Which 3rd antenna to install

[fj2fjr]

I will be upgrading my Inspiron 1521 PCI-e wifi card from a Dell-1390,two antenna to an Intel 4695 agn which needs three antennas. I have a pair of antennas that I believe are for the standard 2.4Ghz use, they are 75 cm and 98 cm in length and have a flag type antenna that is about 1 and a 1/4 inch square. Will either of these work and if so which lengh would be best? I tried to attached a pic of the type of antennas I have to use but, not sure how to post with pics so I hope it works.

 

[thiggins]

The other two antennas are for a WWAN card and designed for a different band. You can try them, but don't be suprised if they either don't work or reduce your performance.

 

[fj2fjr]

The other two antennas are for a WWAN card and designed for a different band. You can try them, but don't be suprised if they either don't work or reduce your performance.

OK, I was apparently sold a bill goods, $3 bucks wasted!
Would you know what type of third antenna I need and where to get one?

 

[thiggins]

I thought you were referring to antennas already installed in the laptop. I can't tell anything from that picture you posted. Post a link to the product page instead.

At any rate, where are you going to put the antenna? You don't really need the third antenna anyway. It won't make that much difference in performance, if any.

 

[fj2fjr]

I was goin to install the antenna behind the LCD. I already have the two factory installed antennas and I wanted to add a third one. I've read that many people have added a third antenna this way but not sure of the type used or needed. I thought you needed the third antenna to achieve dual band Tx Rx, if not, what is the third one used for?
P.S. I really appriciate your replies and I love this site. It's a GREAT place to obtain networking info.

 

[thiggins]

For dual-stream N radios (which includes the Intel 4695 ag), the third antenna is used only for receive. It has nothing to do with dual band operation.

802.11n relies on MIMO technology to deliver its high throughput. MIMO, in turn, depends on uncorrelated signals arriving at the receive antennas in order to support multiple data streams that provide the higher throughput. In other words, MIMO (and 11n) will provide higher throughput when signals bounce around more before they arrive at the antennas.

A third antenna just increases the probability of receiving uncorrelated signals. But so can moving or rotating the laptop, or the furniture in a room or many other factors. This old Atheros whitepaper might be a bit hard to follow for non-techies, but has more details.

Note that the Intel 4695 does not support 40 MHz channel bandwidth in the 2.4 GHz band. So you won't get a 300 Mbps link rate when using 2.4 GHz. But you will in 5 GHz.