Re: MFJ Drift Mods


From: Mike Czuhajewski (
Date: Mon Jan 16 1995 - 06:26:40 EST

Argh....this is not "get down on Joe" month, but he made an error in
his commentary on VFO stability: In paragraph 5 of his commentary,
N2CX said that light tan Amidon/Micrometals cores are type 7, with
tempco of 30 PPM. Close, but no cigar. Actually, type 7 with 30 PPM
is colored white when it comes from Amidon/Micrometals. You would
probably want to avoid the light tan cores like the plague. They do
have an excellent tempco--in fact, it's 0 (zero) PPM! Unfortunately,
though, the permeability is a bit low for our VFO uses--it's 1 (one),
and you just might remember that air also has a permeability of 1, too.
The material is type 0 (zero), and although it is often listed in the
same chart or list as their powdered iron cores, it is actually made of
phenolic and has no magnetic properties. It's more of a convenient
coil form than anything else, and does not raise the inductance of a
core above the value it would have if air-wound. I think the fact that
it's phenolic may be mentioned in some of the later versions of the
Amidon toroid booklet that they sell (not the free brochure they give
away), and in any case it can be verified by looking at Catalog 3, RF
Applications, from Micrometals. In Issue D, which may still be the
latest version, it's in a chart on page 2, titled General Material
Properties for RF Cores, and is at the bottom, right below type 42. I
once called up Micrometals and verified that it was phenolic, and he
said it has about the same magnetic properties as a block of wood :-)
The bottom line is that type 6 (yellow) material is good for VFOs, with
a low tempco, type 7 (white) is a bit better, but don't use the tan
cores unless you have a lot of wire to wind a LOT of turns! 73 and
Queue Our Pea DE WA8MCQ

Mike Czuhajewski, user of the UniBoard System @
The WB3FFV Amateur Radio BBS - Located in Baltimore, Maryland USA
Supporting the Amateur Radio Hobby, and TCP/IP InterNetworking

Search QRP-L Archives

[ QRP-L Archive | ]
[ 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 ]


This archive was generated by hypermail 2b29 on Fri Jun 02 2000 - 11:27:37 EDT