1-MHz LC oscillator - position of the inductor wrt ground plane

Thread Starter

atferrari

Joined Jan 6, 2004
4,093
I am trying to build an LC oscillator for 1 MHz.

The 44 MHz inductor is winded around a ferrite toroid.

Is it any previsible problem mounting it lying on its side directly on the ground plane?

L1 44uHy.jpg
 

Thread Starter

atferrari

Joined Jan 6, 2004
4,093
Hello,

On this page : http://www.worldofindie.co.uk/?p=900
You will find this picture of the manhatten style prototyping using an inductor like yours:

View attachment 217010

Bertus
Hola Bertus
It seems to be somewhat separated. The wire in mine is rather thin so I should create kind of mounting to keep it in position.

I ask again the same initial question: what if the inductor lies on the ground plane?
 

ronsimpson

Joined Oct 7, 2019
932
A toroid coil has very little flux (magnetic field) outside the core. There will not be a problem. If this was production, then I would use some kind of insulation like in the picture. Magnet wire does not have good insulation and with years of rubbing on the ground plane the insulation will ware out.
1599930447148.png
Here is a drum coil that has flux in the air. It should not be on a ground plane.
1599930573586.png
 

Thread Starter

atferrari

Joined Jan 6, 2004
4,093

upand_at_them

Joined May 15, 2010
518
If you were building an existing design and were deciding to mount the inductor that way, then you might experience a difference in resonant frequency, if the original design didn't specify that mounting. It's my understand that this is going to matter more for higher (RF) frequencies that radio circuits encounter. If this is your own design, and you're starting from scratch, then I wouldn't worry. If frequency stability is a concern I would make sure that it's securely mounted and not allowed to bounce or even rub against the board.
 

MisterBill2

Joined Jan 23, 2018
7,021
While there is not much magnetic flux on the outside of a toroid, there is some, and so there will be some effect. BUT there will also be capacitance to whatever conductors are next to the windings and that will certainly have an effect.

One more comment is that not every piece of commercially sold electronics uses the very best design possible. In fact, over the years there has been some real junk produced and sold. So just because you see it in commercially sold equipment does not mean that it is a good idea.
 

MisterBill2

Joined Jan 23, 2018
7,021
Very interesting...
So, how in toroidal transformer almost 100% energy transfers from primary to secondary windings without 100% outer magnetic flux?
The toroidal transformer uses all of the windings around the same core, thus all of the flux is routed through the coils. So it is important to understand what others actually mean when they repeat things. It is also useful to be aware of how toroid transformers are constructed. And given the number in use that are working very well, it is handy to recall that seeing magnetic flux is difficult for most folks.

And all should be aware that the package shown in post #6 is a rather poor arrangement as far as the mounting of the inductances goes. The conductive aluminum case acts like a shorted turn at the end of the large coil, and the capacitance from the winding on the toroid certainly does not improve the efficiency of that circuit at all.
 
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