[UK-CONTEST] OT Where to buy FT240-31 or similar cores in the UK?

[Ian White GM3SEK]

Peter Howson wrote:

>>From: uk-contest-bounces at contesting.com
>>[mailto:uk-contest-bounces at contesting.com] On Behalf Of Ian Burns
>>Sent: 25 February 2010 20:24
>>To: UK Contesting
>>Subject: [UK-CONTEST] OT Where to buy FT240-31 or similar cores in the UK?
>>
>>
>>Please excuse the bandwidth, this is off topic but someone here will 
>>probably know.
>>
>>Where can I buy FT240-31 or similar toroidal cores in the UK?
>>

>
>Sycom -- http://www.sycomcomp.co.uk/ -- have type 43 and 61 listed in 
>240 size.
>
>Also Modecomponents -- http://www.modecomponents.co.uk/ -- stock a good 
>range but not this particular one. But Chris G8CHW may be able to get 
>them for you.

Be sure to buy the right grade of ferrite for what you want because 
FERRITES ARE NOT INTERCHANGEABLE (yes, I am shouting :-)

Fair-Rite grade 61 (six one) is good for choke baluns at 20-15-10m, but 
the more recent 31 (three one) is *far* better for choke baluns at low 
frequencies, and also for EMC chokes in non-transmitting applications at 
any frequency.  The older and better-known grade 43 is a general purpose 
HF grade, but better chokes can be made with 61 or 31 in their 
respective frequency ranges.

Dust iron cores (eg T200-6, without the F at the beginning) are 
categorically NOT suitable for choke baluns or EMC chokes.

If you're buying toroids for winding any kind of cable chokes, 2.4in is 
the only practical size, ie FT240-xx. Smaller toroids don't have enough 
room to wind multiple turns. Small-hole beads are very poor value 
compared with toroids, which means that people often don't use enough 
beads and then wonder why their chokes don't work (or only work in 
situations that are 'soft targets').

Among the UK amateur dealers, Sycom stock the FT240-43 and -61; JAB list 
only the FT240-61 but it isn't available; and Mode Components do not 
list any of these large toroids. Despite heavy hints, no UK amateur 
dealer stocks the FT240-31... but maybe this isn't surprising, because 
they have to buy from the USA on exactly the same terms as an individual 
importer.

As far as I know, the only sources for the FT240-31 are in the USA but 
you need to order in some quantity:

* Mouser (www.mouser.com) have a free Fedex shipping deal on orders over 
£50

* Farnell (uk.farnell.com) charge £15.95 per order on items from their 
US company Newark.

Both companies stock FT240-31 (but not the FT240-61 or -43). In both 
cases you will have to pay VAT but they handle the importation process. 
Farnell are very quick - you're billed in the UK and they ship by UPS 
the same day (US time) with no further delivery/collection charges. I 
haven't personally used Mouser so the details may be different.

I will not use Amidon ever again. Prices are far higher than Newark or 
Mouser, and a whole sheet of "FT240-31" bought in the USA at great 
expense and hand carried back, turned out to be grade 43. Essentially 
Amidon take the obscure Fair-Rite stock numbers, change them to a more 
readable "FTxxx-yy" format... and then double the price.

Newark and Mouser use the original Fair-Rite stock numbers; if anyone 
wants them, please e-mail.

Having said all that, I've recently been working on a range of ferrite 
chokes that avoid having to buy big toroids at all. They are based on 
some Fair-Rite 43 beads which are a standard Farnell UK stock item (so 
there's no US order surcharge). Performance isn't quite as good as the 
very best chokes using multiple FT240 toroids, but better than any 
straight string of 20-30 beads. Above all they are far more 
cost-effective given the prices we have to pay for 'named ferrite' in 
the UK.

Details will be in May Radcom. I'm also looking for some beta testers so 
if anyone is genuinely intending to make some chokes in the very near 
future (as opposed to generally curious), please e-mail.



-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek