Thank goodness it's a <plastic> NEMA box (the choke would do nothing in a metal
box).
But why use a box with bulkhead connectors anyway? That seems to be the root
cause of all the problems.
I never use bulkhead sockets on anything outdoors, because they require
stripping the coax which creates opportunities for water leakage, bad solder
joints and corrosion - all of which can be avoided by using inline connectors.
If you don't need someplace to fix bulkhead connectors, then you don't actually
need a box either.
Would there be any problem about using inline connectors and no box at all?
That would cure your space limitations :-)
From limited experience with smaller cores, cutting cores in half and
re-joining them is not a good way to go. You'll probably lose several cores in
learning the best way to do it, and ferrite makes razor-sharp flakes so you'll
almost certainly lose some blood as well. And even after all that effort, you
won't ever get back to the AL value of the original core. Just don't go there
at all.
Interesting question about binocular arrangements of cores (two short stacks of
cores side by side, vs one tall stack). I found K9YC's comparative measurements
[1] but am struggling to explain either (a) the shift in resonant frequency or
(b) the difference in |Z| magnitude.
[1] http://www.k9yc.com/CoaxChokesPPT.pdf
73 from Ian GM3SEK
>-----Original Message-----
>From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
>Jim Thomson
>Sent: 10 February 2015 10:25
>To: Ian White; towertalk@contesting.com
>Subject: Re: [TowerTalk] Cutting a FT-240 type 33...in half ??
>
>It’s a thick walled plastic nema box.... and toroids are type 31, not type
>33.
>7-17 female connectors on each end. Existing chokes consist of 4 turns of
>393
>through 4 x type 31 cores. Steve, G3TXQ tried 4 x turns of 213 through 4 x
>cores and
>found the Z was a little over 3 k ohms from 13-27 mhz. I need to use one
>box for 15m,
>and the 2nd box for 20m. Without mucking it up too much, I believe I can
>add at least
>one more core, perhaps 2 cores to the 15M box....and possibly 2-4
>additional cores
>to the 20m box.
>
>I also need to build two more boxes, one for 80m, and the 2nd for 40m.
>These are all monoband
>chokes, so they only have to work good one one band. I think the max turns
>that can be stuffed through
>these 1.4 inch ID cores is aprx 5-7 ? 393 coax is is bit smaller OD vs
>213. .391 inch vs .405 inch.
>
>Something else I cant fathom is the use of cores on both sides of the coax
>loop. IE: 3-5 x cores
>at 9 oclock position...and 3-5 at the 3 oclock position...... vs 6-10 cores
>all stacked on one side.
>K9YC sez the binocular format is not optimum. I just don’t understand why.
>I only have so much
>room in these nema boxes... so cant have huge loops on the outside of the
>cores. I also cant
>have loads of space between the loops on the outside. I can only cram so
>many torroids in there
>and only on one side. Think it was like 6-7 max. Im also trying to
>extrapolate K9YCs info, plus factor in
>tight turns, with no space between em. 6-7 x cores + 5-7 turns might do
>the trick for either, or 80
>and 40m. I need to optimize for 80 and also 40m, separate chokes, the
>best I can, with the
>constraints I have.
>
>Jim VE7RF
>
>
>-----Original Message-----
>From: Ian White
>Sent: Monday, February 09, 2015 11:42 PM
>To: 'Jim Thomson' ; towertalk@contesting.com
>Subject: RE: [TowerTalk] Cutting a FT-240 type 33...in half ??
>
>Hold on, Jim -
>
>Please say that <isn't> a metal NEMA box with flange connectors at both
>ends?
>
>
>73 from Ian GM3SEK
>
>
>>-----Original Message-----
>>From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf
>Of
>>Jim Thomson
>>Sent: 10 February 2015 05:56
>>To: towertalk@contesting.com
>>Subject: [TowerTalk] Cutting a FT-240 type 33...in half ??
>>
>>Ok, I have a requirement where an additional one or two x 2.4 inch
>OD,
>>type 33 cores needs to be added to an existing choke balun.
>>Since each end of the RG-393 silver plated + teflon coax is already
>silver
>>soldered to a 7-16 DIN connector at each end of the nema box,
>>I would rather not have to take the entire assy apart. Major pita.
>393 coax
>>has TWO silver plated braids, and in this case, each of the braids has
>been
>>carefully
>>separated at each end, and each braid is silver soldered to a lug,
>that is
>>bolted to the 7-16 din connector flange, via the SS 8-32 machine
>screws.
>>IE: 2 of the 4 corners of each 7-16 din female coax connector gets a
>braid
>>attachment.
>>
>>Can a 2.4 inch OD, 1.4 inch ID, type 33 toroid be cut in half, edges
>sanded,
>>then placed around the existing 4-5 turns of 393 coax, then
>>held together via glue, ty-raps, both, or some other method ??? I
>have an
>>excellent H-V bandsaw, made for cutting steel, hard steel, and AL.
>>IE: 80-120-200 ft per minute. It would slice through a toroid very
>quickly.
>>If what I propose is feasible, it would save me a lot of grief.
>>I already checked, and the big, type 43 snap on types will not fit,
>since they
>>only have a 1 inch ID.
>>
>>Tnx...... Jim VE7RF
>>
>>
>>
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>>
>>
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