EMRFD Message Archive 5160

Message Date From Subject
5160 2010-09-17 07:32:03 Tim Toroid transformer flux/watt limits?
Many many years ago (possibly in SSDRA, possibly on the thin-paper Amidon flyers) I remember a chart with an accompanying formula, that was intended to give some guidance as to how many watts could be run through various RF ferrite transformer cores.

IIRC one of the important quantities included max flux for a given frequency (I think read off a graph for each mix).

Can someone help me link my vague memories, to a specific reality? e.g. say I want a 1:4 balun for 10 Watts on 30 Meters. What size core do I need for a 43 mix ferrite transformer? If one side of the transformer is carrying DC (as opposed to just AC) current does this make it more complicated?

Now that I think of it I'm pretty sure it was that thin-paper Amidon tech data flyer that I'm thinking of. Is that available online? Amidon website lets me order a free paper copy but the paper copies rarely last more than a few weeks on the bench here :-(. An online reference that didn't suffer from coffee spills would be best!

I notice a lot of the commercially available baluns seem to use iron powder toroids (e.g. -2 mix) in the transformer. I thought ferrite materials would give a higher coupling K, so I'm guessing there's some design feature that compensates here.

Tim N3QE
5162 2010-09-17 08:06:19 w4zcb Re: Toroid transformer flux/watt limits?
Many many years ago (possibly in SSDRA, possibly on the thin-paper
Amidon flyers) I remember a chart with an accompanying formula, that
was intended to give some guidance as to how many watts could be run
through various RF ferrite transformer cores.

IIRC one of the important quantities included max flux for a given
frequency (I think read off a graph for each mix).

Can someone help me link my vague memories, to a specific reality?
e.g. say I want a 1:4 balun for 10 Watts on 30 Meters. What size core
do I need for a 43 mix ferrite transformer? If one side of the
transformer is carrying DC (as opposed to just AC) current does this
make it more complicated?
\
Amidon put out a 22 x 22 inch foldout with the info you're looking
for in a paper dated December 2001.If you can't find it online
somewhere, I have 2 copies (Keep one in the shack and one in the
shop) and I could mail you one of mine for a snail mail address. You
ought to take better care of your valued homebrew references!

Regards
W4ZCB
5164 2010-09-17 09:09:34 ehydra Re: Toroid transformer flux/watt limits?
1. I think it is the better IMD performance of powdered iron because the
saturation point is weaker.

2. With ferrites it can be impossible to get low enough practical
inductance on a toroid (to few turns).


- Henry


--
ehydra.dyndns.info


Tim schrieb:
> I notice a lot of the commercially available baluns seem to use iron
> powder toroids (e.g. -2 mix) in the transformer. I thought ferrite
> materials would give a higher coupling K, so I'm guessing there's
> some design feature that compensates here.
>