[TowerTalk] VSWR Heating in Chokes and Baluns

[David Gilbert]

I've done a BUNCH of Google searching using (among others) the search 
phrases "dielectric properties of ferrites", "heating effects in 
ferrites", "VSWR failures of baluns", etc and so far not found a clear 
discussion of the topic.  That first search phrase alone generated 
1,230,000 hits and while I obviously didn't check them all I did check a 
LOT of them.

I remember, though, previous discussions here on TowerTalk where more 
knowledgeable people than either you or I pointed out that damaging core 
heating in a typical ferrite balun or common mode choke is far more 
likely to be the result of dielectric losses due to high VSWR than it is 
due to eddy current losses due to high current in the winding.  I just 
hoped that one of those people would know of a technical link that more 
rigorously describes the condition.

What I do know is that ferrites are basically an iron-based ceramic with 
other materials (usually other metals) included as dopants to get 
various desired properties, such as mu or best frequency range. Being a 
ceramic, ferrites are basically insulators with both a dielectric 
constant and a loss tangent that results in current flow (and therefore 
loss and heating) under RF voltage (E-field) excitation.  That E-field 
could logically be the result of a high VSWR ... just like the folks who 
have stated same in the past.

As I remember, you were asking for others to do some studies that you 
could have done yourself.  I'm merely asking for a link if anybody knows 
of one.

Dave   AB7E



On 9/3/2020 11:54 AM, Ron WV4P wrote:
> *Dave,
> *
> *Is that not something you should do yourself ? I recall the advice 
> you gave me...
> *
> *
> *
> /"Neither is expecting/
> /someone else to do all the work give you all the answers.
>
> Dave AB7E"/
>
> *Perhaps this is some testing you should do on your own, or at least 
> the Google search to find other people's work ? *
> *
> *
> *Thanks again for  your help when I had questions on Baluns.. *
> *
> *
> *Ron, WV4P*
>
> On Thu, Sep 3, 2020, 1:14 PM David Gilbert <ab7echo at gmail.com 
> <mailto:ab7echo at gmail.com>> wrote:
>
>
>     Can anyone point me to a technical reference that discusses
>     dielectric
>     heating (not magnetic flux related) due to high VSWR in the
>     ferrite core
>     of a balun or common mode choke?
>
>     Thanks much,
>     Dave   Ab7E
>
>
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