On Wed, 14 Jul 2010 23:02:21 -0700, Jeff Liebermann
wrote:

However, the -30dB
drop of the iPhone 4 requires some extra circuit design screwups.
Unfortunately, detecting the regeneration is going to require internal
probes, test fixturing, and plenty of expensive test equipment.

Hi Jeff,

Regenerative designs inhabit the naked edge of
amplification/oscillation. You've already said as much. It has to
be, thus, a design feature and not a hack. Otherwise every third one
is going to break into oscillation and the FCC (or test lab) would
have certainly picked up on that. Further, if it is designed in, you
can observe that in the design. Special testing methods are too
elaborate to explain this. Regen is not a design feature left to the
vagaries of production variation in parasitic coupling.

If I'm wrong and Apple does use parasitics to encourage regenerative
feedback, then they may introduce a lanyard for hanging the phone
around the neck and call it the lavaliere option. No doubt they will
sell plenty of mirrors to see it, and someone will come out with an
image reversal app. Can a stylus be far behind? Whoops! It will
have to be chopstick for squeezing and expanding images.

73's
Richard Clark, KB7QHC