On 7/21/20 11:49 AM, Steve Maki wrote:
I've seen similar issues and no longer depend on the normal bolt and nut
shield connection when there is a layer of PVC involved which is
compressed by the bolt & nut. Any shrinking of the PVC will cause an
intermittent connection. Most commercial baluns are still made this way.
Or 4 nuts - nut1 wire nut2 pvc nut3 wire nut4
The preload between nut1 and nut2 and the preload between nut3 and nut4
are what make the contact. Takes two wrenches to get it tight enough.
Instead I replace one of the 4 machine screws with a solid #14 or #12
wire that is soldered to the SO239 and sticks into the box 3/4" or 1",
which the coax shield can then be soldered to.
That works fine for a coax connector, although now you've got a
"non-disconnectable" connection.
Actually, a banana jack/plug would probably work. They're spring loaded,
so they don't have thermal cycling issues.
-Steve K8LX
On 07/21/20 14:23 PM, dj7ww@t-online.de wrote:
Before WX0B switched to use feed through insulators I replaced two of his
baluns on Optibeams at a friend.
Baluns were made from RG393 wound through ferrite toroids.
Around the stainless steel screws the boxes were burnt out, I guess
that was
caused by current, not by voltage and went into a loose connection and
thermal runaway.
I also use feed through insulators, either ceramic from my junkbox or
home
brew teflon.
New insulators can be found here:
https://www.daburn.com/10-58ceramicfeed-thruinsulators.aspx
73
Peter
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