Friday
Jul022010

First Impressions: iPhone 4

I did not expect to be posting this before my personal iPhone 4 arrived, but my friend Keith showed up with his shiny-new iPhone 4.  We did a quick test in my office; this is not an exhaustive test, but it's a start.

First, we placed a call to Paul, another iPhone 4 user.  We were going to invoke FaceTime, but I realized that our firewall was too tight - FaceTime requires some ports opened.  We'll play with that another time.

The Two-Finger Suspension GripWhile on a live call, we held the phone from the top, and observed five bars.  Then, I asked Keith to give the phone a two-handed Grip of Death.  After a delay of perhaps fifteen seconds, the signal strength fell to one bar.  Regardless of how we applied the Grip of Death, we could not cause the call to drop.  I realize this says more about my local signal strength than it does about the phone.

Then, we used electrical tape (white) and wrapped the "band" on the lower half of the phone.  Then we repeated the test, again with a live call.  The results were identical.  There was no discernable difference when we used tape.

Finally, we repeated the test with my Primordial iPhone (a first generation model), and got the same results, except instead of five bars, we started with four bars.  Do I think that difference was significant - no, I do not.  We still have no idea what the bars mean, especially in the different models.

We did not spend a lot of time, mostly because we were heading for a sushi lunch, but I did draw a couple of preliminary conclusions:

1) The iPhone 4 is not nearly as hypersensitive to "hand" effects as I was being led to believe from the media buzz.

2) The iPhone 4 seems to be as sensitive to hand effects as the Primordial iPhone.

3) Electrical tape over the "band" did nothing.

The Two-Handed Grip of DeathI had predicted in a previous blog posting that the application of electrical tape would not do much, and nothing in this first test implies otherwise.  I was frankly surprised that the Grip of Death did not affect the iPhone 4 any more than the primordial iPhone.  I was quoted in the press as saying that we're "making a mountain out of a molehill".  It may be truer than I thought.

Today Apple released a letter indicating that they were "stunned" to learn that their signal-bar algorithm is "totally wrong", and has been so since the first iPhone models.  According to Apple, it was indicating 2 bars more than it should.  Further, AT&T has "recently" suggested a standard, and Apple will issue a software patch so that the signal-bar display will conform to this standard.

I've said it before, but now let me say it slightly differently: the only worthy metric for the quality of the cellphone is frequency of dropped calls when compared with other phones used in the same manner, over time.  You cannot tell the difference between a "one-bar" conversation with your mother, and a "five-bar" conversation. (This is not be confused with having a conversation with your mother FROM a bar, which I don't recommend.) The only way to observe dropped calls is to use the phone for a statistically significant amount of time.

So, if you are a Bar Watcher, Apple's letter is going to change your observations.  If you are a Dropped Call Counter, it will mean nothing.  Bar Watching has no value in my opinion; I think it is a waste of your valuable time.  If you have a routine that has you driving/walking/riding the same route every weekday, you probably know where your "holes" are.  This is how a Dropped Call Counter is going to make observations.  Apple's letter does nothing but divert attention from your valuable observations.

My opinion is that it's good that Apple is conforming to a standard.  Beyond that.... it's spin.

More details to follow.  I will be receiving my iPhone next week. 

Wednesday
Jun302010

iPhone 4 Testing Soon, But First...

Arrrrgh!  What to do while you wait?  Enjoy Independence Day with your family.  I promise to be back with first hand impressions of the iPhone 4 and its antennas soon.

Meanwhile...

 

See more of Scott Johnson's work at MyExtraLife.com.

 

 

Saturday
Jun262010

Hey, Hold the Phone!! (Like this...)

Photo by Steve Golson

I hit a nerve on Friday.  

The iPhone 4 antenna controversy was way bigger than I realized. The traffic to this site was incredible, and the extent of the blogs and news sites that picked up my comments was humbling.  I also did four telephone interviews, including the Wall Street Journal - they asked for photos, so we had some fun.  And yes, I did call it the "Vulcan iPhone Pinch".  And no, Leonard Nimoy has not called.

I received many emails, too.  The overwhelming tone of the email was very friendly; I wish I could respond to all of them immediately, but I am afraid that will have to wait.  I will try to touch on the topics raised in some of the emails in this blog entry.

First off, I still don't have my iPhone 4 yet.  Sigh.  I am waiting patiently, so keep in mind that all my comments are based upon my experience with designing embedded antennas, and not with the specific antennas in question.  I promise to post my first-hand experiences here once mine arrives.  Also, I don't have any Apple-specific information that you don't have access to.  I am not a consultant to Apple, and have never been; I don't even play one on TV.  I don't have an axe to grind.  Nor an iPhone 4 to play with.  But, I digress...

I have seen mention of the electrical tape fix, the scotch tape fix, the bumper case fix, even the short-the-other slot fix on various web sites.  The important thing to realize is that we are dealing with radio frequency (RF) currents in the antenna, not direct current (DC) as you will find in a flashlight, for example.  If you place a thin insulator (tape) across the "gap" and over the "band" on the iPhone 4, I would not expect that to make a very big difference.  With such a thin insulator you are effectively preventing a short at DC (zero Hertz), but at the RF frequencies involved (around 1GHz, or one billion Hertz) you are just making a large capacitor.  A capacitor is fundamentally two conducting plates separated by an insulator.  When the capacitance is high enough (plates big, insulator thin) at the frequencies in question, it looks just like a short circuit.  So, I would not expect tape to create any improvement when the Grip Of Death is used (see photo).

When I was on the phone with the WSJ, I explained the two distinct effects that holding the phone over the antennas will impart: detuning and attenuation.  

Detuning can be understood by imagining a wine glass that is empty.  If we tap the glass with a fork, the glass will ring, or resonate, at some frequency.  If we put some wine in it (or apple cider, since I don't imbibe) the resonant frequency will change and in this case increase.  This is the same for antennas.  Antennas are generally resonant at their frequencies of operation, and when we put our hand over them we "load" them with the dielectric of our bag of salty water.  This lowers the resonant frequency of the antenna and may make it harder to squirt energy into it at the frequency we want.  If the antenna is particularly narrow-band, it may "kill" it completely.  Generally, physically small (compared to a wavelength) antennas are narrow-band and large antennas may be wide-band.  This is why detuning is the first detrimental effect of putting your hand on an antenna.  Any antenna.

The second effect is attenuation, or loss.  Your hand is a dielectric, meaning it concentrates electric fields more than air.  This factor is called the dielectric constant, and for your hand is pretty high, like 12 or 20 or so.  It depends on your diet and BMI, so it's kind of personal and I don't want to make anyone uncomfortable by dwelling on it; the important thing is to be healthy.  Oh... right.... so this is what detunes the antenna.  But, your hand is also conductive, but not perfectly so.  So you WILL get a shock if you stick your thumb in a light socket, and I don't recommend it.  This not-so-perfect conductor is what we call "lossy".  RF energy impinging upon your hand (or head) is partially going to be turned into heat.  This is the SAR we were talking about, and you may have heard of.  This leads to an attenuation (reduction) in the signal being radiated into space by the antenna.  This is the other bad thing that happens to hand-wrapped antennas.  Once turned to heat, the RF energy is gone.  Just ask your dinner in the microwave.

So, detuning causes problems with squeezing energy from the circuitry into the antenna (or vice versa), and attenuation causes problems with losing energy to heat.

The so-called bumper case is a much thicker insulator (or dielectric) than a piece of tape. It pushes the lossy dielectric (your hand) further away, significantly reducing the capacitance.  I would expect this to reduce the detuning effect, but not the attenuating effect.  Will it help?  You betcha'.  However, it is a tradeoff: pushing a very high dielectric constant but lossy material away, and substituting it with a lower dielectric constant material.  If I were a betting man, I would guess that the dielectric constant of the materials used is about 3.3.  So, it still will load the antenna, but not as much; and it is entirely possible that this was taken into consideration in the design of the antenna.  Since I have had a case on my Primordial iPhone since it was new, I expect to do the same with the iPhone 4.  When it gets here.  Any time now.

Now I want to rant a bit about the "experimental method" people have been using.  The iPhone 4 was out for roughly 24 hours before people were publishing the results of "tests" proving that it had inferior performance.  At my company, when I get to hook my fancy laboratory gear up to my client's equipment in very controlled circumstances I can't do it that fast.  Folks, there are a couple of reasons that you need to give this product some time before jumping to conclusions.  

First, we have no earthly idea what those little bars in the upper left corner of our screen really represent, yet we are staring at them like they're going to help us find out what those damn numbers on LOST meant.  Steve Gibson of Gibson Research (grc.com) did a great piece on the meaning of the signal bars; I am a huge fan of his, and his measured approach to technical challenges are worthy of our respect.  We don't know what the bars mean, beyond more is better and less is ... less better.  We also don't have a handle on the time constant of the bars, which is to say we don't know when the bars change with respect to when the signal changes.  And worse, we don't know if it's consistent.  After all, it's controlled by software.

Secondly, the cellular system is composed of many cell sites.  While you are making observations, you have no idea whether your iPhone is staying on one cell site, or switching between several.  This will completely obfuscate any measurements, even if you decided that the bars are useful.  In the good old days, when cell phones worked on steam, there was usually a service screen you can hack your way to which would show which site you're on, and how strong it was in real engineering terms (dBm).  I have never seen that capability on the iPhone (but, I didn't look too hard).  Such a capability would be hugely helpful in our experiments.

So, how do we evaluate the performance with these limitations?  The answer is: over more time, in more situations.  You need to observe more bars in more places.  (I know, cheap shot.)  Give it a couple of weeks.  Use it like you used your last phone.  If it doesn't make you happy, return it to Apple.  But, give it a chance, and 24 hours ain't it.

Several reporters wrote that I "blame the FCC for the iPhone antenna problems."  Well, I did say "it's the FCC's fault", but I was a bit glib.  It's the whole process that drives the design (I did say that, too), and part of that process is the tests the phones must pass.  And the FCC could care less whether your phone drops your calls in the middle of a conversation or not; they care about protecting the "spectrum" and safety.  AT&T does care about efficiency, but they assume your hand is made of styrofoam.  Apple cares about striking a balance between product coolness (you'll buy it) and product efficacy (you'll keep it).  All of these pressures lead a product to the end point.  And then the unpredictable takes over anyway, so enjoy the ride.

So, why didn't Apple do it differently?  That's a question I thought about through several showers.  I have finally boiled it down to one thing: any performance improvement would have made the iPhone 4 bigger.  Period.  Apple is putting ten pounds of stuff in a five-pound bag.  Put air space around the antenna to make it less sensitive to the presence of the human hand?  Fuggetaboutit.  Air doesn't sell phones.  Gyroscopes, accelerometers, high resolution screens, multiple cellular carrier capability (did I say that?), and big batteries.... that's what the people want.  

You just gotta hold it like this.

Thursday
Jun242010

Apple iPhone 4 Antennas...

I received a phone call today from PC Magazine.  They were running a story on the new Apple iPhone 4, specifically the reports (PC Mag, Gizmodo, Engadget) that people are experiencing decreased reception on their cell phone when they hold the phone by the metal frame.  That frame has been touted by Apple, in the keynote address by Jobs, as being part of the antenna system.  Here is a brief summary of what I told the reporter who called me, and a little extra. (The reporter was Mark Hachman, News Editor, PCMag.com/ExtremeTech.com.)

I saw the photo of the frame of the iPhone in the slideshow at the end of Steve Job's keynote address at the Developers Conference.  There are three gaps in the stainless steel band which are allegedly part of the antenna system.  I have not had a lot of time to analyze their structure, nor do I have one in my hands yet.  So, either it is public relations hokum, or those slots are really part of the antenna structure.  They do appear to be active, based on observations.

In the first generation iPhone (which I am currently using), the antennas were on the back of the phone, near the bottom.  There was a piece of plastic on the bottom covering the antennas, so you knew where they were.  I developed a way to hold the phone which avoided covering this area with my hand, similar to the Gizmodo article linked above.  It is worth stepping back a moment and asking the question, "Why are the antennas placed where my hand is MOST likely to cover it?"  It's a fair question.

The FCC puts strict limits on the amount of energy from a handheld device that may be absorbed by the body.  We call this Specific Absorbtion Rate, or SAR.  In the olden days, when I walked ten miles to school in three feet of snow, uphill in both directions, cell phones had pull-up antennas.  This allowed the designer to use a half-wave antenna variant, and put the point of maximum radiation somewhat away from the user's cranium.  Of course, most people did not think it was necessary and kept the antenna stowed.  Motorola's flip phone acutally had a second helical antenna that was switched into place when this was the case.  But, more importantly, SAR rules were not yet in effect.

Flip phones became yesterday's style, and phones were becoming more monolithic.  Some phones, like the early Treo, kept the antenna in the traditional location at the top of the phone, near one edge, but reduced it to a short stub.  Whips became stubs, stubs became bumps, and finally antennas were embedded into the rectangular volume of the phone.  The trouble was SAR; if you left the antenna at the top, the user was now pressing it into their head, insuring lots of tissue heating.  Enter the bottom-located cellphone antenna.

Just about every cell phone in current production has the antenna located at the bottom.  This insures that the radiating portion of the antenna is furthest from the head.  Apple was not the first to locate the antenna on the bottom, and certainly won't be the last.  The problem is that humans have their hands below their ears, so the most natural position for the hand is covering the antenna.  This can't be a good design decision, can it?  How can we be stuck with this conundrum?  It's the FCC's fault.

You see, when the FCC tests are run, the head is required to be in the vicinity of the phone.  But, the hand is not!!  And the FCC's tests are not the only tests that must be passed by a candidate product.  AT&T has their own requirements for devices put on their network, and antenna efficiency is one of them.  I know because I have designed quad-band GSM antennas for the AT&T network.  The AT&T test similarly does not require the hand to be on the phone.  

So, naturally, the design evolved to meet requirements - and efficient transmission and reception while being held by a human hand are simply not design requirements!

OK, back to the iPhone 4.  The antenna structure for the cell phone is still down at the bottom (I won't address the WiFi nor GPS antennas in this blog entry).  The iPhone 4 has two symmetrical slots in the stainless frame.  If you short these slots, or cover them with your hand, the antenna performance will suffer (see this video I found on YouTube).  There is no way around this, it's a design compromise that is forced by the requirements of the FCC, AT&T, Apple's marketing department and Apple's industrial designers, to name a few.

One of the questions the intrepid reporter from PC Magazine asked me was, "Will putting the phone in a pocket and using a Bluetooth device help?"  Good question.  The answer is yes, to a point.  The first generation iPhone clearly had a conductive surface below the antenna (I hesitate to call it a ground plane, because it is too small).  So, putting it in your pocket with the screen toward your body and the antennas facing out while using your Bluetooth earpiece will work better than holding the phone with your hand.  In fact, in my car my iPhone sits forward on the dashboard, under the windshield, screen down while I use my Jawbone.  Works great.  (However, if you put your iPhone in your left back pocket, and your earpiece in your right ear, you may have issues.  This is a failing of the Bluetooth system in dealing with severe body losses at 2.4GHz, not the cellphone's problem.)

The iPhone 4, however, moved the antenna action from the back of the phone to the sides.  This probably improves the isotropy of the radiation pattern, but only when the phone is suspended magically in air.  Not too helpful.  Putting this iPhone 4 in your pocket will likely couple more energy into your body (you bag of salt water, you) than did the first generation model.  Yep, I predict it will be worse.

So, what's an iPhone lover to do?  Well, I voted with my dollars.  I ordered my iPhone 4 to replace my Original.  I already know how to do the Vulcan Antenna Grip on the iPhone, and I am wearing out my current model.

And sometimes an antenna that's not great, but good enough, is good enough.

 

Sunday
May302010

30 dB in 30 Minutes...

A couple of years ago: the phone rang, and it was another potential client.  A referral from a referral... in any event, they thought they had an antenna problem.  They were right.

It seems they were building an interesting on-body medical sensor which included a data transceiver for a clinical application. (If this sounds familiar, it should.  These days, I seem to do many projects with "on-body" and "medical" in their descriptions.)  This transceiver was at 2.4 GHz, and the size of the device was bigger than a wristwatch, but smaller than a deck of cards; it was powered by a coin cell.  It was located on the body of a patient in a hospital ward, and it needed to communicate with a central monitoring station about 25-50 feet away. Presently, it was doing a lousy job of it.  Sometimes, they had to lay the receiver on the patient's chest to get the data.  This was not only not good, it was not wireless. 

I needed to know where the client wanted me to take them. "What is your goal?"

"We need these 25 systems to work for the clinical trials.  The hardware is all built, and time is short.  It doesn't have to be pretty, but it has to work."

I scheduled a one-day session for them at my lab.  At worst, I thought, we'd get to the bottom of the problem and at least know what was going on.  At best, we'd solve the problem and know how to modify the built units.  I made sure the benches were (sufficiently) cleared off, the spectrum- and network-analyzers were warmed up, and the 'fridge was stocked.

They had built up 25 of these devices for a clinical trial; a sort of beta-test, but with lots of interested parties paying close attention.  The issue of way-too-short-range of the data link was not the death knell of their product, because they had really cool sensor technology which was the primary focus.  But, it wasn't going to impress anyone either.  They wanted the problem solved.  Now.

The Senior Engineer on the project showed up at my lab at the appointed time of 10:00am, and we got down to business; we'll call him Joe - not his real name.  He brought several of the sensors, complete with extra batteries and spare units I could play with.  He also brought their prototype monitoring unit, which had a simple off-the-shelf sleeve-dipole antenna on it.  We fired up one of the sensors, and it began transmitting packets of data about once every ten seconds.  

Sure enough, the receiver had to be within about two or three feet in order to hear the signal.  Not good.  I asked Joe lots of questions about how the unit gets deployed in the field, where the receiver would be set up, what the design of the receiver was, and so on.  I set up our spectrum analyzer and a calibrated dipole to observe the signal.  Man, that was one weak signal.  With Joe's permission, I cracked open the case of the unit.

Joe explained that they were using a Chipcon transceiver chip (now TI), and they followed the data sheet's schematic exactly.  Further, they made a "loop" antenna following some design equations one of their engineers found in the literature.  Hmmm.  I looked at the loop of wire, and something was bugging me.

"What was the calculated size of the loop?," I patiently asked.

"I believe it was one-half wavelength," Joe patiently explained.

"Did you say ONE-HALF wavelength?"

"Yessir."

If you see where this is going, congratulations.  Joe didn't, and his folks back at the office sure didn't, and that's why he was in my office.  I carefully measured the dimensions of the wire antenna they had made and noted it in my lab notebook. It was sort of a fat folded-dipole shape.  I took pictures to document everything (a habit of mine that often pays off in 1000-word increments).  Then, I opened my toolbox and removed the most powerful weapon I had.

I readied my high-quality wire cutters.

"Joe, watch the spectrum analyzer carefully."

With both his eyes on the screen of the analyzer, and mine split between that screen and the device, I cut the wire right at its midpoint.  The formally puny peak on the screen jumped up.  A bunch.

"Um, that just went up 30 dB."

"Yessir."  It was my turn to savor my favorite moment as a consultant.  If Joe smiled any broader, his face was gonna break.

"OK... what's going on??!", Joe asked.  It was 10:30am.

I explained that somebody's slide rule slipped.  If you make a loop of wire, and I don't care what shape, with one half-wavelength of wire, it's going to look like a shorted quarterwave transmission line, and very close to an open-circuit.  If it was going to be a loop, it should have been smaller and resonated with a capacitor, or longer and about one-wavelength long.  It was about as perfectly wrong as it could have been.  Snipping the wire at the center point essentially made it a dipole, with each leg folded back on itself.  Probably not very efficient, and probably not well impedance-matched, but... 30 dB better than what they had.

I showed him how to open each unit, snip the wire, tape the ends in place and get on with their clinical trial.  He left a happy engineer.  The clinical trial was a success, their product worked, and life was good.

After the clinical trials, I was invited to redesign their PC board, and put a custom antenna on it.  We ended up designing a cool embedded antenna which used the PC board copper and ZERO matching components.  If memory serves, we eliminated somewhere between four and six components.  The new antenna was designed and optimized using our CST Microwave Studio tools.  We optimized the antenna in situ, taking into account the battery, PC board, housing and the human body.  Performance was excellent; it worked just as envisioned in the clinical environment.

With much gratitude, I can report that we are still working with this happy customer.

Sometimes, you win the game by making base hits and hustling in the outfield.  You fight for every inch.  But, sometimes, just occasionally, with the bases loaded and the wind blowing in the right direction... you get 30 dB in 30 minutes.

I wish I could do that all the time.