John Hague wrote:
On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction?

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or
a couple of holes in the board and a cable tie. The only thing to
avoid is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down
on a solid copper plane? I thought the magnetic field was contained
within the toroid and thus minimised external effects. I have completed
a couple of projects recently with some of the inductors like that and
didn't notice any real problem. Mind you, I guess they might have
performed better if not mounted that way )

Two potential problems. One is that the field isn't completely
contained. Leakage is greater with more sparsely wound toroids and ones
with lower permeability cores. The second is the "one turn effect" -
There's a net field equivalent to that of a single turn running
circumferentially around the core. A solid plane parallel to this would
act as a shorted turn. Both effects would act to lower the Q, and might
be the cause of some drift or microphonics if the inductor was in an
oscillator tank.

But to be honest, I've never run any experiments to see just how much of
a problem it might cause -- it's quite possible you could get away with
it in some or even most applications. I'll put it on my list of things
to do when time permits -- unless somebody else is willing to take on
the job.

Roy Lewallen, W7EL