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Hi:

I have an AirMagnet handheld with the a Cisco Aironet 352 card with MMCX connectors.

I bought an 8dbi omni antenna and pigtail and connected it up to the AirMagnet.

I can normally see about 8-10 APs in my campus WLAN out of a total of about 30. I was expecting to be able to "hear" more APs that were further away, but the performance seems to be no different than with the built-in patch antenna in the Aironet card. The performance may even be slightly worse.

Is this expected behavior? I understand that an antenna is a passive device that can only detect a signal if it is there, but I would expect that one of those car-mountable 8dbi omnidirectional antennas would be better than an integrated NIC one.

well...

The antenna's that are built in to the card may be diversity antennas and thus creates a clearer signal with better stn ratio's and thus the ability to connect and negotiate faster transfer rates...

The 8dBi antenna you used, that was not diversity, but patch/omni...so this could lead to a "dirtier" signal being send and received but should increase your range at least x2 in terms(using the 3dB theory)...also using the antenna cable and anything else between you and the 8dBi antenna introduces loss...

If you switched over to 11g card w/external antenna's you may get better signals with OFDM being used in place of DSSS in the 2.4 Ghz arena in some situations...

What is your Horizontal and Vertical Beamwidth of the 8dBi antenna?
I like to think of a flashlight in the pitch black...the more you twist the head of the flashlight, the more narrow the beam gets as it focuses on another object in the room...
this is what's happening when you increase the dBi in realtion to the beamwidth of the antenna...the higher the dBi gets, the narrower the beamwidth gets...
Now, when you have another flashlight on the other side, how much if it's "beamwidth" is inline with your "beamwidth" and are there diversity beams being used...wooo (it's too early)
What I mean is, your beamwidth from the antenna has changed, and may not be traveling the same way throughout the campus and to the other receivers as the other antenna did.
How is your antenna mounted, in relation to how it was when the integrated antenna was used? Aligning antennas for optimal use and design is only half the battle though. First, figuring out what type of antenna to use...