield and inner conductor are soldered directly to the bi-quad feed points and the cable run back through the mounting tube.

The antenna wire was formed by bending it around two 2-inch nails (outside spacing 84mm) driven into a piece of timber.

Silicon Chip, 2009, №12