Larry,
Could you expand a bit on that...
I don't see where mix61 is a better choice over mix31 at HF, other than
the curie point is substantially higher for 61, which allows you to heat
it up more.
Yes with a 31 choke one would need higher impedance to keep heat down
below the curie point, but so what, I want higher impedance in my
chokes... Why does that make 61 a better choice than 31?
Mix61 looks worse to me than 31 for HF, pretty much across the board...
Help me understand you point here please...
73s and thanks,
Dave (NK7Z)
https://www.nk7z.net
Award Manger, 30MDG Grid Awards
ARRL Technical Specialist
ARRL Volunteer Examiner
ARRL OOC for Oregon
On 2/3/19 7:06 AM, Larry Benko wrote:
Jim,
I respectfully disagree with your comment about 61 material cores not
being useful at HF. For transmitting applications they are quite
valuable. The low Q impedance provided by 31 materials is the go to
solution for receiving applications but at high power care must be taken
to ensure that the impedance is much higher than needed to keep the 31
material from overheating. This is made even more difficult since the
common mode impedance in a circuit is unrelated to the differential mode
impedance and calculating what common mode current might flow through
the common mode choke is not easy to do. Of course you can sneak up on
the problem by just making the choke and slowly increasing the power at
all frequencies you use and see if it gets too hot in your application.
Not very scientific but common mode circuits are elusive to understand
and simulate.
Larry, W0QE
On 2/2/2019 3:30 PM, Jim Brown wrote:
I also recommend Arrow, both for cost and service, especially for
small quantity. It helps a lot that shipping is free for an order of
$20 or more -- IF it's a web order for what's in stock. I also got a
very good price on 100 pieces of the 2.4-in o.d. #31 toroids. Other
good vendors are Lodestone Pacific, Dexter Magnetics, and the usual
industrial electronics houses like Newark, Allied, Mouser, etc.
Note also that there is currently a tariff on these parts, which are
made in Fair-Rite's factory in China.
BUT -- #61 cores are NOT of much use for RFI suppression below UHF,
and they are a terrible choice for a common mode choke (often called a
"current balun").
73, Jim K9YC
On 2/2/2019 9:04 AM, Tom WA9WSJ via RFI wrote:
Hi John,
I once bought some big cores from these guys,
https://www.jpmsupply.com
(FT140-61 ferrites). At that time, a little over a year ago, they
were the best prices I could find.
They do have a couple other types. Maybe they can help you.
Good luck!
73 Tom
On Saturday, February 2, 2019, 9:26:14 AM MST, John Altman
<wa4aip@gmail.com> wrote:
Which company is the best source for bulk bead orders?
Tks,
John
WA4AIP
ARRL Charter Life Member
Sent from my iPad PRO
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