[Towertalk] Common-mode choke at 430 Mhz

[Jiri Sanda]

Hi !

On Wed, 17 Jul 2002, Larry Bush wrote:

> Building a couple of 8 element 430 MHz Yagi on 1 inch PVC boom.
>
> The driven element is a dipole with direct feed of 50 ohms. From the driven element I have 3 foot of RG-58A terminated into a type N female connector.
>
>
>
> I thought a common-mode balun wound with the RG-58 around the 1 inch OD PVC boom would be neat so I computed the reactance needed  at .4 micro-Henry, which is five turns on the boom. During my research I was could not find the use of common-mode baluns on frequencies higher than 6 meters. I have three questions:
>
>
>
> 1 Will a common-mode choke work on 430 MHz?
>
NO !
>
> 2   Will the capacity coupling between turns of the balun at 430 MHz make the choke ineffective and if so would winding the balun by spacing the turns the diameters of the RG-58 help?
>
YES !
>
> 3   How would one check the common-mode currents on the yagi models?
>
Check the SM5BSZand G3SEK sites, there is answer to all questions.
>
>
>
> Larry Bush, W5NCD
>
>
>
P.S. Yes I know about ferrite beads - it. FAR the BEST solution.

73 !

Jiri
OK1RI
P.S.1 I know also something about VHF antennas - check www.qsl.net/ok1kim
not yet upgraded but now 27 booms together long 187m.

P.S.2 Why for the God's sake you use PVC boom ? Use normall Aluminium
boom, the elements insulated above the boom and you are fine, than you can
only tape the coax to the boom and you are set !  - see G3SEK site
with measurements from the real word.
>
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