2019-03-07 Make a 4 Millihenry RF Choke

From FB group Building Transistor Radios Mar 7

I got some of these toroid cores a few months ago, and I got around to experimenting with them. I wound one with 21 inches (51 cm) of 30 AWG (.25 mm diameter) enameled wire. This covered the core with a single layer of wire. I measured the inductance at 4.1 millihenrys. I’ve often seen regenerative or reflex radios that need an RF choke about this value, so this looks like a very inexpensive way to make an RFC. I got these from Electronic Goldmine, they have a $10.00 minimum.

https://www.goldmine-elec-products.com/prodinfo.asp?number=G23258

Update Mar 9 – According to this website, the Al value is the inductance divided by the turns squared. Using 4 millihenrys and 44 turns, this calculator gives me Al = 2066.

http://www.encyclopedia-magnetica.com/doku.php/calculator/al_value_from_inductance_and_number_of_turns

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