Updated 4/25/2009: Added WET610N memory details
Updated 4/24/2009: Added WRT400N details
News of Cisco's WRT400N less-expensive follow-on to its WRT610N simultaneous dual-band draft 802.11n router leaked out shortly after CES. But with today's announcement, we are free to take a look inside it as well as the WRT320N dual-band single radio router and WET610N dual-band bridge that were also debuted.
The 400N doesn't look much different than the 610N, coming in the same UFO case with internal antennas.
Figure 1: Linksys WRT400N Simultaneous Dual-N Band Wireless-N Router
Figures 2 and 3 show the inside of the 400N and 610N respectively. Cisco has been pretty faithful to its main wireless technology supplier, Broadcom, only occasionally straying to other vendors. Figure 2 shows that the 400N is one of those cases, since it uses an all-Atheros design.
You never know with FCC photos how closely they match production product. I'm guessing that one of the RF shields has been removed over the upper radio and possibly a second over the processor and switch section. There is no sign of heatsinks, however. Note that there are two antennas per radio vs. the 610N's three per.
Figure 2: WRT400N inside view
Figure 3 shows the WRT610NV1 for reference, so that you can see the design,which uses a BCM4705 CPU, two BCM4322 single-chip dual-band draft 11n radios and probably a Broadcom BCM5397 5 port gigabit switch under the heatsink.
Figure 2: WRT610NV1 board
Figure 4 is a closeup of the WRT400N board, which is still a bit fuzzy to make out components. Fortunately there are more pictures in the FCC ID document, which clearly show an AR7161 600 MHz Wireless Network Processing Unit (WNPU) and dual-band AR9220 and single-band AR9223 single-chip draft 11n radios. There are no close-ups of the switch section. But since Atheros is relatively new to making switches, it's probably an AR8216 6-port 10/100.
I opened the review sample and confirmed the AR8216 as the switch and found 32 MB of RAM and 8 MB of flash. The 5 GHz radiio had a shield over it, but the 2.4 GHz did not. There were no heatsinks used on any of the devices.
The each radio has two antennas, sited at the four corners. Each radio's antenna pair is arranged diagonally, with the 2.4 GHz at the front left and rear right and 5 GHz at front right and rear left locations.