EMRFD Message Archive 14583

Message Date From Subject
14583 2018-03-15 15:24:38 iq_rx Pot Core applications

Hi All,

Pot cores are a great way to get lots of inductance with a reasonable amount of wire.  They are much easier to wind than toroids.  As the experiments reported here indicate, they may not be the best choice when a specific value of inductance is needed, as in filters and other frequency selective networks.  I've enjoyed reading descriptions of the various experiments--thanks!

I use pot cores for low frequency broadband transformers, particularly transmission line types with bifilar and trifiler windings.  In broadband transformers, the amount of inductance needed is "enough."  There are many ways to estimate how much inductance is enough for a broadband transformer, but they all end up with some number specified as "more than about x."

As with everything else on this web site, experiments are expected, and in your application a pot core may be a good choice.

Enjoy the experiments,


14586 2018-03-15 19:23:54 jwolczanski Re: Pot Core applications
Hi Rick

These pot cores are fussy!

Somebody mentioned the mating surfaces.  I can tell you they need to be spotless.  I was having problems with making an 88mH core - the Inductances were all over the map until I swabbed the two halves with Acetone.  No tape debris allowed.  No handling mating surfaces.  No skin oil.  Never thought I'd need rubber gloves to wind coils.

I'm making that 1kHz filter from the R1 and need three 100mH inductors.  First inductor came in at 172 turns.  I wound 185 turns on inductor #2 and it was 94mH!  I reversed the two halves (another trick I learned) and it came in at 99.6mH!

So, I guess there's some variability from core to core.

I can connect one of these to my AADE Inductance meter...hold it in my warm hand, and watch the Inductance creep up...and keep going up for a bit after I removed it from my hand.

But yes, they are easy to wind.  I'll do the third one in the morning.  It's time for a cold 807 after winding those first two......

I'm using an 88mH "diplexer" from SSDRA (with .1uFd in series with 50 0hm resistor) and it provides a rather stunning amount of peaked low-pass selectivity.  I hardly notice the 4kHz butterworth filter which I made a few days ago.  It's gonna be interesting to listen to this radio (it's gonna be a DC transceiver) with the 1kHz filter in place.


Warrenton, VA