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

  • Klug4Pres - Friday, September 5, 2014 - link

    Tiny, non-replaceable battery, no sd card, poor camera, year old SoC. Specs are not the only thing, but you still have to be competitive. Does Motorola actually want to sell phones? It seems as though they are content just to demonstrate a few peripheral technologies.

    Oh well, they are a patriotic buy for US citizens.
  • smorebuds - Friday, September 5, 2014 - link

    Hyperbole much? 801's been shipping in devices for like 6 months. Reply
  • coburn_c - Friday, September 5, 2014 - link

    5.2 inches is a great size for a screen, 2300mAh is not a great size for a battery. 2300mAh in a 5.2 is a disturbing size for a battery. Reply
  • Mugur - Friday, September 5, 2014 - link

    Nice preview.

    All in all the phone seems ok, with a few caveats: small battery and the front looks too similar with Samsung's S3, S4, S5... And this is not a compliment. :-)
  • Zoomer - Saturday, September 6, 2014 - link

    Moto Maker will likely let you customize it to black. Wish the speaker grills are black or laser cut holes, however. Reply
  • passive - Friday, September 5, 2014 - link

    The original Moto X used Nano SIM as well (having had to cut my old SIM down manually, I know this quite well). The comparison table is wrong. Reply
  • irev210 - Friday, September 5, 2014 - link

    If you aren't familiar with Horween Leather it's basically the best leather money can buy. A handful of japanese tanneries are the only competition to Horween.

    They started business in Chicago in 1905 and have been in the same place ever since. They use VERY old school vegetable tanning methods and very high quality hide. I recommend looking at some tour photos or blogs about horween and where they make their leather.

    As for durable - I walk on horween leather (100% leather, no rubber) just about every day (old school, I know). So when you said "although a few years of intensive use may make the latter a terrible idea" I was extremely surprised. The horween leather would likely hold up better than standard plastic or many other materials. It took me a long time to figure out that most leather used sucks and high quality leather is extremely durable.

    Horween leather is extremely expensive. It's extremely surprising that Moto is using Horween - it's very unusual.

    Hope this is helpful information.
  • Zoomer - Saturday, September 6, 2014 - link

    Josh might be commenting about the smell, since leather is porous. Leather cleaner/conditioner and Cedar phone mats anyone? Reply
  • apertotes - Friday, September 5, 2014 - link

    Motorola presented a great smartphone, but it is not the Moto X. Reply
  • melgross - Friday, September 5, 2014 - link

    Held back by bad timing poor distribution and, most importantly, bad execution. The phone really wasn't all that good.

    I'll be really interested to see whether this one is as good as Moto says it is.

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