On 11/2/19 10:18 AM, Jim Thomson wrote:
Date: Sat, 2 Nov 2019 13:25:19 +0000 (UTC)
From: Roger Parsons <ve3zi@yahoo.com>
To: "Tower and HF Antenna Construction Topics."
<towertalk@contesting.com>, "jim@audiosystemsgroup.com"
<jim@audiosystemsgroup.com>
Subject: [TowerTalk] Ferrites 31 vs. 77 material
<Very funny.
<The posts from both N6RK and AB7E support my statement that variability in
ferrite parameters has been known for a very long time. You're the one who
asserted that it has just been discovered and that therefore Steve G3TXQ could not
have known about it.
<73 RogerVE3ZI
## I believe it was N3RR that bought 700, (seven hundred) type 31 cores
from one supplier, all from the same lot number..2 years ago. He used a
simple 1 turn link to test them..and then graded them. They were all over the
map, + and – 22%. Thats a whopping 44% spread. No 2 ferrites the
same! ALL made in China......so what do you expect ? So much for fairite
moving their factory to China. QC down the tubes ever since.
+/- 20% is a reasonable tolerance for this kind of component -
from Dexter Epcos:
"Even with the best grinding methods known today, a certain degree of
roughness on ground surfaces cannot be avoided, so that the usual term
“without air gap” or “ungapped” does not imply no air gap at all. The AL
values quoted allow for a certain amount of roughness of the ground
faces. The tolerance of the AL value for ungapped cores is –20 to +30%
or –30 to +40%. Closer tolerances are not available for several reasons.
The spread in the AL values of ungapped cores practically equal the
spread in ring core permeability (±20% … ±30%), and the AL value largely
depends on the grinding quality of the matching surfaces."
https://www.ferroxcube.com/en-global/download/download/11
the "filter" materials (material 3C11, page 77) show mu has a +/- 20%
tolerance (yeah, it's for a lower frequency, but I didn't want to go
hunting for one for HF...)
There's also a strong temperature dependence on some of these
materials.. mu might go from 1500 at 0C to 2000 at 50C.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|