🚀 go-pugleaf

Jeff Liebermann <jeffl@cruzio.com> wrote in 
news:rnss361grsdicbd06rbajlgniho8d4877o@4ax.com:

> There's another related possibility.  Most of the finger tests have
> been with the finger bridging the gap.  That means they're touching
> BOTH the cellular and wi-fi/BT antennas.  It's obviously the hot end
> of the cellular antenna, but I can't tell if it's the hot end or
> ground end of the wi-fi/BT antenna.  If the hot end, another
> possibility it that coupling to the 2nd antenna causes this antenna to
> radiate into the case, thus causing the cellular front end to
> oscillate.  If the oscillations are bad enough, the signal level will
> be high enough to induce blocking (overload) in the cellular front
> end.  This can be easily detected with a spectrum analyzer probe in
> the vicinity.  If touching/bridging the antennas causes a new signal
> to appear on the SA, that's the problem.
> 
> It would be very interesting to know if touching ONLY the cellular
> part of the antenna (the part that goes up the side of the phone), and
> not the wi-fi/BT antenna (bottom of phone), causes the same drop in
> signal.  It would also be interesting to test the wi-fi signal
> strength to see if it's effected by touching its antenna.
> 

Jeff, they wouldn't let me do much at the ATTWS store and were watching 
me like a hawk so I couldn't get the phone into test mode, if test mode 
was still available.  But I did have a fair bit of time to play with the 
antenna gap while he was giving me the sales pitch I was ignoring......

http://www.antenna-theory.com/antennas/aperture/ifa.php

I believe, though it's very hard to see on the ifixit teardown photos, 
IP4 is using IFA slot antennas like the Palm uses depicted in this 
website.  There only needs to be one IFA for each band and they are very 
broadbanded, though buried in so much METAL, the idiots have effectively 
transmitted INSIDE a near shield with only a coupling slot out of the 
cavity across the bottom for these antennas to radiate through.  The 
coupling slot would be very high impedance and the meat of your hand 
would be a near short to this high impedance, voltage-fed escape route 
out of the glitzy metal box Jobs loves to sell.  We would not be hearing 
any of this if he'd simply made the back out of plastic so the various 
IFA antennas radiation patterns could send RF through it.  It was a 
major blunder that's going to cost him bigtime.

The website explains the theory behind the IFA slot antennas.  This 
technology is nothing new, predating cellular phones by a few decades as 
it was used in microwave devices in this frequency range before.  The 
difference on the Palm, which doesn't have this problem, is the Palm has 
an RF transparent back that leaks RF like a piece of glass so RF gets 
out no matter how you hold it.  Not so on IP4 with its metal case and 
little slot.

The website has a great explanation.

In answer to your question, anything you do to touch near that slot 
bleeds off the signal into your resistive skin very badly.  Waveguides 
don't like you touching their slots.  The gap impedance is in at least 
10-100K ohm range.