[TowerTalk] 40M rotary dipole and CM current

[Patrick Greenlee]

Decades ago I had an Atlas 350XL aboard my sailboat.  I used the 
insulated backstay for a random length vertical with a Drake tuner. My 
operating position was the nav station which put my metal hand mike 
about 9 ft from the bottom of the insulated backstay. Of course the 
antenna started at the output of the coax fed tuner less than 4 ft from 
the mike.  The 350XL was a 200 watt rig.  If I turned it up much past 
100 or so watts out on some bands/freqs I would get RF sparks jumping 
from the metal mike to my lips.

In defense of the setup... On some bands/freqs I could go full power 
without getting zapped. I had a decent ground, the engine, shaft, prop, 
and  a ton of steel in the water (fin keel.)

Patrick        NJ5G

On 9/22/2017 8:06 AM, john at kk9a.com wrote:
> I remember the biting mic/radio days. I had that happen on an expedition to
> Antigua in the early 80's using a very low beam with no balun. It is
> obviously a good practice to put a choke at the antenna. I have one on every
> antenna. Is there benefit to also putting a choke near the station entrance?
>
>
> John KK9A
>
> To:	towertalk at contesting.com
> Subject:	Re: [TowerTalk] 40M rotary dipole and CM current
> From:	"Joe Subich, W4TV" <lists at subich.com>
> Date:	Thu, 21 Sep 2017 21:07:45 -0400
> List-post:	<mailto:towertalk at contesting.com>
>
> By suppressing common mode current in TX you prevent the "random radial"
> phenomenon.  In doing so, you mitigate the "pin 1" problem by reducing
> the RF voltage on equipment cases/connecting cables and avoid issues
> of a "biting mic" (if you're old enough to remember RF burns to the lips
> from the case of a D-104).
>
> 73,
>
>     ... Joe, W4TV
>
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