The Metal Frame & External Antenna with Dynamic Tuning

While I’ve discussed material choices before in the context of mobile devices, the new Moto X requires a new depth of understanding in order to really appreciate the amount of work Motorola has done to enable the industrial and material design desired. In order to avoid issues with the metal frame detuning internal antennas and maintain radio performance, Motorola has developed their own custom antenna tuner that is supposed to be even better than the QFE15xx antenna tuner that Qualcomm has made as a part of their RF360 package.

Of course, at this point the iPhone 4’s “death grip” issue has been discussed to death. In short, due to a lack of antenna diversity, it was possible to easily detune the phone’s antenna and significantly decrease signal reception by putting a finger on the gap between two parts of the metal frame. Understanding how an antenna tuner can help to resolve this situation requires an understanding of impedance and how it relates to antennas.

The first and inevitable question is what impedance is. To briefly summarize this topic, impedance is essentially resistance in an AC circuit. Impedance in an AC (alternating current, or what comes out of most power outlets) is determined by resistors, capacitors, and inductors present in the circuit. In antennas, what’s really happening is that electromagnetic waves in the air are causing the antenna to resonate, and as a result the waves are converted in electrical signals. While this is easy enough to understand, the crucial portion of this is where the antenna connects to the rest of the system. Antennas inherently have an impedance determined by natural resonant frequencies, the height above the ground, and the conductors used to construct the antenna. For the most part though, this is relatively easy to tune for at the factory such that the impedance mismatch is small.

The major problem is that the real world is not just the inside of a factory. As mentioned before, the hand detunes the antenna due to its capacitive effects. This means that the impedance changes. For those still following along with the physics, the reason why an impedance mismatch causes reception to worsen is because the electrical signal is still in the form of a wave in the AC circuit, parts of the wave will reflect just like how some light is reflected when crossing from one medium to another, which is why water can appear to be a mirror from one side but a window from another.

Now that we’ve gone over the physics, let’s get back to the Moto X. Motorola has developed their own custom antenna tuner. While Qualcomm has their own antenna tuner, the major differentiator is that this antenna tuner actually detects capacitance changes at the antenna and adjusts impedance accordingly. In practice, the antenna is retuned incredibly quickly, with next to no hesitation. Motorola demonstrated this by showing two Moto Xs that were identical except one had the antenna tuner disabled. The Moto X without this antenna tuner rapidly dropped from ~23 dBm output power to ~7 dBm output power. The unit with the antenna tuner managed to achieve around ~15 dBm output power after detuning. Remember, decibels are a logarithmic scale so this represents around a 6.3x increase in power output.

In addition, in discussions with Motorola’s engineering team they claimed that the new Moto X improves upon the receive sensitivity of the first Moto X. This is no small feat as the original Moto X was known to have some of the best radio reception amongst its peers. Once again, this makes sense as even though polycarbonate is RF transparent there will always be some level of reflection, just like how there is reflection with impedance mismatches, and I would once again refer to our article on materials in mobile devices to get a better understanding of this subject.

Introduction & The New Moto X Moto Voice, Display, Actions, Attentive Display, Sound, Camera, and Final Words
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  • erikiksaz - Friday, September 05, 2014 - link

    Now this is why I love anandtech. Sum up all the specs in a chart (instead of of a 5 min video parroting back all the specs), and educate me on all the aspects of the phone that other websites simply do not cover.

    Thanks for the great preview.

    Any more details on the color reproduction, sound quality/loudness of the speakers?
    Reply
  • JoshHo - Friday, September 05, 2014 - link

    The speakers are definitely quite good in quality, but I need to try some subjective comparisons and collect some data to really get a better idea of how sound quality is on the speaker. Reply
  • imaheadcase - Friday, September 05, 2014 - link

    The one thing i don't like on my moto x is the speakers, you can't sit it on a flat surface because they are on back and muffles sound. kind of annoying when you want to watch videos on lunch break. Reply
  • imaheadcase - Friday, September 05, 2014 - link

    Oic it HAS a front speaker? excellent news! Reply
  • craighamilton - Saturday, December 06, 2014 - link

    The Moto X is not very popular if you look at consumer based reviews (such as
    http://www.topreport.org/phones/ which is my favorite).
    Reply
  • JoJ - Monday, September 08, 2014 - link

    Hi Josh, I'm new to your phone reviews, though not to this site, thank you for many years of providing great reference everyone, especially also the commenters here..

    Is it possible to test phones' speaker abilities by just putting them in a not so huge anechoic chamber? DIY, but I know you'd do a decent job, and providing some straight uncompressed recordings?

    Several sites offer quite detailed measurements, but I'm not expert at understanding these, and differences all seem to fall within possible error margins. I'm simply thinking that a really good relative comparison would be to just soundproof a closet and run some tracks, preferably also from high resolution lossless files, at a range of volumes and microphone distances. Some real dynamic range classical, "noise war" pop, some operatic recitative is great for pinpointing hard to hear enunciation, maybe patch a phone in on speaker, to a conference call. Just enough so review readers could take, say, a half hour listen. Since so many have great headphones now, and many of those are studio monitor quality in flatness of response, I think this would work well.

    As a kid, I very nearly took my studies to pursue a interest in sound engineering, but that's a very long time ago, however I remember many psychoacoustics reviews linking attention and perception of quality to both sound and video quality, basically perceived visual acuity would improve with greater audio fidelity, and similar correlations.

    We spend a lot of time, now, with our phones. So much I have deliberately forgone use of anything but a very basic candy bar Nokia, just coming to six months now, exclusive use of a simple not even series 40 model, literally the flash ram is wearing out, it's so cheap. This is my last week or so!

    My point is, that even with phablet phones, viewing a video, is something you often share, and so hearing comparison at a meter between phones would persuade me over anything other than a real deficiency in the screen. Poor audio has been the thing that I find causes my companions or colleagues to have difficulty understanding, not video, provided the video is smooth.

    So having a idea of what these phones can sound like, for conferencing or music, at a meter or so, just as a comparison, forget graphs and numbers, would be really cool.

    Please forgive me, if I have missed out on the parts of your test regime, which might give me a idea, but I'd be persuaded by any well managed real life sample, over test reports. To a certain extent, it feels like the eighties again, or before then, really, when getting any decent sound was a result, and the word "audiophile" was invented to excuse the measurebating.

    I hope I'm not suggesting the all too obvious, instead just calling out a wish, but I was thinking the other day, about television reviews. About only one surprised me, to see something distinctly better, through YouTube's 1080 setting, and that as of a limited production Panasonic plasma, their last ever plasma. That seemed to shine through the obviously degrading signal chain. I am sure that great audio performance would shine through as well.

    Are speakers generally deprecated? I mean, do most users .. no, most review readers, pay less attention to speaker ability, because they presume they'll be using their (very good) own headphones? If I was writing reviews, and selling adverts or anything to do with it, I'd be on the case to find out some numbers and opinions.

    Thanks again & best from me,

    ~ joj
    Reply
  • fokka - Friday, September 05, 2014 - link

    i wanted to say the same thing, but you beat me to it.

    i hate having to read paragraphs of text, just to be able to tell what specs some device has. it's even worse when comparing different devices.

    here we always get a nice chart, often comparing the reviewed piece of tech with its predecessor or competing products. this way i have a good overview in a matter of seconds.

    thank you.
    Reply
  • JoJ - Monday, September 08, 2014 - link

    I agree with that, for sure!

    But I'm hijacking this early bit of the thread to as something dumb, that's kinda similar in terms of frustration with websites, or rather browsers: what happened to having text wrapped when you scale it on a phone or any other device for that matter? Opera Mini and Mobile used to do that, just fine. Okay, it did mess with layout a bit, but never so badly. Now I see no word wrap at all, and even in this Surface Pro 2, I don't have width enough when zoomed to appease older eyes, still keeping the page from overflowing... I simply do not want to horizontal scroll! Has anyone any ideas? I have tried lots of browsers, for sure, but no luck. Story of touch compatibility on a Surface is another thing altogether: I delayed the last Patch Tuesday because of the BSOD issue, and there's a few IE11 updates there. But, if a lot of things do not dramatically improve with IE11, I am going to write a very lengthy demand for a refund. That bad. On a metered connection and it won't recognize I darn well closed those thirty windows, two freaking shutdowns ago... and that's just one issue of many, and I really do wan to love this device...

    Anyone know what happened to text wrapping for mobile browsers?

    Why is - to my mind at least- such a vital usability feature not highlighted in reviews?

    I am windows centric, but could care less about which platform I use, when it comes to usability.
    Reply
  • hahmed330 - Friday, September 05, 2014 - link

    Yeah awesome and highly professional preview... Moto X looks really promising considering how much attention to detail they have put in each and every solution. Motorola shames Samsung when it comes to attention to detail. Reply
  • Peroxyde - Friday, September 05, 2014 - link

    Because other specialized "mobile" sites do quicker review. They shoot the phone with a bullet and check after if the phone is still working. Reply

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