[TowerTalk] 40M rotary dipole and CM current

[Grant Saviers]

Yes, D-104 lip zaps were so much joy.  3rd floor attic shack, Viking 
Valiant 200w AM transmitter, random length end fed long wire. Ground?  
We got no stinking ground!  A death grip was needed on the D-104 PTT 
lever.  Long before ANY digital stuff in the house, otherwise all of it 
would have been lit up.  However, the blue arc haze around the Heathkit 
air core balun was a fun to observe when the SWR really got nasty.

Grant KZ1W



On 9/23/2017 11:03 AM, Patrick Greenlee wrote:
> 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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