Re: Power Output


Instead of spreading a toroid inductor's winding fully around its circumference, it is better to reduce the winding portion from 360 degrees to 330 degrees.  The 30-degree gap thus created is then the form's surface that fits against the circuit board.  This reduces the capacitance between the outer surface of the windings and the ground plane effect of the circuit board.


A small piece of cork, 1/16" thick, cut from a wine bottle cork can be fixed with glue between the 30-degree gap on the form and the circuit board.  This will increase the separation between the two and also give a cushioning effect to the finished assembly.


Several years ago, a 1,500-word article I authored on how to wind and mount toroidal inductors was published in the QRP Quarterly.  If anyone would like to have this, please let me know.


Charles, W2SH

From: <> on behalf of Dave Benson <davek1swl@...>
Sent: Wednesday, March 9, 2022 7:17
To: <>
Subject: Re: [4SQRP] Power Output

(This is general information, and not aimed at you)

The higher-than-expected inductance isn't just a 4SQRP thing. It's a common source of difficulty.  There's always stray capacitance between adjacent turns.  The calculations for inductance don't include that. They can't, since it's up to the care the builder takes when winding the toroids.  (Heavier-gauge wire also increases the effect due to its larger surface area. )

 It's important to make sure the turns are evenly spaced and spread out around the entire circumference of the toroid. This minimizes that unwanted effect. 

73- Dave, K1SWL

On Tue, Mar 8, 2022 at 8:36 PM Douglas L via <> wrote:
About 2 turns need to be taken off several toroids in order to raise the frequency from around 3.6 MHz up to about 3.8 MHz where most AM activity is located.  
I’ve posted a bit about this on the Nouveau 75 user group’s site.

I wonder if toroid values are a problem in the other 4SQRP kits?


On Mar 8, 2022, at 5:32 PM, Curt via <> wrote:

Did you try spreading or squeezing the windings on the toroids? 

If you did adjust a toroid, you need to lift only one side. Kits should instruct up to tack solder one end down for these adjustments, as I confess in building several dozen rigs I still haven't learned that. 


Charles Moizeau, W2SH

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