The Wi-Spy DBx uses a dual band antenna which covers the 2.4GHz and 5GHz band. The Wi-Spy 2.4x does not use the same antenna.
If you are looking for a good directional antenna please check out a forum post dedicated to good directional antennas that have worked for other customers: Wi-Spy Forum
The way Chanalyzer displays the data depends on many factors. Basically the Topographic view displays how often a certain point is being populated. Here are a few variables:
The Wi-Spy scans and sends all of the RF traffic it captures to a computer where the bundled software Chanalyzer, displays it in a readable format. As soon as you turn on the Wi-Spy 2.4x you'll get a colorful graph giving you a better understanding of your wireless surrounding.
The changes in color represent the radio activity around you. The brighter, red colors show the most traffic. The darker areas represent clear frequencies for your WiFi access point. It is that easy!
inSSIDer is a simple but powerful software tool that detects available wireless networks. When used on a laptop, inSSIDer can help determine where weak spots in the WLAN could possibly be. It is a great program to use with Chanalyzer.
The new native Wi-Fi API allowed Metageek to easily integrate the AP MAC address, and channel, which limits inSSIDer's software compatibility to Windows Vista and partial functionality in XP.
The Wi-Spy is a small spectrum analyzer that will show all activity on the 900MHz, 2.4GHz, or 5GHz spectrum. Using a Wi-Spy you can troubleshoot WiFi, Cordless Phones, Microwaves, Zigbee, Radio, Bluetooth, and many more devices. Seeing these devices will help you locate and identify interference.