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

  • louisejhocker - Friday, September 5, 2014 - link

    just as Larry answered I didnt even know that people able to get paid $6104 in a few weeks on the internet .
    go to this site>>>>> paygazette.ℭOM
  • randomlinh - Friday, September 5, 2014 - link

    "although dual front facing speakers are now used instead of a single rear facing speaker"

    Hrm... other sites are saying it's not dual front speakers, only the bottom is. Top is still just an earpiece?
  • JoshHo - Friday, September 5, 2014 - link

    I distinctly recall being told that the Moto X had stereo speakers but it seems they were mistaken. I'm correcting this now. Reply
  • gg555 - Friday, September 5, 2014 - link

    Why would they put stereo speakers in the new Moto G and not the X? Are you sure about this? Reply
  • Stochastic - Friday, September 5, 2014 - link

    Hmm, $500 off-contract is a bit steeper than I would have liked, especially since you probably have to spring an extra $100 to get the 32 GB version. Honestly, I wish Motorola offered a no-frills version with the same specs but without the voice and sensor features at a reduced price point. Nevertheless, the attention to detail is impressive, and overall this seems like a well-rounded phone.

    Also, nice write-up Joshua! One thing I think you really excel at is explaining technical things to a layman such as myself. Anandtech has always been technical, but some of the writers just assume that their audience has the background knowledge to understand everything without explanation. You tend not to do that.
  • Stochastic - Friday, September 5, 2014 - link

    To be fair, I think most of the staff do a good job of this, too. Reply
  • jeffkibuule - Friday, September 5, 2014 - link

    32GB version is $50 more. Reply
  • emailrob - Friday, September 5, 2014 - link

    To an extent, that's the new moto g IS their no frills version without the additional sensors. I have the current moto X, but am disappointed and don't think I'll be upgrading. Maybe even a downgrade to the moto G (I did have the original one).

    I'm overall disappointed with the price point and the battery life.
  • rocketbuddha - Friday, September 5, 2014 - link

    In 2013 MotoX with a 720p and dual core Krait 300 based SOC (plus its custom processor) had a launch price of $579. At that time other flagships at price point were 5" + FHD screens with better SOC S600/S800 with bigger batteries, expansion etc. Atleast this time Moto geniuses came to planet earth :D

    I would not be surprised it ended up like its predecessor with 299$/$349 (16/32) special flash sales that cropped up multiple times this year. Wait for 3 mths and you will see that happen :D

    Touche abut Josh's writing. This is the kind of extra detail that Anandtech alone provides among most sites and keeps it distinctly original amongst the techno babble.
  • trevorftard - Friday, September 5, 2014 - link

    The current moto x uses a nanoSIM FYI. Reply

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