[Asus  Eee Pad Transformer Prime] compuw22c:
So I realize this thread is mainly about opening and hard-modding the case to resolve GPS/WIFI issues. My wifi is/has been ok, however my GPS has been problematic from day 1. Yes I can get a lock, but never passes the driving test. In addition, it's very strange how I can achieve, INDOORS, 12 satellite locks many in the 20's for SNR, then without moving an inch loose all signal. Then I came across this post (related to the SGS1, though I do believe it's fairly universal to all phone/tablet GPS receivers. I know it was mentioned somewhere before but, in my mind it's very possible the issue lies in the agc control in software.

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"That's pretty much what I'm seeing now..certainly the SNR values being much better and more stable when the phone is off and it's acquiring locks..and that noticeable increase in performance continues when you turn the wireless back on. It does give me some possible ideas as to what the issue might be. I can't seem to find the exact chip they are using in this phone to look at a datasheet or programmers guide.. seems it might be one of three..but they're all a similar architecture. One common thing you have to do with the host processor assisted type designs that are being widely used now is control, via a Java or direct API, the tracking of the satellite signal being received and the initiation of the AGC or Auto Gain Control circuits. Basically a teeny weeny signal from the satellite comes in to the GPS device at say 50 millivolts, and to bring it in optimum peak range of the decoding circuits, let's say 0 to 1.8V you apply gain or amplification to the signal until it nicely fits in this range, so you get a good look at it. If you start this gain adjustment process in the presence of noise spikes greater than the signal you want to receive then the gain is set incorrectly for the intermittent noise rather than the required signal and there isn't enough amplification to reliably digitise and quantitise the required signal. Conversley if you set the AGC tracking whilst the noise is completely absent then it ramps up the gain and when the noise does appear intermittently at a higher level and is amplified it hits the limits (the 1.8V say) and gets clipped, causing all sorts of nasty harmonics and distortion.. and a sudden whacking change in SNR. It's all actually a bit more complicated than that but that's the basic principle. These AGC circuits are, as the name implies, automatic and they try and track changes in signal level to dynamically adjust the gain. So they don't do this at the slightest tiny pulse they have a programmable hysteresis or delay so it keeps a decent average value. Problem is they need something generally representative in the first place to get a coarse lock before they can get a fine one and a dirty great spike while it's setting up, say from a mobile phone transmitter, could mess that up. All mobile phone modules, even if they aren't being used for voice or data at the time, perform periodic 'local area updates' where they send a short burst of information to the cell so that the network knows whether it's still attached and still on the same cell. This sudden transmit burst also suddenly ramps up the power consumption. In a good design a high capacity capacitor (or super cap) is used to provide this short-term peak power demand and the effect on the rest of the power rail is minimal..in a bad one it causes a sudden huge increase in load across the whole power rail and often noise on the rest of the system. So..do other users see significant average SNR changes and better locks after first tracking with wireless off (i.e. in flight mode) ? Would be very interesting if that's a common observation and would indeed point to intermittent locally generated noise and something like incorrect AGC tracking as a root cause. Might even be fixable in the driver if they change the start point/duration/sampling interval on the AGC ..or even make sure the phone isn't transmitting noise at the time it performs the initial AGC lock. Might also explain why some users get good GPS performance and some don't..they're just lucky when it sets up the AGC. Can we get a straw poll of the efect from other users with GPS problems?"

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I'm glad to see you guys achieving some pretty amazing results, as well as gaining some great new info for the community. I also haven't ruled out modding mine myself, but for now at least I'm hoping someone much smarter than me can figure out a) if the agc is enabled and/or working/crashing and b) if we can fix (or possibly just transplant from another device with the same gps chip) the existing drivers. It's possible that your mod is working because let's face it, you guys now have antennas that are larger and better than most laptops :P This may make the agc completely unnecessary because of the immense strength of the signal, though it still may be possible to obtain SOMEWHAT acceptable (at least not these horribly inconsistent drops standing still) results without hard modding. LOVE all the pics and info though, and I certainly haven't ruled out hard-modding. My main concern right now is first the Wifi/BT dropout, second is GPS. Other than that, very happy with my prime and the fact that despite all the whining around here, we definitely have some very talented people on our side here at XDA :)