## March 25, 2010

I was messing around in the shack today, breadboarding a signal generator circuit from Ashhar Farhan's (VU2ESE) Web site. He wound his coils on fast-food soda straws, I didn't have any straws lying around, but I did have a bunch of T50-2 powdered-iron toroids, so I decided to use a couple of them. I wasn't entirely sure about the inductance of VU2ESE's coils (he just gave the number of turns), but he did mention that he designed the signal generator circuit to run from 3 to 30 MHz, and given the size of the tuning capacitor, I did some rough calculations concerning what inductance would be required to resonate in that range.

Armed with that information, I went Googling in search of a toroid calculator, and found this calculator site, with exactly the sort of toroid calculator I needed. You just pick the type core you're using (iron powder or ferrite), pick the core size, enter the desired inductance, and the calculator gives you the number of turns to wind on it.

I thought it was pretty cool, anyway, and it saved me some time (and math).

73 de aa0ms

Alan Yates said...

I find the site http://toroids.info/ quite good for toroid calculations, at least as a starting estimate. Once wound, I measure the inductance with a Carver-style LC tester to double check, the core material has a pretty large tolerance and the winding layout makes an even larger difference.

I wrote an LC calculator to do the band set/spread calcs:

http://www.vk2zay.net/calculators/?body=vfoHelper.php

Unfortunately it is quite old and I haven't ported it to the more friendly input handling code. You have to use exponent notation to input the values rather than being able to use SI prefixes (i.e. 3.3e-6 instead of 3u3).

Doug, AAØMS said...

@Alan Yates:

I took a look at the http://toroids.info site--it's a very handy site--thanks for the suggestion. I also very much like your calculator page--lots of interesting and useful stuff there. Thanks!