[TowerTalk] New Larger Fair-Rite #31 Toroid

Jim Thomson jim.thom at telus.net
Tue Mar 28 12:00:19 EDT 2017


Date: Sun, 26 Mar 2017 16:22:58 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: Rfi List <rfi at contesting.com>, towertalk reflector
<towertalk at contesting.com>
Subject: [TowerTalk] New Larger Fair-Rite #31 Toroid

KY8D asked me about a new, larger #31 toroid that has recently been 
added to the catalog. It's 4-in o.d., 3-in i.d, and 1-inch long.

http://www.fair-rite.com/product/round-cable-emi-suppression-cores-2631814002/

Note the impedance data for 1, 3, and 5 turns at the bottom of the page.

Gan's email arrived today (Sunday) so I haven't had the opportunity yet 
to investigate pricing. My guess is at least double the cost of the 
2.4-in toroid, but because it's twice the length (1-in as opposed to 
0.5-in for the 2.4-in toroid), a single core will likely be equivalent 
to two of the 2.4-in cores, so fewer cores will be required to achieve 
the same choking Z. More important, the much larger i.d. will allow more 
turns and/or larger coax.

73, Jim K9YC

##  I saw the  new  4 inch OD  x 3 inch ID  x 1 inch long  type 31 torroid on their
site over a year ago, I believe its been there for quite some time.  If you look at the
impedance data  for 1,3,5 turns, at various freqs, you will see that the new bigger torroid
has just a hair higher results  when you rapidly toggle  between the 2 x cores.  Unless  you are
hell bent trying to stuff more than 7 turns of  RG-393  or RG-213 through a torroid, IMO, the
bigger 4 inch OD torroid really buys you nothing..and its twice the length to boot. Its also 2.5
x  heavier.  420g  vs  117g.

##  Danny,  E73M, and myself looked at the new  4 inch OD torroid, and discarded it soon after.
The ID is simply too big, being a whopping 3 inch ID, so even though its twice the length of the
smaller  2.4 inch OD x 1.4 inch ID, it buys you nothing when you measure both of the torroids,
with 1-7 turns of  393 or 213 .    The smaller torrid is only half the length, and works 99% as good.
If you say had a requirement for  6 x 2.4 inch cores... = 3 inches long..... you would require 5 x 4.0
inch cores to do the same thing.....  =  5 inches long. 

##  The bigger 4 inch core would be ideal if trying to wind flexible power cable around it..or something
like LMR-600UF etc. 

Jim  VE7RF   






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