In our review of ASUS' Eee Pad Transformer Prime I mentioned that I couldn't sustain speeds greater than 2Mbps over WiFi on my review unit. In practice, most web pages loaded at a meager 0.5Mbps. ASUS insisted the problem was limited to my unit however CNet referred to a similar issue in their testing:

Unfortunately, during the review process, we experienced some very suspect performance issues (detailed below), which led us to believe we were possibly in possession of a faulty unit. So, we are going to hold off on giving final ratings for the Prime, but check out our initial impressions.
At the same time, I had test data from both ASUS and NVIDIA that show the Prime is capable of reasonable WiFi speeds. Yesterday morning I received a replacement Prime which was tested prior to being sent my way. The good news is the 2Mbps cap and poor range are both gone, the new sample is much faster on WiFi. Clearly there was something wrong with my original unit and it's being sent back to ASUS today for an autopsy. The bad news is I was still getting numbers around half of the original Transformer.
Using Ookla's web app I get a consistent 34 - 37Mbps on the original Eee Pad Transformer (our actual WiFi performance tests involve downloading a file from a local server, but Speedtest was a quick and easy way to verify the problem). My original Prime review sample averaged around 0.5Mbps, while the replacement Prime got around 10Mbps - all in the same test location. Fiddling around with location I could get the replacement Prime up to 16Mbps. My test area is riddled with challenging interference so I setup a separate test area in another room. Even after buying the same Netgear WNDR4500 wireless AP that ASUS verified 31Mbps+ operation on, I wasn't able to break 16Mbps.
I have four other APs covering my house, I turned all of the radios off as a last ditch effort. Boom - 36Mbps on the Prime.
The culprit appeared to be either my 3rd gen Time Capsule or 5th gen Airport Extreme, with those radios off and using the WNDR4500 I was able to get performance competitive to the original Transformer. Here's where things get interesting. The original Transformer was made out of plastic, through which RF travels quite nicely. The Prime's metal construction makes things a bit more finicky. Indeed this is exactly what I saw, where depending on tablet and AP orientation I'd see anywhere between 10Mbps and 36Mbps downstream (average speed tended to be in the 15 - 20Mbps range). Apple gets around this issue in the iPad by putting the WiFi antenna behind the plastic Apple logo, however it's not entirely clear to me where the WiFi antenna is on the Prime (I have this policy about not taking things apart until I'm done testing them).

As to why performance was lower with the Apple APs active, I'm not entirely sure. Chasing down RF interference issues can be a severe undertaking. One thing is for sure, the Prime is going to be far more finicky than its predecessor when it comes to reaching peak speeds over WiFi. 
WiFi performance isn't the only thing that improved with the new unit - I'm getting much better battery life as well. Our video playback battery life test doesn't have anything running in the background, but we are actively connected to a WiFi network throughout the duration of the test. As I surmized in our review, it's possible that whatever was causing the WiFi issues also had a negative impact on battery life. Curious to find out if battery life had changed as well as how the TF Prime did in its Balanced power mode, that's the first test I ran upon receiving the new review unit. Things are starting to look a lot better:

Video Playback - H.264 720p Base Profile (No B-Frames)

I'm running the new unit through the test in Normal mode as well, I'll have updated results there by the end of the weekend. Given the rush to get the initial review out, you can expect a followup (along with a video review) sometime next week. I'll be working on it as well as some HDD/SSD caching stuff all weekend.
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  • Anand Lal Shimpi - Friday, December 2, 2011 - link

    Of the available test data (which admittedly there isn't much) it would appear that my original unit wasn't behaving typically. I don't believe what I've been sent is cherry picked, but I do believe that ASUS may have an assembly line issue that it needs to pay attention to.

    More info as I get it...

    Take care,
  • mcnabney - Friday, December 2, 2011 - link

    Or the original unit was just even MORE incompatible with Apple wireless access points. You never indicated if you shut the other RF noise down while troubleshooting the first device.
  • Anand Lal Shimpi - Friday, December 2, 2011 - link

    When troubleshooting the first device I did indeed turn off the WiFi on my Apple APs and played around with a Netgear WNDR3700 I have in the basement - it did not fix the issue on the original unit.

    In my extended testing of the original Prime I discovered that it had *very* limited range, which points me in the direction of something being wrong with the antenna in that unit.

    The behavior of this unit is very different.

    Take care,
  • bh192012 - Friday, December 2, 2011 - link

    Did you at any point during any of your testing (original TF, prime 1 / 2 or iPad) turn off your neighbors wireless APs, cell phones, cordless phones and microwaves? Yes wireless troubleshooting really really is a PITA.
  • OCedHrt - Friday, December 2, 2011 - link

    Sounds like antenna connection/placement issues.
  • jramskov - Friday, December 2, 2011 - link

    Thanks for the update. It's great to see how Anandtech again and again goes further in their investigation to find the cause of the problems.

    This could be the one problem that makes this otherwise excellent product fail...
  • Anand Lal Shimpi - Friday, December 2, 2011 - link

    It's our job after all :)

    Thank you for reading the site :)

    Take care,
  • jramskov - Friday, December 2, 2011 - link

    Sure, but it is the job of many other sites as well and you seem to consistently go the extra kilometer (yes, I'm from Denmark - I don't use miles :p )
  • jramskov - Friday, December 2, 2011 - link

    And btw. do you agree that this issue might be what prevents it from being a "buy this, you'll be happy" device? (there's probably a better english term but whatever...)

    Not being a huge Apple fan I must say that generally they are able to create devices that fit that category. I would love to see a lot more devices that fit that category because competition is always good :)

    Keep up the good work!
  • dtham - Friday, December 2, 2011 - link

    I love how you provided an update and root cause analysis of the performance issues. Now that you know about the WiFi issue, are you going to be changing your test specifications (Eg. Building a Faraday cage or as you did, disable APs from the vicinity?)?

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