Placement is the biggest single advantage. Anytime you add an antennae you will not be "boosting" the signal, only shaping it.
The perfect antenna is a zero mass point in space and it's signal area is a perfect sphere.
Take the type of antennae that came with your DIR-655 or the antennae on the ANT24-0230, imagine a torus shaped zone around the antenna, this torus is your signal area. With dipole omnidirectional antennae (which both of these antennae are) the shape you get will always be a torus with little to no signal in the axis the antenna is pointing. Gain is a measurement of how much this area is distorted into a torus as opposed to a sphere.
Additionally there are 3 more issues at hand
One is that the cable leading to the antenna is technically an antenna itself and will not only have associated losses due to resistance but it's own signal area. This is why we suggest using the original antennae if your environment will allow it.
One is that if your antenna and your receiver have different impedance then you will create a standing wave which will cause even greater losses, this is the prime reason we will always suggest using a D-Link antenna approved for your device.
The last is that since we have 3 antennae here we are technically working with a battery of antennae which will have a special and complex interaction, due not only to their own interfering signal areas, but due to the actual signaling technology of draft N (which is written to take advantage of having this battery configuration). This is why we always ask the position your antennae are in and why we strongly suggest getting a battery of antennae (such as the ANT24-0230), as it is shaped to take advantage of these harmonics.
I hope that helped.
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Topic: Dir-655 upgradeable antennas? (Read 34644 times)