How to create an inductor 2.mH with a toroid core ferrite?

You should have looked at a nickel-zinc ferrite core. Nothing else is resistive enough to work with a 5MHz pulse stream - the pulses have harmonic content up from 5MHz to an upper limit set by the pulse width.

They don't offer particulary high permeabilities, but you don't tend to need much at those sorts of frequencies.

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vered

And silvered copper wire tends to be electroplated, and electroplated silve r is less conductive than bulk silver. You could probably flash heat the el ectroplated layer with a fast power laser, and melt the silver layer withou t letting it alloy with the copper. Using silver-plated wire for RF coils i s a ham tradition, but serious engineers haven't bother for decades now.

ers

not move about.

But ham-handed operators are unavoidable.

Magnetostriction will create vibration. 5MHz means the amplitude won't be much, but the fracture mechanics depend on energy levels, not just amplitude.

What's the objection to dropping a 90 degree angle through the board at each end of the coil?

Clifford Heath.

Some applications let you select two pulses next to each other, etc. A duty-cycle kind of thing.

This inductor is heat sunk. It needs to be.

Pot cores are usually electrically conductive. I have 1200 volts here.

Potting is a mess.

I can wind this coil in one minute. It works fine.

What is that, a 1.2kV flyback inductor?

Ah, I can see that would be a problem.

Well, just make sure the solder fillet radius is big enough to relieve the stress riser, and test it.

Clifford Heath.

Top secret, but sort of a matching network that I didn't expect to get hot. Designed by Spice fiddling, so I barely understand how it works.

On a sunny day (Mon, 01 Jul 2019 16:20:57 -0700) it happened John Larkin wrote in :

Ceramic coil formers do make heatsinks, and if mounted vertical can be made mechanical rigid. You could tap into the heatsink for mounting. that would draw away heat from the ceramic. The coil top connection lead length would add some inductance, matter of testings if it works. Or mount the ceramic former horizontal with brackets screwed into the heatsink below, some epoxy perhaps.

No thermal foam under the coil needed...

I have used those ceramic coil formers with tubes, class B output linear with 500 V anode voltage (~1 kVpp) 250 W CW, about 7 MHz, mounted on a steel plate,

Nickel Zinc ferrites are less conductive than the regular managanese zinc f errites, which is why they remain useful up to hgiher frequencies.

So is designing magnetic components so that they will do the job you need t o be done.

Tinkering creates a different kind of mess.

But gets hot, and is vulnerable to mechanical deformation.

Fewer turns around a nickel zinc ferrite core might less you use heavier wi re and the assembly - including the ferrite - might dissipate less heat and might be more compact. You'd have to find your nickel zinc ferrite cores, which might take some work - they weren't high volume items when I last loo ked at them, which was a while ago.

Series-resonance peaking. Sneaky.

But not exactly top secret. John Larkin does re-invent the wheel a little too frequently for somebody who claims to do electronic design.

One think that's fun is to sort of randomly stick inductors into circuits to see if they speed things up, to make exponential things more critically damped. I'd like to get good with t-coils, but they are harder to manufacture than just buying inductors.

The coil could be wound tight on an alumina or AlN rod, which would spread out the heat some. A machined spiral groove would be ideal, but hard to fabricate.

The gap-pad stuff isn't bad in production. It seriously drops the coil temperature.

Epoxy is always messy, so we try to avoid that.

Which p/n of gap pad are you using?

TW-T600-2MM from 3G Shielding. It's rated 6 W/mK, which it actually does if compressed pretty good.

with 500 V anode voltage (~1 kVpp) 250 W CW, about 7 MHz, mounted on a steel plate,

Micro-cracked alumina is machinable. The trade name is MACOR.

It's thermal conductivity isn't great, but better than air.

"Messy" just means that you haven't worked out a way to do it tidily yet.

I have their designer's kit, but they seem to have roughly zero distribution. Where do you buy it?

Cheers

Phil Hobbs