[Elecraft] BL2 choking Impedence measurements?

[Jim Brown]

On Thu, 26 Aug 2010 12:51:06 +0100, CUTTER DAVID wrote:

>What is going through my mind is how the amateur fraternity could persuade
>a distributor in EU to stock these and the type 31 cores.

I suspect that all it takes is a large order to get their attention. Many 
of the folks who work in these facilities are living the deep past, and 
stock what they used to sell. The #31 material is a relatively new 
material, developed around the turn of the century (2000) and first showed 
up in the 14th Edition of the Fair-Rite catalog. Not all sizes of cores 
were listed. When I was doing my initial work on the use of ferrite cores 
for RFI suppression in audio applications, I ordered a lot of samples from 
that catalog. Early on in my work, I called and requested #31 cores in the 
2.4-inch o.d. size, and was told they were not available. A month later the 
rep called me back and said he had five samples for me!  

If you look at the current catalog (15th edition), you will see that #31 is 
now listed as their standard mix for suppression at HF, for the most part, 
replacing other materials. 

Here in the US, over a period of about five years, we've organized a dozen 
or so large group purchases of a few selected sizes of cores to get a good 
quantity price from distributors. The first order we did was for more than 
1,000 pieces, and was combined from clubs in Chicago, Minneapolis, 
Indianapolis, and Los Angeles. We paid about $4 each for the 2.4-inch 
toroids in #31 material. The next order I was a part of was nearly three 
times that size, and the price we negotiated held for one year, during 
which time we were able to add to the order. As a result, main line 
industrial electronics distributors like Newark, Allied, and DigiKey are 
now stocking some of these parts and offer decent prices, even for much 
smaller quantities. Fair-Rite was happy to deal with us directly if we 
wanted, and we did for part of a couple of orders. But in some cases, we 
got better prices from distributors. 

There is a list of suggested distributors in Appendix One of my tutorial, 
along with a list of suggested parts to buy, and a worksheet to help 
estimate how many you should buy. The worksheet assumes you are buying in 
quantity and buying for use over a period of 3-5 years for general RFI 
suppression and making transmitting chokes, and is based on your own 
personal hamming activity. 

http://audiosystemsgroup.com/RFI-Ham.pdf 

It's a sure thing that if you walk up to a distributor with an order for 
500 ferrite cores you'll get them, and at a good price. The parts that I 
recommend that you order are the 2.4-inch o.d. toroids, the "biggest clamp-
on," and the clamp-on that fits on RG8. You won't use it for RG8, but it is 
quite useful for wrapping multiple turns of small wires attached to noise 
generators like power supplies, computers, and the like, and around audio 
cables that are picking up RFI in your stereo (or a neighbor's). By 
limiting yourself to those three parts, you have the most useful, and you 
build quantity. 

73, Jim Brown K9YC