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


View All Comments

  • saliti - Friday, September 5, 2014 - link

    Smart phones aren't exciting anymore. The only flagship that I like is the Note 4 because of vast improvements in S-Pen. For normal usage I would rather buy a cheap phone with Mtk 6592 in it.
  • Phrozenspite - Friday, September 5, 2014 - link

    Does the camera have optical image stabilization? Reply
  • JoshHo - Friday, September 5, 2014 - link

    No, it's EIS only. Reply
  • CrystalBay - Friday, September 5, 2014 - link

    Moto Nexus X (6) is rumured to have OIS Reply
  • RunAroundInCircles - Friday, September 5, 2014 - link

    After getting my current G2, OIS is a must for me personally. It improves low light shots to compensate a little for the (physically) small pixels in this sensor and makes the difference between a blurry mess and a decent shot in normal conditions.

    I also will not be purchasing another phone without either micro SD expansion or ideally larger faster storage. This NEEDS to become a priority in mobile. Hate to say it be the one to say it but 16GB or even 32GB just does not cut it anymore. How can apple be the only ones consistently offering a larger storage model (albeit at severely inflated price points, with wallet searing profit margins). And before any replies with 'the cloud has solved all my storage needs', come live in regional Australia, there are plenty of areas where there is no mobile service at all, let alone the data caps to use it.
  • modulusshift - Friday, September 5, 2014 - link

    The Moto X is legendary in storage performance, because of the use of F2FS as covered last year in the AnandTech review. I admit the size is still an issue, but Moto is squared as far as speed, I promise. I can't wait to see what other hidden tricks the engineers slipped in. Reply
  • gg555 - Friday, September 5, 2014 - link

    Yeah, I really would like to have OIS too and think of it as a must have feature. I'm a bit torn, because I also want good noise cancellation. Phones have been going backwards for a long time with noise cacnellation. The Nexus One used the Audience noise cancellation chip, which was great, but it never appeared in another Nexus phone. The iPhone 4 also had the Audience chip, but it was dropped in subsequent iPhones. Most people use Qualcomm's inferior Fluence noise cancellation these days (except Samsung, which has consistently used Audience in it's flagship phones). So Motorola's four microphone noise cancellations sounds very tempting. It will be hard to find a feature like this in another phone.

    By the way, your G2 has the Audience chip, but like other manufacturers it was dropped in the G3. It's horrible to see flagship phones go backwards.
  • alinsiddiqui - Friday, September 5, 2014 - link

    Motorola's website says the Moto X has only one speaker and the top is actually an earpiece, yet your article says that the Moto X has stereo speakers. You sure you're not wrong on that? Reply
  • JoshHo - Friday, September 5, 2014 - link

    Apologies, it seems that I spoke too soon on this issue. I have corrected the article. Reply
  • gg555 - Friday, September 5, 2014 - link

    Wow, that's a disappointment. It's one of the features that tempts me about this phone. Seems like the way Motorola designed the earpiece and speaker to look identical is almost a deliberate attempt to mislead people. Reply

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