ASUS PCE-AC66 Wireless 802.11ac PCIe Adapter Detailed Features
Once the large heatsink covering the PCE-AC66 is removed, it’s easy to see that the heat is being generated in two very distinct locations. The large chip at the end of the board is the star of the show here – the 802.11ac “radio”, sourced from Broadcom. Covering almost half of the board’s real estate below the heatsink is an aluminum RF shield, commonly called a “can”, because it completely encloses a section of the active circuitry. If you’ve ever ripped apart an old cell phone, you’ll be familiar with the construction details of these shields. It’s impossible to see any details of the circuitry through the RF shielding cans, and they are just as impossible to disassemble without destroying them. Thankfully, the FCC has generously shared the photos of their full tear-down with the world, and I’ll show you what’s inside later. Two things strike me, looking at the partially disassembled board. One, the gentle curve of the PC traces connecting the BCM4360 to the RF power amps that are hidden underneath the shield. RF signals don’t like making sharp corners, and when they do, RF leakage is a common side effect. Secondly, the thermal package here is seriously compromised by the monstrously thick thermal pad sitting between the BCM4360 and the heatsink. Clearly, the RF power amps are getting the lion’s share of benefit from that big red heatsink.
The BCM4360 Wi-Fi chip sits at the top of their “Fifth Generation” line of Wi-Fi devices. This IC is one of the things that set this PCIe Adapter apart from the pack, by generating the three 802.11ac data streams that give you that massive 1.3Gbps maximum data rate. The BCM4360, contains a number of performance enhancing features, including:
- Support for 80MHz channel bandwidth, twice as wide as current 802.11n devices
- 256-QAM, a higher modulation scheme that increases data transfer efficiency
- Standardized Beam-Forming technology that helps increase wireless range, penetration, and data rates
- Support for Low Density Parity Check Codes (LDPC) and Space-Time Block Codes (STBC)
Once the RF shielding can is removed, all of the basic functional blocks are revealed. On the left are the two RF power amplifiers for the 2.4GHz and 5GHz bands, and their associated support devices. With the heatsink and shield in place, the signal flow wasn’t completely clear, but you can now see how each RF section of the board feeds the three separate antennas. The component layouts at each of the three antenna pickup points show the two RF signals being pumped into each antenna, one in the 2.4GHz band and one in the 5GHz band. Each of the three data streams are isolated from one another electrically, and with solid metal partitions in the RF shielding. Overall, it’s a clean, tidy design layout, and is on par with the mature design that I saw in the companion ASUS RT-AC66U 802.11ac wireless router that I reviewed last month. The picture below is courtesy of the FCC, and I apologize for the quality of the image. However, I certainly appreciate the fact that I don’t have to destroy the review sample, just to get a peek at the high tech chips inside. Trust me; it’s almost impossible to get those aluminum lids off without destroying them, and usually something else on the board gets trashed at the same time.
The antenna base that is included with the PCE-AC66 card does double duty as both a movable platform for the three antennas, and as an extension cable. Three SMA connectors are built into the triangular plastic stand at each of the corners. It’s very convenient and easy to switch the antennas from the back of the PCIe card to the antenna base, and vice versa. The connectors are well made and screw on and off easily and reliably. Everything that needs to be is gold plated, so there’s no worry about corrosion, which would definitely be a problem with the small voltages involved with these RF signals. Remember, at this point in the signal chain, you’re just talking about whatever voltage is developed by radio waves hitting a piece of wire.
The other end of the antenna base (electrically, anyway) is populated by three female SMA connectors which screw onto their counterparts on the back of the PCIe card. In order to achieve the benefits of a remote antenna setup, it’s important that the cables and connectors be of high quality. Otherwise, the signal losses involved end up throwing away all the gains you made by locating the antenna in the best possible spot for clear reception. I definitely saw improvements in data rates when I optimized the locations of the router and adapter antennas, during my testing. Since the router and the PC that this PCIe adapter is going to sit in are probably going to stay in one place, it’s worth your while to get the antennas set up in the best possible location and orientation.
The easiest way to optimize the antennas at the PC end of the connection is to use the utility software that ASUS includes with the PCE-AC66 802.11ac Wi-Fi adapter. Both the Signal Strength measurement and the Data Rate measurement tell their part of the story. The signal strength value changes more rapidly (the refresh rate is set in software…) and is most useful when trying different antenna locations or orientations. Just for reference, the signal strength is measured with a specialized form of the decibel scale. dBm is a unit of measurement for the power of radio frequency signals, using the signal voltage and the load impedance. The dBm scale is logarithmic, and it’s based on a reference magnitude of zero dBm = 0.001 Watt. BTW, the “B” in dBm is supposed to be capitalized, in honor of Alexander Graham Bell, who the measurement scale is named after. The strongest signal I got in my testing was -24dBm, which is 4.0 microwatts. You can see from the screenshot below that I only needed -28dBm (1.6 microwatts) to achieve the maximum data rate of 1300 Mbps on the 5GHz band.
Let’s take a look at the Features and Specifications of the PCE-AC66 Wi-Fi adapter next. It’s a fairly simple device, so it won’t take us long to review them.