Topband: Buffaloed by a bias tee

[Pete Smith N4ZR]

Hi.  Well, it does indeed seem to clinch it - when I power the tee but 
don't draw any current, the impedance measured by the MFJ does not 
change.  So now to find some of the right sort of RFC.

73, Pete N4ZR
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On 1/22/2014 6:52 PM, Richard (Rick) Karlquist wrote:
>
>
> On 1/22/2014 12:32 PM, Pete Smith N4ZR wrote:
> . However,
>> as soon as I connect a 12V regulated supply to the bias tee - one of the
>> little radio shack variable wallwarts - the measured R drops to 5 ohms
>> and the X goes up to 19.
>
> Possibly the current through the choke is saturating it.
> If you connect the power supply but disconnect the load drawing
> current, does the impedance go back to normal?  That would
> clinch it.
>
> For the choke, be sure that you are NOT using a toroidal choke.
> It needs to be a solenoidal type wound on a ferrite rod.
> Also, do NOT use "shielded" inductors.  Ferrite beads will
> also saturate.  Most chokes you come across are the wrong
> kind.  I just bought some chokes today.  They only had two
> bins of suitable ones, out of several thousand bins of inductors.
>
> 45 uH is a little marginal, but doesn't explain your problem.
> 100 uH would be better.
>
> Rick N6RK
>