[RFI] 2.4" OD #31 toroids

[Jim Brown]

On 1/30/2012 5:24 AM, Pete Smith N4ZR wrote:
> Does anyone have a source for these?

See Appendix One of http://audiosystemsgroup.com/RFI-Ham.pdf for part 
numbers and reliable sources.  I've done well for moderate quantities 
with Kreiger, which is in the Roanoke area.  It pays to shop around -- 
the prices can vary depending on what they have in stock, left over from 
a big order they bought for another customer.



Yes, you want the #31 material, and the most useful sizes are the 2.4-in 
i.d. toroids and the 1-inch i.d. "biggest clamp-ons" listed in the 
Appendix.  Study the graphs of Z vs frequency and number of turns to 
guide you in winding the chokes.  Yes, a single core is enough IF you 
can get enough turns on it. RG58 would make that easier, and this would 
be a great application for one of the bifilar chokes wound with THHN. 
Make sure you're  looking at the latest version. These chokes have been 
in the tutorial for about a year and a half.

And the traditional ham vendors who advertise in QST (Amidon and their 
ilk) are USELESS for these ferrite parts  -- they are SALESMEN, not 
engineers. There used to be a guy named Amidon who WAS an engineer, but 
he's been dead a long time. My stuff has been on the internet for five 
years, and they're still not stocking #31. AND their prices for what 
they do sell are outrageous, more than double what you would pay from a 
GOOD vendor like Mouser, Allied, Newark, Krieger, Lodestone, etc.

Another idea, Pete. You might consider a group purchase for PVRC and 
other clubs near you. Between PVRC, FRC, and YCCC, you could build huge 
quantity and get a great price. NCCC has done three big group purchases. 
K6EU did a couple, I did the last one, about a year ago, and we were 
able to get the 2.4-in toroids for $4.10 with shipping (we ordered 1,000 
pieces). We bought direct from Fair-Rite, which is easy to do, but 
requires that you spend at least $500 and buy in box quantities.  We've 
also found the best price on the big clamp-ons from distributors. 
Fair-Rite will also ship to multiple locations, but always in box 
quantities. I wouldn't push this too far, but it should be no problem to 
ship to a single YCCC point, a single FRC point, and a single PVRC 
point.  For the NCCC order I did, I established a rule that distribution 
would be only at club meetings. This was for my convenience, because I 
didn't want to be in the shipping business, and also because ferrite 
parts are quite brittle, and must be very carefully packed.

73, Jim K9YC