Bluetooth antenna?

[sojourner]

There has been some chatter on the forum about cheap bluetooth cards being available. I bought a card but would like clarification on antenna choice.

Some have written saying we can use the WIFI AUX antenna for BT. Although WIFI reception might be compromised, it generally is not much and turning the lappie a little (moving it around a little) generally resolves the problem.

Others have written about buying an Hitachi 4" long antenna and simply tucking the antenna by the BT card. Reception for BT is supposed to be good with this antenna.

Question is:
Which setup is really better? Has anyone tried switching between the two (Hitachi vs TP's built-in AUX antenna)?

[aaa]

I wouldn't feel like moving my laptop around to improve reception, so I'd prefer the dedicated antenna solution. You kinda hit the nail on the head with the tradeoffs of each arrangement. Bluetooth performance isn't what I'd be worried about, as either way it works.

[Johan]

I would certainly believe that the AUX antenna could be used for Bluetooth as well as for WLAN (a/)b/g. WLAN b/g are using the frequency range between 2410-2485 MHz (a number of "channels" are allocated in this spectrum; some are allowed in the US, some in the EU, some in Japan etc), while Bluetooth uses 2400-2485 MHz, again with different specific frequency allocation in different parts of the World. WLAN 802.11a uses frequencies around 5 GHz. Because of this "frequency co-location" the (b/g) WLAN antennas may be used for Bluetooth as well.

The two WLAN antennas in e.g. a T41 are identical - see for yourself in the Hardware Maintenance Manual - ThinkPad T40, T40p, T41, T41p, T42, T42p, and therefore they (one of them!) can be used as a Bluetooth antenna. If you however use one of them for Bluetooth, you may loose some amount of WLAN performance, since you by this loose the advantage of the "space diversity" by having, two physically spaced apart antennas: If one antenna does not perform well in a given environment (owing to e.g. the lid shading towards the WLAN router/access point), then the other WLAN antenna will statistically perform better... so the dual-channel "diversity receiver" simply continually switches between these antennas. This is discussed in the thread T40 wireless (Cisco PCI) keeps shutting down Wifi router (see the post of Wed Aug 01, 2007 7:04 am), along with other issues also affecting WLAN and Bluetooth performance (polarization etc.)

If you want to know more about the Hitachi antennas in ThinkPad's, see the thread Have I BT antenna in my system?.

Best regards,

Johan