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Re: [TowerTalk] 40M rotary dipole and CM current

To: towertalk@contesting.com
Subject: Re: [TowerTalk] 40M rotary dipole and CM current
From: Patrick Greenlee <patrick_g@windstream.net>
Date: Sat, 23 Sep 2017 13:03:26 -0500
List-post: <mailto:towertalk@contesting.com>
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@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@contesting.com
Subject:        Re: [TowerTalk] 40M rotary dipole and CM current
From:   "Joe Subich, W4TV" <lists@subich.com>
Date:   Thu, 21 Sep 2017 21:07:45 -0400
List-post:      <mailto:towertalk@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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