[TowerTalk] Balun for Force 12 6 Element 20 Meter

[Gary]

Jim & Steve,

	I'm not sure I follow... I have made some baluns recently with the 4 nut scheme that Jim is describing. Are you saying it is problematic or not?

Thanks and 73,
Gary kk0sd

-----Original Message-----
From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of jimlux
Sent: Tuesday, July 21, 2020 2:50 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Balun for Force 12 6 Element 20 Meter

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 at 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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