RF chokes ...

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RF chokes ...

Ken G Kopp
My 80M CF Zepp has a feedline with a 2.5 mH RF choke from each side to the
station ground via a 2" wide flashing copper strap.

Never a problem with precipitation build up.

FWIW

73

Ken Kopp - K0PP
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Re: RF chokes ...

k6dgw
I believe Elecraft radios have an internal bleed but I still put a 470K
1/4 resistor in a PL-259 and use a coax tee on the back of the radio,
antenna on one arm, resistor on the other.  I've been wary of chokes,
fearing creating a parasitic machine, but I've never seen that happen. 
Precip static may not always be audible or visible on a panadapter, but
the input impedance of FET's is nearly infinite and with no place to go,
those infinitesimal charges just keep adding up the voltage on the input
capacitance.

Yes, I know "nearly infinite" is mathematically meaningless, but you get
the idea.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 9/27/2019 12:30 PM, Ken G Kopp wrote:

> My 80M CF Zepp has a feedline with a 2.5 mH RF choke from each side to the
> station ground via a 2" wide flashing copper strap.
>
> Never a problem with precipitation build up.
>
> FWIW
>
> 73
>
> Ken Kopp - K0PP
> ______________________________________________________________
>

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Re: RF chokes ...

Victor Rosenthal 4X6GP
In reply to this post by Ken G Kopp
This may or may not be a good idea. The impedance of RF chokes at multiple frequencies varies greatly, as anyone who has built a high power tube amplifier that covers 160-10 meters learns, sometimes the hard way. An open wire line used on several bands may present very high voltages at some points, which are different for different bands. So although Ken may have been lucky, your choke might go up in smoke, especially with high power.
I calculated that the voltage at the end of my open wire feedline when I transmit is as high as 7kV on 40 meters, and I’ve seen the arcs to prove it! The usual 2.5 mh choke would probably explode with the first dit. I am using a pair of 20 megohm 10kV resistors that I got from Mouser as static drains, across homemade adjustable spark gaps.

Victor 4X6GP

> On 27 Sep 2019, at 22:30, Ken G Kopp <[hidden email]> wrote:
>
> My 80M CF Zepp has a feedline with a 2.5 mH RF choke from each side to the
> station ground via a 2" wide flashing copper strap.
>
> Never a problem with precipitation build up.
>
> FWIW
>
> 73
>
> Ken Kopp - K0PP
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