The advantages of separate the cores is that you enhance the cooling. The cores
will not get so hot as you allow for more air flowing past. You will increase
the capacitance as you will need more wire.
Hans - N2JFS
-----Original Message-----
From: Roger (K8RI) on TT <K8RI-on-TowerTalk@tm.net>
To: towertalk <towertalk@contesting.com>
Sent: Sat, Nov 1, 2014 1:15 am
Subject: [TowerTalk] Another one off balun capacitance question.
I asked this before but with a bit different wording.
What about core spacing in a multi core balun? I have 6 and 7 core
baluns with 6 and 7 turns of coax. I'd have to look up the coax
designation, but it's roughly 1/4" OD with a Teflon dielectric and
silver plated shield braid. I'll be running the legal limit into a 160
half sloper with the balun at the feed point.
I have one set with the cores super glued together in a stack and am
building another set with 1/4" spacing between the cores. With the 1/4
inch spacing, I just mill 1/8th inch deep slots in 1/4" plexiglass the
width of the core thickness and a 1/4 inch spacing between the slots. I
use a rather thin epoxy to wet the surface of those slots and slide them
into place. Yes it's fragile and I'm looking at Lexan.
The coax is epoxied to the inside of the cores and held within an inch
of the OD using a ventilated sleeve. (thin wall plastic sewer pipe)
Overall, the coax spacing to the core will be much less than in many
choke baluns.
I use a piece of 1" X 1/8th inch Aluminum angle set in "V-blocks" to
line up the cores while waiting for the epoxy to set. I use the same
set up when sticking the cores together with super glue. Just 3 or 4
"small" drops spread out is plenty and has less risk of your fingers
becoming a permanent part of the cores..
"I think" the cores spaced 1/4" will give less C...maybe. The area of
coax to cores is the same on the inside although the cores are close
spaced in one instance and have a 1/4" spacing in the other although the
surface area is the same.
73
Roger (K8RI)
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