On Sun, 12 Oct 2014 14:14:53 -0700, Jim Thompson
wrote:

On Sun, 12 Oct 2014 14:03:08 -0700, RobertMacy
wrote:

On Sun, 12 Oct 2014 13:25:32 -0700, Jim Thompson
wrote:

On Sun, 12 Oct 2014 13:17:04 -0700, RobertMacy
wrote:

On Sun, 12 Oct 2014 12:45:29 -0700, Jim Thompson
wrote:

I need a SWAG on this, just to see if it's feasible...

Two inductors (solenoids) with Ferrite cores, each ~5mm in diameter
and separated by ~5mm spacing.

What coupling coefficient might I expect?

(Essentially no load on the "receiving" inductor except natural
losses... and I could tune or not.)

...Jim Thompson

5mm rods, how long? what orientation? end to end? side by side?

audio ferrites? low perm ferrites?

I don't know. What would be best? ~100kHz sinusoidal drive

...Jim Thompson

obviously, best orientation depends on length.

from memory rods usually are 4:1 up to 10:1 aspect ratio rarely longer,
they break pretty easily. surprisingly the aspect ratio determines more
the 'effective' permeability much more than the basic permeability, like
with a 4:1 anything with more than 100 rel perm makes NO difference.

do you have any way to 'close' the magnetic path just a bit? Tuning
makes
a BIG difference! on getting a huge voltage out of it.

I can make some 'guesses' or spend some time to look at it in a bit more
detail over night and get back to you with justifications for why do
this
versus do that.

Cross talk you can get some good estimates. If this is for a
'communication' at all; we should discuss that a bit too.

This is an RFQ for a slow speed (~100bps) data link "magnetically",
with ~5mm gap.

I'm just wondering feasibility before sticking my neck out.

...Jim Thompson

Full-duplex? piece of cake! I've done that using air core PCB coils [no
winding necessary] and operate over a distance of 8 inches using less than
3.3Vdc, 5mA per TxRx pair. Also, no tuning required, no 'touchy' high
tolerance analog parts. PLUS, not even catch the attention of FCC, operate
in a true don't care band.

100bps! I'ved designed systems that communicate MILES, through salt water
to do that!

no 5mm, 100bps full-duplex, piece of cake.

Big hint: communication between two entities should NEVER be treated like
a radio transmitter/radio receiver pair. leave THAT for the broadcast
industry where ONE talks to many. Rather THINK SYSTEM! where BOTH must
communicate hand in hand, not simply throwing information out there hoping
the other stumbles over it. Thinking system will get reliable cheap
communication that even instantly flags you as the link starts to weaken!

Sorry, have to get offline for a bit, painting here.