Re: Toroid winding numbers and measurements

Paul Jorgenson KE7HR

An example of different amounts of core coverage with a given number of turns vs. inductance is at:

As a practical matter, different mixes (stuff the toroid is made of) have frequency sensitivity. Look at the data sheets or use the calculator available at

Will it make a difference to your project? You have to experiment. The range of possible values of the capacitors and inductors make it difficult for the designer to cover all the bases in a low cost, high performance, complex circuit. You have to experiment.

The case of having 20 or so turns and having to remove one or two is well within the range of the actual permeability range of the cores - 5% to 10%. I was just working on a circuit (not a QRP Labs circuit) that has three equal inductors in the filter. To get the peak response where I need it, I had to remove one turn from two of them and three from the other. In this circuit, I had modeled (Experimental Methods in RF Design software - sadly no longer available) the response to have an insertion loss of about 3 dB. I ended up with about 20 db insertion loss. I had modeled the Q of the inductors to be 200 and had to change the modeled Q to be 50 to match what had been built. Time for much larger cores with much larger wire on that one to get the Q up!

So, go out and get a cheap inductance meter (eBay $10 to $50) if you are going to participate in busting on the design and make some of your own measurements and provide data and not just a complaint.


Paul KE7HR

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